CrowdSec decision list fetched, kept, and its clients banned until the decision ends (closes #106)

SWWAF_CROWDSEC_LAPI_URL and SWWAF_CROWDSEC_LAPI_KEY name an engine whose
decision list, <url>/v1/decisions, is fetched every minute with the key in
X-Api-Key and kept as a blocklist is: used while a fetch fails, and across
restarts through reputation.json. Ban decisions on an Ip or a Range end at
the fetch time plus their duration. A listed client's request is refused and
bans its netblock with the cause crowdsec until the decision ends; bans.json,
ban notes and metrics take the cause.

Judgement call: fetched every minute, not a setting.
Judgement call: a crowdsec ban never lengthens a limit ban.
Judgement call: a lifted crowdsec ban is remade while its decision lasts.

Model: opus-5-5

internal/alerts/alerts.go

@@ -46,8 +46,9 @@ const (
 	EventAnomaly = "anomaly"
 	// EventWAFBlock comes with the Core Rule Set; nothing raises it yet.
 	EventWAFBlock = "waf_block"
-	// EventReputationHit is a request whose client a blocklist or a DNSBL
-	// zone lists, or whose AbuseIPDB score is a hit.
+	// EventReputationHit is a request whose client a blocklist, the
+	// CrowdSec decision list or a DNSBL zone lists, or whose AbuseIPDB score
+	// is a hit.
 	EventReputationHit = "reputation_hit"
 	// EventSourceFailure is GeoJS failing or refusing smallwebwaf, a fetch
 	// of a list failing, a query to a DNSBL zone or a check with AbuseIPDB

internal/bans/bans.go

@@ -1,8 +1,9 @@
 // Package bans is the ban ledger: the bans smallwebwaf makes on the
-// netblocks of clients that break a rate limit or a byte limit or show a
-// clear sign of attack, and those an admin makes, with their notes, as
-// the "Bans" section of SPEC.md describes. The bans are kept in memory,
-// and written to bans.json and read from it by the state package.
+// netblocks of clients that break a rate limit or a byte limit, show a
+// clear sign of attack or are listed by the CrowdSec decision list, and
+// those an admin makes, with their notes, as the "Bans" section of SPEC.md
+// describes. The bans are kept in memory, and written to bans.json and
+// read from it by the state package.
 package bans
 
 import (
@@ -26,6 +27,9 @@ const (
 	// CauseAdmin is a ban an admin made, or one smallwebwaf made that an
 	// admin keeps. It is never dropped.
 	CauseAdmin = "admin"
+	// CauseCrowdSec is a ban smallwebwaf made for a client the CrowdSec
+	// decision list lists. It ends when CrowdSec's decision does.
+	CauseCrowdSec = "crowdsec"
 )
 
 // repeatFactor is how many times as long as the netblock's last ban a ban
@@ -40,9 +44,9 @@ type Rules struct {
 	// LimitBanDuration is how long a first ban for a broken limit lasts.
 	LimitBanDuration time.Duration
 	// LimitBanRepeatWindow is how soon after the end of the netblock's
-	// ban that ended last, other than one for a clear sign of attack, a
-	// broken limit counts as a repeat, which bans for repeatFactor times as
-	// long as that ban.
+	// ban that ended last, other than one for a clear sign of attack or for
+	// CrowdSec's decision, a broken limit counts as a repeat, which bans for
+	// repeatFactor times as long as that ban.
 	LimitBanRepeatWindow time.Duration
 	// MaxBanDuration is the longest ban for a broken limit; one that would
 	// be longer is permanent instead.
@@ -63,10 +67,11 @@ type Ban struct {
 	Start    time.Time
 	// Expires is when the ban ends, zero for a permanent ban.
 	Expires time.Time
-	// Cause is CauseLimit, CauseAttack or CauseAdmin.
+	// Cause is CauseLimit, CauseAttack, CauseAdmin or CauseCrowdSec.
 	Cause string
-	// Reason is a short text: for a ban smallwebwaf made, the limit broken
-	// or the rule that matched; for an admin's, what the admin wrote.
+	// Reason is a short text: for a ban smallwebwaf made, the limit broken,
+	// the rule that matched or the scenario of CrowdSec's decision; for an
+	// admin's, what the admin wrote.
 	Reason string
 	// Lifted is when an admin lifted the ban, zero while no admin has. A
 	// lifted ban refuses nothing, and does not make the netblock's next
@@ -123,7 +128,8 @@ type Notes struct {
 	// log's reputation names them. It is left out when none did.
 	Reputation []ReputationHit `json:"reputation,omitempty"`
 	// Request is the request that broke the limit, or whose bytes broke
-	// it, or that was the clear sign of attack.
+	// it, that was the clear sign of attack, or that came from a client the
+	// CrowdSec decision list lists.
 	Request Request `json:"request"`
 	// Requests is how many requests the netblock has sent since it was
 	// first seen, and Refused how many of them the ban has refused so
@@ -136,9 +142,10 @@ type Notes struct {
 }
 
 // ReputationHit is a reputation source that listed a client, as a
-// reputation_hit alert's detail gives it: Source is the blocklist's URL,
-// the DNSBL zone with its key masked, or "abuseipdb", and Score, for
-// AbuseIPDB alone, its score of the client.
+// reputation_hit alert's detail gives it: Source is the URL of the
+// blocklist or of the CrowdSec decision list, the DNSBL zone with its key
+// masked, or "abuseipdb", and Score, for AbuseIPDB alone, its score of the
+// client.
 type ReputationHit struct {
 	Source string `json:"source"`
 	Score  *int64 `json:"score,omitempty"`
@@ -146,9 +153,10 @@ type ReputationHit struct {
 
 // EarlierBans counts a netblock's bans before a ban, by cause.
 type EarlierBans struct {
-	Limit  int `json:"limit"`
-	Attack int `json:"attack"`
-	Admin  int `json:"admin"`
+	Limit    int `json:"limit"`
+	Attack   int `json:"attack"`
+	Admin    int `json:"admin"`
+	CrowdSec int `json:"crowdsec"`
 }
 
 // Request is a request in a ban's notes. Each text is cut to 256 bytes.
@@ -276,7 +284,8 @@ func activeBan(bans []Ban, now time.Time) *Ban {
 // BanForLimit bans netblock at now for a broken limit, with notes, and
 // returns the ban, and true. A first ban lasts LimitBanDuration. A ban
 // made within LimitBanRepeatWindow after the netblock's ban that ended
-// last, other than one for a clear sign of attack or a lifted one, lasts
+// last, other than one for a clear sign of attack or for CrowdSec's
+// decision, or a lifted one, lasts
 // repeatFactor times as long as that one. A ban that would be longer
 // than MaxBanDuration is permanent instead. If a ban on netblock is still
 // active, as when two of its requests break a limit at once, that ban is
@@ -287,7 +296,7 @@ func activeBan(bans []Ban, now time.Time) *Ban {
 func (l *Ledger) BanForLimit(
 	netblock netip.Prefix, now time.Time, notes Notes,
 ) (Ban, bool) {
-	return l.ban(netblock, now, CauseLimit, limitReason(notes), notes, true)
+	return l.ban(netblock, now, time.Time{}, CauseLimit, limitReason(notes), notes, true)
 }
 
 // WouldBanForLimit returns what BanForLimit would, without making the ban:
@@ -295,7 +304,7 @@ func (l *Ledger) BanForLimit(
 func (l *Ledger) WouldBanForLimit(
 	netblock netip.Prefix, now time.Time, notes Notes,
 ) (Ban, bool) {
-	return l.ban(netblock, now, CauseLimit, limitReason(notes), notes, false)
+	return l.ban(netblock, now, time.Time{}, CauseLimit, limitReason(notes), notes, false)
 }
 
 // BanForAttack bans netblock at now for a clear sign of attack, with
@@ -306,7 +315,7 @@ func (l *Ledger) WouldBanForLimit(
 func (l *Ledger) BanForAttack(
 	netblock netip.Prefix, now time.Time, notes Notes,
 ) (Ban, bool) {
-	return l.ban(netblock, now, CauseAttack, attackReason(notes), notes, true)
+	return l.ban(netblock, now, time.Time{}, CauseAttack, attackReason(notes), notes, true)
 }
 
 // WouldBanForAttack returns what BanForAttack would, without making the
@@ -314,12 +323,35 @@ func (l *Ledger) BanForAttack(
 func (l *Ledger) WouldBanForAttack(
 	netblock netip.Prefix, now time.Time, notes Notes,
 ) (Ban, bool) {
-	return l.ban(netblock, now, CauseAttack, attackReason(notes), notes, false)
+	return l.ban(netblock, now, time.Time{}, CauseAttack, attackReason(notes), notes,
+		false)
 }
 
-// WouldBePermanent reports whether a ban on netblock for cause, CauseLimit
-// or CauseAttack, made at now would be permanent, as BanForLimit or
-// BanForAttack would make it. It works out nothing else of the ban.
+// BanForCrowdSec bans netblock at now until expires, when CrowdSec's
+// decision on the client ends, with notes, and returns the ban, and
+// whether it made it, as BanForLimit does. Its reason is "CrowdSec's
+// decision for <scenario>", the scenario that made the decision.
+func (l *Ledger) BanForCrowdSec(
+	netblock netip.Prefix, now, expires time.Time, scenario string, notes Notes,
+) (Ban, bool) {
+	return l.ban(netblock, now, expires, CauseCrowdSec, crowdSecReason(scenario), notes,
+		true)
+}
+
+// WouldBanForCrowdSec returns what BanForCrowdSec would, without making
+// the ban: what observe mode would have done.
+func (l *Ledger) WouldBanForCrowdSec(
+	netblock netip.Prefix, now, expires time.Time, scenario string, notes Notes,
+) (Ban, bool) {
+	return l.ban(netblock, now, expires, CauseCrowdSec, crowdSecReason(scenario), notes,
+		false)
+}
+
+// WouldBePermanent reports whether a ban on netblock for cause, CauseLimit,
+// CauseAttack or CauseCrowdSec, made at now would be permanent, as
+// BanForLimit, BanForAttack or BanForCrowdSec would make it. It works out
+// nothing else of the ban. A ban for CrowdSec's decision is never
+// permanent: it ends with the decision.
 func (l *Ledger) WouldBePermanent(
 	netblock netip.Prefix, now time.Time, cause string,
 ) bool {
@@ -331,11 +363,14 @@ func (l *Ledger) WouldBePermanent(
 		held = *bans
 	}
 
-	if cause == CauseAttack {
+	switch cause {
+	case CauseAttack:
 		return l.attackExpiry(held, now).IsZero()
+	case CauseLimit:
+		return l.limitExpiry(held, now).IsZero()
+	default: // CauseCrowdSec
+		return false
 	}
-
-	return l.limitExpiry(held, now).IsZero()
 }
 
 // limitReason is the reason of a ban for a broken limit, with notes.
@@ -350,6 +385,12 @@ func attackReason(notes Notes) string {
 	return "matched the rule " + notes.RuleID
 }
 
+// crowdSecReason is the reason of a ban for CrowdSec's decision, which
+// scenario made.
+func crowdSecReason(scenario string) string {
+	return "CrowdSec's decision for " + scenario
+}
+
 // BanForAdmin bans netblock at now for an admin, with reason, until
 // expires, or for good when expires is zero, and returns the ban, whose
 // cause is CauseAdmin. Unlike BanForLimit and BanForAttack, it makes the
@@ -587,11 +628,14 @@ func (l *Ledger) holds(netblock netip.Prefix, start time.Time) bool {
 }
 
 // ban bans netblock at now for cause, with reason and notes, as
-// BanForLimit and BanForAttack describe, and returns the ban, and whether
-// it made it. Unless keep is true, the ban is not made, only returned: it
-// is the ban that would have been made.
+// BanForLimit, BanForAttack and BanForCrowdSec describe, and returns the
+// ban, and whether it made it. expires is when a ban for CauseCrowdSec
+// ends, and zero for the others, whose end the ledger works out. Unless
+// keep is true, the ban is not made, only returned: it is the ban that
+// would have been made.
 func (l *Ledger) ban(
-	netblock netip.Prefix, now time.Time, cause, reason string, notes Notes, keep bool,
+	netblock netip.Prefix, now, expires time.Time, cause, reason string, notes Notes,
+	keep bool,
 ) (Ban, bool) {
 	l.mu.Lock()
 	defer l.mu.Unlock()
@@ -613,10 +657,13 @@ func (l *Ledger) ban(
 	notes.Request = notes.Request.cut()
 	ban := Ban{Netblock: netblock, Start: now, Cause: cause, Reason: reason, Notes: notes}
 
-	if cause == CauseAttack {
+	switch cause {
+	case CauseAttack:
 		ban.Expires = l.attackExpiry(held, now)
-	} else {
+	case CauseLimit:
 		ban.Expires = l.limitExpiry(held, now)
+	default: // CauseCrowdSec
+		ban.Expires = expires
 	}
 
 	if !keep {
@@ -645,6 +692,8 @@ func earlierBans(held []Ban) EarlierBans {
 			earlier.Attack++
 		case CauseAdmin:
 			earlier.Admin++
+		case CauseCrowdSec:
+			earlier.CrowdSec++
 		}
 	}
 
@@ -738,16 +787,16 @@ func (l *Ledger) add(ban Ban) {
 // limitExpiry returns when a ban for a broken limit made at now ends, or
 // zero when it is permanent. held are the netblock's bans, none of them
 // active, of which the one that ended last, other than a ban for a clear
-// sign of attack or a lifted one, can make the new ban longer. A ban an
-// admin adds to bans.json can start after another and end before it, so
-// that one is looked for among them all.
+// sign of attack or for CrowdSec's decision, or a lifted one, can make the
+// new ban longer. A ban an admin adds to bans.json can start after
+// another and end before it, so that one is looked for among them all.
 func (l *Ledger) limitExpiry(held []Ban, now time.Time) time.Time {
 	length := l.rules.LimitBanDuration
 
 	var last *Ban
 
 	for i, ban := range held {
-		if ban.Cause != CauseAttack && ban.Lifted.IsZero() &&
+		if (ban.Cause == CauseLimit || ban.Cause == CauseAdmin) && ban.Lifted.IsZero() &&
 			(last == nil || ban.Expires.After(last.Expires)) {
 			last = &held[i]
 		}

internal/bans/crowdsec_test.go

@@ -0,0 +1,90 @@
+package bans_test
+
+import (
+	"net/netip"
+	"reflect"
+	"testing"
+	"time"
+
+	"sneak.berlin/go/smallwebwaf/internal/bans"
+)
+
+// scenario is the scenario of the tests' CrowdSec decisions.
+const scenario = "crowdsecurity/ssh-bf"
+
+func TestCrowdSecBanLastsUntilTheDecisionEnds(t *testing.T) {
+	t.Parallel()
+
+	ledger := bans.New(defaultRules())
+	netblock := netip.MustParsePrefix("203.0.113.9/32")
+	expires := midnight().Add(4 * time.Hour)
+
+	// The ban that would be made is not made.
+	would, wouldBan := ledger.WouldBanForCrowdSec(netblock, midnight(), expires,
+		scenario, bans.Notes{})
+	if !wouldBan || len(ledger.Bans(netblock)) != 0 {
+		t.Errorf("would ban %t, and the ledger holds %+v, want true and nothing",
+			wouldBan, ledger.Bans(netblock))
+	}
+
+	const reason = "CrowdSec's decision for " + scenario
+
+	ban, made := ledger.BanForCrowdSec(netblock, midnight(), expires, scenario,
+		bans.Notes{})
+	if !made || !reflect.DeepEqual(ban, would) || ban.Cause != bans.CauseCrowdSec ||
+		!ban.Expires.Equal(expires) || ban.Reason != reason ||
+		ledger.Made(bans.CauseCrowdSec) != 1 {
+		t.Errorf("made %t the ban %+v, want the one that would be made, %+v, for "+
+			"crowdsec until %s", made, ban, would, expires)
+	}
+
+	// A second decision on the netblock while the ban lasts makes no other.
+	again, made := ledger.BanForCrowdSec(netblock, midnight().Add(time.Hour),
+		expires.Add(time.Hour), scenario, bans.Notes{})
+	if made || !again.Expires.Equal(expires) || ledger.Made(bans.CauseCrowdSec) != 1 {
+		t.Errorf("made %t the ban %+v while the first lasts, want none", made, again)
+	}
+}
+
+func TestCrowdSecBanIsNeverMadePermanent(t *testing.T) {
+	t.Parallel()
+
+	ledger := bans.New(defaultRules())
+	netblock := netip.MustParsePrefix("203.0.113.9/32")
+	expires := midnight().Add(4 * time.Hour)
+	ledger.BanForCrowdSec(netblock, midnight(), expires, scenario, bans.Notes{})
+
+	// A request as the ban ends is refused, and leaves it as it is.
+	last := expires.Add(-time.Nanosecond)
+
+	held, banned, madePermanent := ledger.Check(netblock.Addr(), last)
+	if !banned || madePermanent || !held.Expires.Equal(expires) ||
+		ledger.WouldBePermanent(netblock, last, bans.CauseCrowdSec) {
+		t.Errorf("as the ban ends, banned %t with %+v, made permanent %t, want "+
+			"refused under the ban as it was", banned, held, madePermanent)
+	}
+
+	if _, banned, _ := ledger.Check(netblock.Addr(), expires); banned {
+		t.Error("the ban refuses a request once the decision has ended")
+	}
+}
+
+func TestCrowdSecBanIsCountedAndDoesNotLengthenTheNextBanForALimit(t *testing.T) {
+	t.Parallel()
+
+	ledger := bans.New(defaultRules())
+	netblock := netip.MustParsePrefix("203.0.113.9/32")
+
+	// Three times the three days would be permanent; a limit broken as the
+	// ban for CrowdSec's decision ends bans for an hour, as a first broken
+	// limit does.
+	crowdSec, _ := ledger.BanForCrowdSec(netblock, midnight(), midnight().Add(3*day),
+		scenario, bans.Notes{})
+	limit, _ := ledger.BanForLimit(netblock, crowdSec.Expires, bans.Notes{})
+
+	if limit.Expires.Sub(limit.Start) != time.Hour ||
+		limit.Notes.EarlierBans != (bans.EarlierBans{CrowdSec: 1}) {
+		t.Errorf("the ban for a limit is %+v, want one of an hour after one for crowdsec",
+			limit)
+	}
+}

internal/config/config.go

@@ -181,6 +181,13 @@ type Config struct {
 	ReputationLimitPercent int64
 	ReputationCacheTTL     time.Duration
 	ReputationTimeout      time.Duration
+	// CrowdSecDecisionsURL is where the decision list of the CrowdSec
+	// engine whose local API SWWAF_CROWDSEC_LAPI_URL names is fetched from:
+	// that URL with v1/decisions added to its path, "" while it is unset and
+	// none is. CrowdSecKey is the key the engine is asked with
+	// (SWWAF_CROWDSEC_LAPI_KEY).
+	CrowdSecDecisionsURL string
+	CrowdSecKey          string
 	// BanResponse is the status a refused client is answered with, 403
 	// or 429, or 0 to close the connection without an answer
 	// (SWWAF_BAN_RESPONSE). It answers a banned client, a request that
@@ -410,6 +417,13 @@ var (
 		"names IPv6 clients are asked about by")
 	errNotResolver = errors.New("is not an IP address with an optional port, " +
 		"such as 192.0.2.53 or [2001:db8::53]:5353")
+	errNotLAPIURL = errors.New(
+		"is not an http or https URL without a user or a fragment, " +
+			"such as http://172.17.0.1:8080")
+	errNeedsLAPIKey  = errors.New("the engine answers no request without it")
+	errLAPIKeyUnused = errors.New("it is sent only to the engine at that URL")
+	errAnotherList   = errors.New(
+		"is in SWWAF_BLOCKLIST_URLS or is SWWAF_ASN_LIMIT_PERCENT_URL too")
 )
 
 // FromEnvironment reads the settings with lookupEnv, normally
@@ -471,6 +485,8 @@ func FromEnvironment(lookupEnv func(string) (string, bool)) (*Config, error) {
 		AbuseIPDBDailyBudget: env.numberNotOff("SWWAF_ABUSEIPDB_DAILY_BUDGET", "900"),
 		ReputationCacheTTL:   env.durationNotOff("SWWAF_REPUTATION_CACHE_TTL", "24h"),
 		ReputationTimeout:    env.durationNotOff("SWWAF_REPUTATION_TIMEOUT", "2s"),
+		CrowdSecDecisionsURL: env.crowdSecDecisionsURL("SWWAF_CROWDSEC_LAPI_URL"),
+		CrowdSecKey:          env.secret("SWWAF_CROWDSEC_LAPI_KEY"),
 		BanResponse:          env.banResponse("SWWAF_BAN_RESPONSE", "403"),
 		LimitBanDuration:     env.durationNotOff("SWWAF_LIMIT_BAN_DURATION", "1h"),
 		LimitBanRepeatWindow: env.durationNotOff("SWWAF_LIMIT_BAN_REPEAT_WINDOW", "24h"),
@@ -523,6 +539,7 @@ func FromEnvironment(lookupEnv func(string) (string, bool)) (*Config, error) {
 	env.checkLookupDBPath(cfg)
 	env.checkCountriesAndLookups(cfg)
 	env.checkASNLimitPercentURL(cfg)
+	env.checkCrowdSec(cfg)
 
 	if env.err != nil {
 		return nil, env.err
@@ -835,6 +852,26 @@ func (e *environment) resolver(name string) netip.AddrPort {
 	return resolver
 }
 
+// crowdSecDecisionsURL reads the setting that is the URL of the CrowdSec
+// engine's local API, such as http://172.17.0.1:8080, and returns the URL
+// its decision list is fetched from, that URL with v1/decisions added to
+// its path, "" while it is unset or empty.
+func (e *environment) crowdSecDecisionsURL(name string) string {
+	value := e.value(name, "")
+	if value == "" {
+		return ""
+	}
+
+	lapi, err := url.Parse(value)
+	if err != nil || !isHTTPURL(lapi) {
+		e.check(name, fmt.Errorf("%q %w", value, errNotLAPIURL))
+
+		return ""
+	}
+
+	return lapi.JoinPath("v1", "decisions").String()
+}
+
 // lookupSource reads the setting that is where clients are looked up:
 // geojs, file, or off.
 func (e *environment) lookupSource(name, defaultValue string) string {
@@ -912,6 +949,26 @@ func (e *environment) checkASNLimitPercentURL(cfg *Config) {
 	}
 }
 
+// checkCrowdSec refuses SWWAF_CROWDSEC_LAPI_URL without
+// SWWAF_CROWDSEC_LAPI_KEY, the key without the URL, and a decision list
+// that is fetched as another list too.
+func (e *environment) checkCrowdSec(cfg *Config) {
+	decisionsURL := cfg.CrowdSecDecisionsURL
+
+	switch {
+	case decisionsURL != "" && cfg.CrowdSecKey == "":
+		e.check("SWWAF_CROWDSEC_LAPI_URL", fmt.Errorf(
+			"is set while SWWAF_CROWDSEC_LAPI_KEY is unset; %w", errNeedsLAPIKey))
+	case decisionsURL == "" && cfg.CrowdSecKey != "":
+		e.check("SWWAF_CROWDSEC_LAPI_KEY", fmt.Errorf(
+			"is set while SWWAF_CROWDSEC_LAPI_URL is unset; %w", errLAPIKeyUnused))
+	case decisionsURL != "" && (slices.Contains(cfg.BlocklistURLs, decisionsURL) ||
+		decisionsURL == cfg.ASNLimitPercentURL):
+		e.check("SWWAF_CROWDSEC_LAPI_URL", fmt.Errorf("gives the decision list %q, which %w",
+			decisionsURL, errAnotherList))
+	}
+}
+
 // headerNames reads a setting that is a list of header names, and
 // returns them in lower case.
 func (e *environment) headerNames(name, defaultValue string) []string {

internal/config/config_test.go

@@ -71,6 +71,8 @@ const (
 	reputationAction        = "SWWAF_REPUTATION_ACTION"
 	reputationCacheTTL      = "SWWAF_REPUTATION_CACHE_TTL"
 	reputationTimeout       = "SWWAF_REPUTATION_TIMEOUT"
+	crowdSecURL             = "SWWAF_CROWDSEC_LAPI_URL"
+	crowdSecKey             = "SWWAF_CROWDSEC_LAPI_KEY"
 	banResponse             = "SWWAF_BAN_RESPONSE"
 	limitBanDuration        = "SWWAF_LIMIT_BAN_DURATION"
 	limitBanRepeatWindow    = "SWWAF_LIMIT_BAN_REPEAT_WINDOW"
@@ -1653,6 +1655,121 @@ func TestAbuseIPDBKeyIsLoggedMasked(t *testing.T) {
 	}
 }
 
+func TestCrowdSecSettingsGiveTheDecisionListAndTheKey(t *testing.T) {
+	t.Parallel()
+
+	cfg := fromEnvironment(t, environment{})
+	if cfg.CrowdSecDecisionsURL != "" || cfg.CrowdSecKey != "" {
+		t.Errorf("by default, the decision list %q and the key %q, want neither",
+			cfg.CrowdSecDecisionsURL, cfg.CrowdSecKey)
+	}
+
+	for lapi, want := range map[string]string{
+		"http://172.17.0.1:8080":          "http://172.17.0.1:8080/v1/decisions",
+		"http://172.17.0.1:8080/":         "http://172.17.0.1:8080/v1/decisions",
+		"https://crowdsec.example/lapi/":  "https://crowdsec.example/lapi/v1/decisions",
+		"https://crowdsec.example:8443/x": "https://crowdsec.example:8443/x/v1/decisions",
+	} {
+		cfg := fromEnvironment(t, environment{crowdSecURL: lapi, crowdSecKey: token})
+		if cfg.CrowdSecDecisionsURL != want || cfg.CrowdSecKey != token {
+			t.Errorf("%s=%s gave the decision list %q and the key %q, want %s and %s",
+				crowdSecURL, lapi, cfg.CrowdSecDecisionsURL, cfg.CrowdSecKey, want, token)
+		}
+	}
+}
+
+func TestInvalidCrowdSecSettingStopsTheStartSayingWhatIsWrong(t *testing.T) {
+	t.Parallel()
+
+	const (
+		lapi       = "http://172.17.0.1:8080"
+		notLAPIURL = " is not an http or https URL without a user or a fragment, " +
+			"such as http://172.17.0.1:8080"
+		anotherList = `gives the decision list "` + lapi + `/v1/decisions", which is in ` +
+			`SWWAF_BLOCKLIST_URLS or is SWWAF_ASN_LIMIT_PERCENT_URL too`
+	)
+
+	for _, tc := range []struct {
+		name string
+		env  environment
+		want string
+	}{
+		{
+			"a URL that is not http",
+			environment{crowdSecURL: "ftp://172.17.0.1", crowdSecKey: token},
+			crowdSecURL + `: "ftp://172.17.0.1"` + notLAPIURL,
+		},
+		{
+			"a URL with a user",
+			environment{crowdSecURL: "http://bouncer@172.17.0.1:8080", crowdSecKey: token},
+			crowdSecURL + `: "http://bouncer@172.17.0.1:8080"` + notLAPIURL,
+		},
+		{
+			"the URL without the key",
+			environment{crowdSecURL: lapi},
+			crowdSecURL + ": is set while " + crowdSecKey + " is unset; the engine " +
+				"answers no request without it",
+		},
+		{
+			"the key without the URL",
+			environment{crowdSecKey: token},
+			crowdSecKey + ": is set while " + crowdSecURL + " is unset; it is sent only " +
+				"to the engine at that URL",
+		},
+		{
+			"the decision list as a blocklist too",
+			environment{
+				crowdSecURL: lapi, crowdSecKey: token,
+				blocklistURLs: "https://lists.example/drop.txt," + lapi + "/v1/decisions",
+			},
+			crowdSecURL + ": " + anotherList,
+		},
+		{
+			"the decision list as the file of AS:percent lines too",
+			environment{
+				crowdSecURL: lapi + "/", crowdSecKey: token,
+				asnLimitPercentURL: lapi + "/v1/decisions",
+			},
+			crowdSecURL + ": " + anotherList,
+		},
+		// The key itself is never shown.
+		{
+			"a key with a control character",
+			environment{crowdSecURL: lapi, crowdSecKey: token + "\r"},
+			crowdSecKey + ": holds a control character, such as the carriage return " +
+				"of a Windows line end",
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			_, err := config.FromEnvironment(tc.env.lookupEnv)
+			if err == nil || err.Error() != tc.want {
+				t.Errorf("error %v, want %s", err, tc.want)
+			}
+		})
+	}
+}
+
+func TestCrowdSecKeyIsLoggedMasked(t *testing.T) {
+	t.Parallel()
+
+	cfg := fromEnvironment(t, environment{
+		crowdSecURL: "http://172.17.0.1:8080", crowdSecKey: token,
+	})
+
+	var out bytes.Buffer
+
+	slog.New(slog.NewJSONHandler(&out, nil)).Info("starting", "settings", cfg)
+
+	logged := out.String()
+	if strings.Contains(logged, token) ||
+		!strings.Contains(logged, `"`+crowdSecKey+`":"********"`) ||
+		!strings.Contains(logged, `"`+crowdSecURL+`":"http://172.17.0.1:8080"`) {
+		t.Errorf("the key is not logged masked beside the URL: %s", logged)
+	}
+}
+
 func TestSizesAndOff(t *testing.T) {
 	t.Parallel()
 
@@ -2096,6 +2213,8 @@ func TestLogsEachSettingWithItsValue(t *testing.T) {
 		reputationAction:        "limit:25",
 		reputationCacheTTL:      defaultReputationCacheTTL,
 		reputationTimeout:       "2s",
+		crowdSecURL:             "",
+		crowdSecKey:             "",
 		banResponse:             "403",
 		limitBanDuration:        "1h",
 		limitBanRepeatWindow:    "24h",

internal/metrics/metrics.go

@@ -154,7 +154,9 @@ func New(topN int, instanceName string) *Metrics {
 func (m *Metrics) AddBansAndClients(
 	ledger *bans.Ledger, limiter *ratelimit.Limiter, now func() time.Time,
 ) {
-	for _, cause := range []string{bans.CauseLimit, bans.CauseAttack, bans.CauseAdmin} {
+	for _, cause := range []string{
+		bans.CauseLimit, bans.CauseAttack, bans.CauseAdmin, bans.CauseCrowdSec,
+	} {
 		m.registry.MustRegister(prometheus.NewCounterFunc(prometheus.CounterOpts{
 			Name:        "smallwebwaf_bans_made_total",
 			Help:        "Bans made, by cause.",
@@ -263,16 +265,16 @@ const sourceLabel = "source"
 
 // AddReputation adds the metrics of the lists fetched from URLs and of the
 // DNSBL zones, by source, each list's URL or each zone, its key masked as
-// config.MaskZoneKey masks it: the requests whose client a blocklist, a
-// zone's verdict or AbuseIPDB's score lists, which ReputationHit counts,
-// and, read from lists and dnsbl as the metrics are asked for, for a list,
-// the fetches that failed and when the copy in use was fetched, and for a
-// zone, the queries made and those that failed. It is called once, before
-// ReputationHit.
+// config.MaskZoneKey masks it: the requests whose client a blocklist, the
+// CrowdSec decision list, a zone's verdict or AbuseIPDB's score lists,
+// which ReputationHit counts, and, read from lists and dnsbl as the
+// metrics are asked for, for a list, the fetches that failed and when the
+// copy in use was fetched, and for a zone, the queries made and those that
+// failed. It is called once, before ReputationHit.
 func (m *Metrics) AddReputation(lists *reputation.Lists, dnsbl *reputation.DNSBL) {
 	m.reputationHits = counterVec("smallwebwaf_reputation_hits_total",
-		"Requests whose client a blocklist, a DNSBL zone or AbuseIPDB lists, by "+
-			"the blocklist's URL, the zone, or abuseipdb.",
+		"Requests whose client a blocklist, the CrowdSec decision list, a DNSBL "+
+			"zone or AbuseIPDB lists, by the list's URL, the zone, or abuseipdb.",
 		[]string{sourceLabel})
 	m.registry.MustRegister(m.reputationHits)
 
@@ -325,8 +327,9 @@ func (m *Metrics) AddAbuseIPDB(abuseIPDB *reputation.AbuseIPDB) {
 	)
 }
 
-// ReputationHit counts a request whose client source lists: a blocklist,
-// by its URL, a DNSBL zone, its key masked, or AbuseIPDB, abuseipdb.
+// ReputationHit counts a request whose client source lists: a blocklist
+// or the CrowdSec decision list, by its URL, a DNSBL zone, its key masked,
+// or AbuseIPDB, abuseipdb.
 func (m *Metrics) ReputationHit(source string) {
 	m.reputationHits.WithLabelValues(source).Inc()
 }

internal/proxy/bans.go

@@ -7,6 +7,7 @@ import (
 	"sneak.berlin/go/smallwebwaf/internal/alerts"
 	"sneak.berlin/go/smallwebwaf/internal/bans"
 	"sneak.berlin/go/smallwebwaf/internal/ratelimit"
+	"sneak.berlin/go/smallwebwaf/internal/reputation"
 	"sneak.berlin/go/smallwebwaf/internal/requestlog"
 	"sneak.berlin/go/smallwebwaf/internal/rules"
 )
@@ -202,6 +203,44 @@ func (rq *request) banForAttack(now time.Time, rule rules.Rule) {
 	}
 }
 
+// banForCrowdSec bans the client's netblock at now until decision,
+// CrowdSec's decision on the client, ends. In observe mode it makes no
+// ban, and raises the alert for the ban it would have made, if that alert
+// would be sent.
+func (rq *request) banForCrowdSec(now time.Time, decision reputation.Decision) {
+	netblock := rq.h.netblock(rq.client)
+	if rq.h.config.Observe && !rq.wouldAlertBan(netblock, now, bans.CauseCrowdSec) {
+		return
+	}
+
+	notes := bans.Notes{
+		ASN:        rq.line.ASN,
+		ASName:     rq.line.ASName,
+		Country:    rq.line.Country,
+		Reputation: rq.reputation,
+		Request:    rq.noted(now, rq.h.config.BanResponse),
+		Requests:   rq.netblockRequests(netblock),
+	}
+
+	if rq.h.config.Observe {
+		ban, wouldBan := rq.h.ledger.WouldBanForCrowdSec(netblock, now, decision.Expires,
+			decision.Scenario, notes)
+		if wouldBan {
+			rq.alertBan(ban)
+		}
+
+		return
+	}
+
+	ban, made := rq.h.ledger.BanForCrowdSec(netblock, now, decision.Expires,
+		decision.Scenario, notes)
+	rq.line.BanExpires = banExpires(ban)
+
+	if made {
+		rq.alertBan(ban)
+	}
+}
+
 // wouldAlertBan reports whether the alert for a ban on netblock for cause
 // made at now would be sent. In observe mode the ban the request would
 // have made is worked out only then, at most once per

internal/proxy/crowdsec_test.go

@@ -0,0 +1,181 @@
+package proxy_test
+
+import (
+	"net/http"
+	"net/netip"
+	"reflect"
+	"testing"
+	"time"
+
+	"sneak.berlin/go/smallwebwaf/internal/alerts"
+	"sneak.berlin/go/smallwebwaf/internal/bans"
+	"sneak.berlin/go/smallwebwaf/internal/proxy"
+	"sneak.berlin/go/smallwebwaf/internal/reputation"
+	"sneak.berlin/go/smallwebwaf/internal/requestlog"
+)
+
+// The CrowdSec settings, and the tests' engine, which is never asked: each
+// test puts in the copy of its decision list, at decisionsURL, that it
+// needs, as reputation.json would at start.
+const (
+	crowdSecURL  = "SWWAF_CROWDSEC_LAPI_URL"
+	crowdSecKey  = "SWWAF_CROWDSEC_LAPI_KEY"
+	lapi         = "http://crowdsec.example:8080"
+	decisionsURL = lapi + "/v1/decisions"
+	bouncerKey   = "crowdsec-key-0123456789abcdef"
+)
+
+func TestClientTheCrowdSecDecisionListListsIsBannedUntilTheDecisionEnds(t *testing.T) {
+	t.Parallel()
+
+	s, clk, server, queue := startWithAlerts(t, map[string]string{
+		crowdSecURL: lapi, crowdSecKey: bouncerKey, metricsToken: token,
+	})
+	// client had four hours left on its decision as the engine answered.
+	fetched := clk.Now()
+	loadDecisions(t, server, fetched, `[{"duration": "4h0m0s", `+
+		`"scenario": "crowdsecurity/ssh-bf", "scope": "Ip", "type": "ban", `+
+		`"value": "`+client+`"}]`)
+	expires := requestlog.FormatTime(fetched.Add(4 * time.Hour))
+
+	// Its first request is refused, and bans it until the decision ends.
+	line := s.get(client, http.StatusForbidden, requestlog.ActionBanned)
+	wantReputation(t, line, decisionsURL)
+
+	if line.BanExpires != expires {
+		t.Errorf("log line has ban_expires %q, want %s", line.BanExpires, expires)
+	}
+
+	listed := []bans.ReputationHit{{Source: decisionsURL}}
+
+	held := server.Ledger.Bans(netip.MustParsePrefix(client + "/32"))
+	if len(held) != 1 || held[0].Cause != bans.CauseCrowdSec ||
+		!held[0].Start.Equal(fetched) || !held[0].Expires.Equal(fetched.Add(4*time.Hour)) ||
+		held[0].Reason != "CrowdSec's decision for crowdsecurity/ssh-bf" ||
+		!reflect.DeepEqual(held[0].Notes.Reputation, listed) ||
+		held[0].Notes.Request.Path != "/" || held[0].Notes.Requests != 1 {
+		t.Fatalf("bans %+v, want one for crowdsec of four hours, with the list and "+
+			"the request in its notes", held)
+	}
+
+	// The listing raises a reputation_hit alert, and the ban its own.
+	waiting := queue.Snapshot().Waiting[alerts.DestinationWebhook]
+	if len(waiting) != 2 || waiting[0].Event != alerts.EventReputationHit ||
+		waiting[0].Reason != "listed by the CrowdSec decision list" ||
+		!reflect.DeepEqual(waiting[1], banAlert(alerts.EventBan, fetched, client, held[0],
+			expires)) {
+		t.Errorf("alerts waiting %+v, want a reputation_hit alert, then the ban's",
+			waiting)
+	}
+
+	// Each request while the ban lasts is refused under it, as under any
+	// ban, and once it has ended the client is let through.
+	clk.advance(4*time.Hour - time.Second)
+
+	line = s.get(client, http.StatusForbidden, requestlog.ActionBanned)
+	wantReputation(t, line)
+
+	if line.BanExpires != expires {
+		t.Errorf("log line has ban_expires %q, want %s", line.BanExpires, expires)
+	}
+
+	clk.advance(time.Second)
+	s.get(client, http.StatusOK, requestlog.ActionForward)
+
+	// The ban and the hit are counted, and the list has the metrics of any
+	// list fetched from a URL.
+	metrics := s.scrape(unplaced)
+	labels := `{instance="` + alertInstance + `",source="` + decisionsURL + `"}`
+
+	wantMetric(t, metrics, `smallwebwaf_bans_made_total{cause="crowdsec",`+
+		`instance="`+alertInstance+`"}`, 1)
+	wantMetric(t, metrics, "smallwebwaf_reputation_hits_total"+labels, 1)
+	wantMetric(t, metrics, "smallwebwaf_reputation_failures_total"+labels, 0)
+	wantMetric(t, metrics, "smallwebwaf_reputation_last_fetch_timestamp_seconds"+labels,
+		float64(fetched.Unix()))
+}
+
+func TestEndedCrowdSecDecisionNoLongerBansThoughTheCopyStillHoldsIt(t *testing.T) {
+	t.Parallel()
+
+	s, clk, server := startWithClock(t, "", map[string]string{
+		crowdSecURL: lapi, crowdSecKey: bouncerKey,
+	})
+	// 198.51.100.0/24 and 2001:db8::9 had a minute left as the engine
+	// answered.
+	fetched := clk.Now()
+	loadDecisions(t, server, fetched, `[{"duration": "1m0s", `+
+		`"scenario": "crowdsecurity/http-probing", "scope": "Range", "type": "ban", `+
+		`"value": "198.51.100.0/24"}, {"duration": "1m0s", `+
+		`"scenario": "crowdsecurity/http-probing", "scope": "Ip", "type": "ban", `+
+		`"value": "2001:db8::9"}]`)
+
+	// Just before its end, the decision bans a client in the netblock, and
+	// one on an IPv6 address bans the address's group, the /64.
+	clk.advance(time.Minute - time.Nanosecond)
+	s.get("198.51.100.7", http.StatusForbidden, requestlog.ActionBanned)
+	s.get("2001:db8::9", http.StatusForbidden, requestlog.ActionBanned)
+	s.get("2001:db8::5", http.StatusForbidden, requestlog.ActionBanned)
+
+	// Once it has ended, it bans no other client, and the bans it made end
+	// with it.
+	clk.advance(time.Nanosecond)
+
+	for _, from := range []string{"198.51.100.8", "198.51.100.7", "2001:db8::5"} {
+		wantReputation(t, s.get(from, http.StatusOK, requestlog.ActionForward))
+	}
+
+	if made := server.Ledger.Made(bans.CauseCrowdSec); made != 2 {
+		t.Errorf("%d bans made for crowdsec, want 2, on 198.51.100.7/32 and "+
+			"2001:db8::/64", made)
+	}
+
+	if held := server.Ledger.Bans(netip.MustParsePrefix("2001:db8::/64")); len(held) != 1 {
+		t.Errorf("bans of 2001:db8::/64 %+v, want one", held)
+	}
+}
+
+func TestObserveModeForwardsAClientTheCrowdSecDecisionListListsAndAlertsTheBan(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	s, clk, server, queue := startWithAlerts(t, map[string]string{
+		crowdSecURL: lapi, crowdSecKey: bouncerKey, mode: observe,
+	})
+	loadDecisions(t, server, clk.Now(), `[{"duration": "4h0m0s", `+
+		`"scenario": "crowdsecurity/ssh-bf", "scope": "Ip", "type": "ban", `+
+		`"value": "`+client+`"}]`)
+
+	line := s.get(client, http.StatusOK, requestlog.ActionForward)
+	wantWouldAction(t, line, requestlog.ActionBanned)
+	wantReputation(t, line, decisionsURL)
+
+	if held := server.Ledger.Snapshot(); len(held) != 0 {
+		t.Errorf("bans %+v, want none", held)
+	}
+
+	waiting := queue.Snapshot().Waiting[alerts.DestinationWebhook]
+	if len(waiting) != 2 || waiting[1].Event != alerts.EventBan ||
+		waiting[1].Detail["cause"] != bans.CauseCrowdSec ||
+		waiting[1].Detail["mode"] != observe {
+		t.Errorf("alerts waiting %+v, want a reputation_hit alert, then the ban alert "+
+			"marked observe", waiting)
+	}
+}
+
+// loadDecisions puts into server's lists the copy of the decision list at
+// decisionsURL, answer, the engine's answer, fetched at fetched, as
+// reputation.json would at start.
+func loadDecisions(
+	t *testing.T, server *proxy.Server, fetched time.Time, answer string,
+) {
+	t.Helper()
+
+	err := server.Lists.Load([]reputation.List{{
+		URL: decisionsURL, Tried: fetched, Fetched: fetched, Lines: []string{answer},
+	}})
+	if err != nil {
+		t.Fatalf("load the decision list: %v", err)
+	}
+}

internal/proxy/proxy.go

@@ -74,9 +74,10 @@ type Params struct {
 	Rules *rules.Files
 	// Alerts receive the alert for each ban the proxy makes or makes
 	// permanent, for each count over an anomaly threshold, for each request
-	// whose client a blocklist, a DNSBL zone or AbuseIPDB lists, and for
-	// GeoJS failing, a fetch of a list failing, a query to a DNSBL zone or
-	// a check with AbuseIPDB failing, or the day's AbuseIPDB checks used up.
+	// whose client a blocklist, the CrowdSec decision list, a DNSBL zone or
+	// AbuseIPDB lists, and for GeoJS failing, a fetch of a list failing, a
+	// query to a DNSBL zone or a check with AbuseIPDB failing, or the day's
+	// AbuseIPDB checks used up.
 	Alerts *alerts.Queue
 }
 
@@ -202,8 +203,9 @@ func newReputation(
 	cfg := params.Config
 	lists := reputation.New(reputation.Params{
 		BlocklistURLs: cfg.BlocklistURLs, Refresh: cfg.BlocklistRefresh,
-		ASNLimitPercentURL: cfg.ASNLimitPercentURL, Now: params.Now,
-		ProcessLog: params.ProcessLog, Alerts: params.Alerts,
+		ASNLimitPercentURL:   cfg.ASNLimitPercentURL,
+		CrowdSecDecisionsURL: cfg.CrowdSecDecisionsURL, CrowdSecKey: cfg.CrowdSecKey,
+		Now: params.Now, ProcessLog: params.ProcessLog, Alerts: params.Alerts,
 	})
 	dnsbl := reputation.NewDNSBL(reputation.DNSBLParams{
 		Zones: cfg.DNSBLZones, Resolver: cfg.DNSBLResolver, CacheTTL: cfg.ReputationCacheTTL,

internal/proxy/reputation.go

@@ -2,6 +2,7 @@ package proxy
 
 import (
 	"context"
+	"time"
 
 	"sneak.berlin/go/smallwebwaf/internal/alerts"
 	"sneak.berlin/go/smallwebwaf/internal/bans"
@@ -25,6 +26,22 @@ func (rq *request) blocklistDenied() bool {
 	return rq.blocklisted && rq.h.config.BlocklistAction == deny
 }
 
+// crowdSecBanned reports whether a decision of the CrowdSec decision list
+// on the client is in force at now. If one is, it notes the list, as
+// noteHit does, and bans the client until that decision ends.
+func (rq *request) crowdSecBanned(now time.Time) bool {
+	decision, listed := rq.h.lists.CrowdSecDecision(rq.client, now)
+	if !listed {
+		return false
+	}
+
+	rq.noteHit(bans.ReputationHit{Source: rq.h.config.CrowdSecDecisionsURL},
+		"listed by the CrowdSec decision list")
+	rq.banForCrowdSec(now, decision)
+
+	return true
+}
+
 // dnsblDenied notes the DNSBL zones whose verdict lists the client, as
 // noteListed does, and reports whether SWWAF_REPUTATION_ACTION, being
 // deny, refuses the request. Being limit, it lowers the client's limits

internal/proxy/request.go

@@ -226,8 +226,9 @@ func (rq *request) check(ctx context.Context) *refusal {
 // other client, SWWAF_DENY_NETS comes first, then a ban on its netblock,
 // so that a client either refuses is not looked up, then the lookup of
 // its AS number and country, then the country lists, then the blocklists,
-// then the DNSBL zones' verdicts, and then AbuseIPDB's score; a request
-// any of them refuses is not counted for the rate limits. Then come the
+// then the CrowdSec decision list, which bans the client it lists, then
+// the DNSBL zones' verdicts, and then AbuseIPDB's score; a request any of
+// them refuses is not counted for the rate limits. Then come the
 // rate limits, unless the client is in SWWAF_RATE_LIMIT_EXEMPT_NETS or the
 // request's path is exempt under SWWAF_RATE_LIMIT_EXEMPT_PATHS, so that
 // every other request is counted, each of them by the client's limit
@@ -260,6 +261,10 @@ func (rq *request) checkClient(ctx context.Context) string {
 		return requestlog.ActionDenied
 	}
 
+	if rq.crowdSecBanned(now) {
+		return requestlog.ActionBanned
+	}
+
 	if rq.dnsblDenied(ctx) || rq.abuseIPDBDenied(ctx) {
 		return requestlog.ActionDenied
 	}

internal/reputation/crowdsec_test.go

@@ -0,0 +1,428 @@
+package reputation_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/netip"
+	"reflect"
+	"strings"
+	"sync"
+	"testing"
+	"testing/synctest"
+	"time"
+
+	"sneak.berlin/go/smallwebwaf/internal/alerts"
+	"sneak.berlin/go/smallwebwaf/internal/reputation"
+)
+
+// The tests run in a synctest bubble, as those of the blocklists do, and
+// fetch the decision list from engine, a stand-in for a CrowdSec engine
+// that answers without the network.
+
+const (
+	// decisionsURL is the decision list of the tests' engine, and engineKey
+	// the key it answers.
+	decisionsURL = "http://crowdsec.example:8080/v1/decisions"
+	engineKey    = "crowdsec-key-0123456789abcdef"
+	// sshBF and probing are scenarios of the engine's decisions.
+	sshBF   = "crowdsecurity/ssh-bf"
+	probing = "crowdsecurity/http-probing"
+	// ban is the type of a decision to ban, as CrowdSec names it.
+	ban = "ban"
+)
+
+func TestCrowdSecDecisionBansItsNetblockUntilItEndsEvenWithTheEngineDown(t *testing.T) {
+	t.Parallel()
+
+	synctest.Test(t, func(t *testing.T) {
+		began := time.Now()
+		manual := "manual 'ban' from 'localhost'"
+		e := &engine{key: engineKey, decisions: []decision{
+			{"Ip", suspect, ban, manual, began.Add(6 * time.Hour)},
+			// A shorter decision on the same address, which is not the one
+			// used.
+			{"Ip", suspect, ban, sshBF, began.Add(4 * time.Hour)},
+			{"Range", "198.51.100.0/24", ban, probing, began.Add(time.Hour)},
+			{"Ip", "2001:db8::1", ban, sshBF, began.Add(2 * time.Hour)},
+			// Left out: a decision to show a captcha, and one on a country.
+			{"Ip", "192.0.2.50", "captcha", probing, began.Add(time.Hour)},
+			{"Country", "KP", ban, manual, began.Add(time.Hour)},
+		}}
+		lists := start(t, e, crowdSecParams())
+
+		for addr, want := range map[string]reputation.Decision{
+			suspect:          {Expires: began.Add(6 * time.Hour), Scenario: manual},
+			"198.51.100.0":   {Expires: began.Add(time.Hour), Scenario: probing},
+			"198.51.100.255": {Expires: began.Add(time.Hour), Scenario: probing},
+			"2001:db8::1":    {Expires: began.Add(2 * time.Hour), Scenario: sshBF},
+			"203.0.113.10":   {},
+			"198.51.101.0":   {},
+			"2001:db8::2":    {},
+			"192.0.2.50":     {},
+		} {
+			wantDecision(t, lists, addr, want)
+		}
+
+		// With the engine down, the copy kept still holds the decision on
+		// 198.51.100.0/24, which no longer bans once it has ended.
+		e.set(func(e *engine) { e.failing = true })
+		time.Sleep(time.Hour - time.Nanosecond)
+		synctest.Wait()
+		wantDecision(t, lists, "198.51.100.7",
+			reputation.Decision{Expires: began.Add(time.Hour), Scenario: probing})
+
+		time.Sleep(time.Nanosecond)
+		synctest.Wait()
+		wantDecision(t, lists, "198.51.100.7", reputation.Decision{})
+		wantDecision(t, lists, suspect,
+			reputation.Decision{Expires: began.Add(6 * time.Hour), Scenario: manual})
+	})
+}
+
+func TestCrowdSecDecisionListFetchedAgainEveryMinute(t *testing.T) {
+	t.Parallel()
+
+	synctest.Test(t, func(t *testing.T) {
+		began := time.Now()
+		e := &engine{key: engineKey, decisions: []decision{
+			{"Ip", suspect, ban, sshBF, began.Add(4 * time.Hour)},
+		}}
+		lists := start(t, e, crowdSecParams())
+		wantEngineFetches(t, e, 1)
+
+		added := reputation.Decision{Expires: began.Add(2 * time.Hour), Scenario: probing}
+
+		e.set(func(e *engine) {
+			e.decisions = append(e.decisions,
+				decision{"Ip", "203.0.113.10", ban, probing, added.Expires})
+		})
+
+		time.Sleep(time.Minute - time.Nanosecond)
+		wantEngineFetches(t, e, 1)
+		wantDecision(t, lists, "203.0.113.10", reputation.Decision{})
+
+		time.Sleep(time.Nanosecond)
+		wantEngineFetches(t, e, 2)
+		wantDecision(t, lists, "203.0.113.10", added)
+	})
+}
+
+func TestCrowdSecFailureKeepsTheLastGoodCopyAlertsOncePerCooldownAndHidesTheKey(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	for _, tc := range crowdSecFailures() {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			synctest.Test(t, func(t *testing.T) {
+				var log bytes.Buffer
+
+				began := time.Now()
+				e := &engine{key: engineKey, decisions: []decision{
+					{"Ip", suspect, ban, sshBF, began.Add(4 * time.Hour)},
+				}}
+				queue := newQueue()
+				p := crowdSecParams()
+				p.ProcessLog = slog.New(slog.NewJSONHandler(&log, nil))
+				p.Alerts = queue
+				lists := start(t, e, p)
+				kept := lists.Snapshot()
+
+				e.set(tc.fail)
+
+				// Each failure is tried again a minute after it.
+				for range 2 {
+					time.Sleep(time.Minute)
+					synctest.Wait()
+				}
+
+				wantEngineFetches(t, e, 3)
+				wantDecision(t, lists, suspect,
+					reputation.Decision{Expires: began.Add(4 * time.Hour), Scenario: sshBF})
+
+				want := kept[0]
+				want.Tried = time.Now()
+
+				if got := lists.Snapshot(); !reflect.DeepEqual(got, []reputation.List{want}) {
+					t.Errorf("lists %+v, want the first copy, last tried now, %+v", got, want)
+				}
+
+				if lists.Failures(decisionsURL) != 2 {
+					t.Errorf("%d failures, want 2", lists.Failures(decisionsURL))
+				}
+
+				// One alert for the first failure; the cooldown holds back the
+				// second.
+				wantAlert(t, queue,
+					fetchFailure(time.Now().Add(-time.Minute), decisionsURL, tc.error))
+
+				if !strings.Contains(log.String(), `"msg":"fetching a list failed",`+
+					`"url":"`+decisionsURL+`","error":"`+tc.error) {
+					t.Errorf("logged\n%s\nwant the failures", log.String())
+				}
+
+				wantKeyNotShown(t, log.String(), lists, queue)
+			})
+		})
+	}
+}
+
+// crowdSecFailure is a way for the engine to fail: fail has it answer the
+// fetches after the first so that they fail with error.
+type crowdSecFailure struct {
+	name  string
+	fail  func(e *engine)
+	error string
+}
+
+// crowdSecFailures returns the ways the engine can fail.
+func crowdSecFailures() []crowdSecFailure {
+	const notDecision = " does not give an address or a netblock and a duration, " +
+		"such as 4h0m0s"
+
+	return []crowdSecFailure{
+		{
+			"an answer other than 200",
+			func(e *engine) { e.failing = true },
+			"the server answered 503 Service Unavailable",
+		},
+		{
+			"a key the engine refuses",
+			func(e *engine) { e.key = "another-key-0123456789abcdef" },
+			"the server answered 403 Forbidden",
+		},
+		{
+			"an answer that does not read",
+			func(e *engine) { e.answer = "<html>" },
+			"read the answer: invalid character '<' looking for beginning of value",
+		},
+		{
+			"a decision to ban whose value does not read",
+			func(e *engine) {
+				e.answer = `[{"duration": "4h", "scenario": "` + sshBF + `", ` +
+					`"scope": "Ip", "type": "ban", "value": "203.0.113.300"}]`
+			},
+			"decision 1" + notDecision,
+		},
+		{
+			"a decision to ban whose duration does not read",
+			func(e *engine) {
+				e.answer = `[{"duration": "4h", "scope": "Country", "type": "ban", ` +
+					`"value": "KP"}, {"duration": "four hours", "scope": "Range", ` +
+					`"type": "ban", "value": "198.51.100.0/24"}]`
+			},
+			"decision 2" + notDecision,
+		},
+	}
+}
+
+// wantKeyNotShown checks that the engine's key is in none of what the
+// fetches leave behind: log, the process log, the alerts waiting in queue,
+// and the copies of lists, which reputation.json keeps.
+func wantKeyNotShown(
+	t *testing.T, log string, lists *reputation.Lists, queue *alerts.Queue,
+) {
+	t.Helper()
+
+	shown, err := json.Marshal([]any{lists.Snapshot(), waiting(queue)})
+	if err != nil {
+		t.Fatalf("encode: %v", err)
+	}
+
+	if strings.Contains(log+string(shown), engineKey) {
+		t.Errorf("the key is shown in\n%s\n%s", log, shown)
+	}
+}
+
+func TestCrowdSecDecisionListKeptAcrossARestartEndsWhenItsDecisionsDo(t *testing.T) {
+	t.Parallel()
+
+	synctest.Test(t, func(t *testing.T) {
+		began := time.Now()
+		e := &engine{key: engineKey, decisions: []decision{
+			{"Range", "198.51.100.0/24", ban, probing, began.Add(time.Hour)},
+		}}
+		lists := start(t, e, crowdSecParams())
+		kept := lists.Snapshot()
+
+		// Restarted half an hour later with what reputation.json keeps, and
+		// the engine down, the decision still bans, until the end it had at
+		// the fetch, half an hour on.
+		time.Sleep(30 * time.Minute)
+
+		down := &engine{key: engineKey, failing: true}
+		again := reputation.New(crowdSecParams())
+		again.SetTransport(down)
+
+		err := again.Load(kept)
+		if err != nil {
+			t.Fatalf("load: %v", err)
+		}
+
+		run(t, again)
+
+		want := reputation.Decision{Expires: began.Add(time.Hour), Scenario: probing}
+		wantDecision(t, again, "198.51.100.7", want)
+
+		time.Sleep(30*time.Minute - time.Nanosecond)
+		synctest.Wait()
+		wantDecision(t, again, "198.51.100.7", want)
+
+		time.Sleep(time.Nanosecond)
+		synctest.Wait()
+		wantDecision(t, again, "198.51.100.7", reputation.Decision{})
+	})
+}
+
+func TestLoadTakesACrowdSecListNeverFetchedAndRefusesACopyThatDoesNotRead(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	now := time.Date(2026, 10, 6, 0, 0, 0, 0, time.UTC)
+	lists := reputation.New(crowdSecParams())
+
+	// Tried, and never fetched: there is no copy to read.
+	err := lists.Load([]reputation.List{{URL: decisionsURL, Tried: now}})
+	if err != nil {
+		t.Errorf("load the list never fetched: %v", err)
+	}
+
+	err = lists.Load([]reputation.List{{
+		URL: decisionsURL, Tried: now, Fetched: now, Lines: []string{
+			`[{"duration": "4h", "scope": "Range", "type": "ban", ` +
+				`"value": "198.51.100.0/33"}]`,
+		},
+	}})
+
+	const want = "the copy of " + decisionsURL + ": decision 1 does not give an " +
+		"address or a netblock and a duration, such as 4h0m0s"
+	if err == nil || err.Error() != want {
+		t.Errorf("error %v, want %s", err, want)
+	}
+}
+
+// engine is a stand-in for the local API of a CrowdSec engine. It answers
+// a fetch of the decision list that carries its key in X-Api-Key with its
+// decisions still in force, each with the time it has left as it answers,
+// by the bubble's clock, as an engine does, or with answer while that is
+// not "". It answers 403 to a fetch without its key, as an engine does,
+// and 503 while failing. It counts the fetches.
+type engine struct {
+	mu        sync.Mutex
+	key       string
+	decisions []decision
+	answer    string
+	failing   bool
+	fetches   int
+}
+
+// decision is a decision of the engine, which ends at expires.
+type decision struct {
+	scope, value, kind, scenario string
+	expires                      time.Time
+}
+
+// RoundTrip has the engine answer req, in place of the network.
+func (e *engine) RoundTrip(req *http.Request) (*http.Response, error) {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+
+	e.fetches++
+
+	status, body := http.StatusOK, e.answer
+
+	switch {
+	case req.URL.String() != decisionsURL || req.Header.Get("X-Api-Key") != e.key:
+		status, body = http.StatusForbidden, `{"message":"access forbidden"}`
+	case e.failing:
+		status, body = http.StatusServiceUnavailable, ""
+	case body == "":
+		body = e.inForce(time.Now())
+	}
+
+	return &http.Response{
+		StatusCode: status,
+		Status:     fmt.Sprintf("%d %s", status, http.StatusText(status)),
+		Header:     http.Header{},
+		Body:       io.NopCloser(strings.NewReader(body)),
+		Request:    req,
+	}, nil
+}
+
+// inForce returns the decisions in force at now, as the engine answers
+// them: a JSON list, null for none.
+func (e *engine) inForce(now time.Time) string {
+	var answer []map[string]string
+
+	for _, d := range e.decisions {
+		if now.Before(d.expires) {
+			answer = append(answer, map[string]string{
+				"duration": d.expires.Sub(now).String(), "origin": "crowdsec",
+				"scenario": d.scenario, "scope": d.scope, "type": d.kind, "value": d.value,
+			})
+		}
+	}
+
+	body, err := json.Marshal(answer)
+	if err != nil {
+		panic(err) // a list of maps of strings always encodes
+	}
+
+	return string(body)
+}
+
+// set changes the engine with change.
+func (e *engine) set(change func(e *engine)) {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+
+	change(e)
+}
+
+// crowdSecParams returns the Params of the decision list of the tests'
+// engine, fetched with its key, by the bubble's clock, with alerts to a
+// queue that sends none.
+func crowdSecParams() reputation.Params {
+	p := params()
+	p.CrowdSecDecisionsURL = decisionsURL
+	p.CrowdSecKey = engineKey
+
+	return p
+}
+
+// wantEngineFetches waits until Run has made the fetches due, and checks
+// how many the engine has had.
+func wantEngineFetches(t *testing.T, e *engine, want int) {
+	t.Helper()
+
+	synctest.Wait()
+
+	e.mu.Lock()
+	got := e.fetches
+	e.mu.Unlock()
+
+	if got != want {
+		t.Errorf("%d fetches, want %d", got, want)
+	}
+}
+
+// wantDecision checks the decision lists says is in force on addr now,
+// the zero Decision for none.
+func wantDecision(
+	t *testing.T, lists *reputation.Lists, addr string, want reputation.Decision,
+) {
+	t.Helper()
+
+	got, listed := lists.CrowdSecDecision(netip.MustParseAddr(addr), time.Now())
+	if listed != !want.Expires.IsZero() ||
+		listed && (!got.Expires.Equal(want.Expires) || got.Scenario != want.Scenario) {
+		t.Errorf("%s has the decision %+v in force %t, want %+v", addr, got, listed, want)
+	}
+}

internal/reputation/reputation.go

@@ -1,8 +1,9 @@
 // Package reputation fetches the lists the settings name by URL: the
-// blocklists of SWWAF_BLOCKLIST_URLS, and the file of AS:percent lines
-// SWWAF_ASN_LIMIT_PERCENT_URL names. It keeps the last good copy of each,
-// whole, comment lines included, which is used while a fetch fails, and
-// when each was last tried. It also asks the DNSBL zones of
+// blocklists of SWWAF_BLOCKLIST_URLS, the file of AS:percent lines
+// SWWAF_ASN_LIMIT_PERCENT_URL names, and the decision list of the CrowdSec
+// engine SWWAF_CROWDSEC_LAPI_URL names. It keeps the last good copy of
+// each, whole, comment lines included, which is used while a fetch fails,
+// and when each was last tried. It also asks the DNSBL zones of
 // SWWAF_DNSBL_ZONES about clients, and keeps their verdicts, and checks
 // clients with AbuseIPDB, and keeps their scores and the checks spent
 // today. The state package writes all of these to reputation.json and
@@ -11,6 +12,7 @@ package reputation
 
 import (
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -32,6 +34,10 @@ const (
 	maxListBytes = 16 << 20
 	// fetchTimeout bounds one fetch of a list.
 	fetchTimeout = time.Minute
+	// crowdSecRefresh is how long after the CrowdSec decision list was last
+	// fetched or tried it is fetched again: the engine is the operator's
+	// own, and makes and ends decisions all the time.
+	crowdSecRefresh = time.Minute
 	// mappedBits is the length of ::ffff:0.0.0.0/96, the netblock of every
 	// IPv4-mapped address.
 	mappedBits = 96
@@ -43,6 +49,8 @@ var (
 	errNotNetblock   = errors.New("is not an address or a netblock, such as 192.0.2.0/24")
 	errNotASNPercent = errors.New(
 		"is not an AS number, : and a percentage, such as AS64496:50")
+	errNotDecision = errors.New(
+		"does not give an address or a netblock and a duration, such as 4h0m0s")
 )
 
 // List is a list as reputation.json holds it: the URL it is fetched from,
@@ -63,8 +71,14 @@ type Params struct {
 	// (SWWAF_ASN_LIMIT_PERCENT_URL), "" while it is unset.
 	BlocklistURLs      []string
 	ASNLimitPercentURL string
+	// CrowdSecDecisionsURL is the CrowdSec decision list, "" while
+	// SWWAF_CROWDSEC_LAPI_URL is unset, fetched with CrowdSecKey
+	// (SWWAF_CROWDSEC_LAPI_KEY).
+	CrowdSecDecisionsURL string
+	CrowdSecKey          string
 	// Refresh is how long after a list was last fetched or tried it is
-	// fetched again (SWWAF_BLOCKLIST_REFRESH).
+	// fetched again (SWWAF_BLOCKLIST_REFRESH), but for the CrowdSec decision
+	// list, which is fetched again crowdSecRefresh after.
 	Refresh time.Duration
 	// Now tells the time, normally time.Now in UTC.
 	Now func() time.Time
@@ -95,12 +109,22 @@ type list struct {
 }
 
 // entries are what the lines of a copy say: for a blocklist, the netblocks
-// it names, with the lengths among them, and for the file of AS:percent
-// lines, the percentage it gives each AS number.
+// it names, with the lengths among them, for the file of AS:percent lines,
+// the percentage it gives each AS number, and for the CrowdSec decision
+// list, the decision on each netblock that ends last, with the lengths
+// among them.
 type entries struct {
 	netblocks map[netip.Prefix]bool
 	lengths   []int
 	percents  map[string]int64
+	decisions map[netip.Prefix]Decision
+}
+
+// Decision is a decision of the CrowdSec engine to ban a netblock: when
+// it ends, and the scenario that made it, such as crowdsecurity/ssh-bf.
+type Decision struct {
+	Expires  time.Time
+	Scenario string
 }
 
 // New returns the lists, without a copy of any yet.
@@ -115,13 +139,18 @@ func New(params Params) *Lists {
 }
 
 // URLs returns the URL of every list: the blocklists' in the order
-// SWWAF_BLOCKLIST_URLS names them, then SWWAF_ASN_LIMIT_PERCENT_URL.
+// SWWAF_BLOCKLIST_URLS names them, then SWWAF_ASN_LIMIT_PERCENT_URL, then
+// the CrowdSec decision list's.
 func (l *Lists) URLs() []string {
 	urls := slices.Clone(l.params.BlocklistURLs)
 	if l.params.ASNLimitPercentURL != "" {
 		urls = append(urls, l.params.ASNLimitPercentURL)
 	}
 
+	if l.params.CrowdSecDecisionsURL != "" {
+		urls = append(urls, l.params.CrowdSecDecisionsURL)
+	}
+
 	return urls
 }
 
@@ -157,6 +186,37 @@ func (l *Lists) ASNLimitPercent(asn string) (int64, bool) {
 	return percent, listed
 }
 
+// CrowdSecDecision returns the decision of the copy of the CrowdSec
+// decision list on a netblock that holds addr and that ends last, and
+// whether it is still in force at now. A decision that has ended no
+// longer bans, even before the next fetch drops it.
+func (l *Lists) CrowdSecDecision(addr netip.Addr, now time.Time) (Decision, bool) {
+	if l.params.CrowdSecDecisionsURL == "" {
+		return Decision{}, false
+	}
+
+	l.mu.Lock()
+	defer l.mu.Unlock()
+
+	kept := l.lists[l.params.CrowdSecDecisionsURL].entries
+
+	var last Decision
+
+	for _, length := range kept.lengths {
+		netblock, err := addr.Prefix(length)
+		if err != nil {
+			continue // an IPv6 netblock's length, past an IPv4 address's 32 bits
+		}
+
+		decision := kept.decisions[netblock]
+		if decision.Expires.After(last.Expires) {
+			last = decision
+		}
+	}
+
+	return last, now.Before(last.Expires)
+}
+
 // Fetched returns when the copy in use of the list at listURL was
 // fetched, or zero while there is none.
 func (l *Lists) Fetched(listURL string) time.Time {
@@ -174,10 +234,9 @@ func (l *Lists) Failures(listURL string) int {
 	return l.lists[listURL].failures
 }
 
-// Run fetches each list once Refresh has passed since it was last fetched
-// or tried, the later of the two, until ctx is done. A list never tried is
-// fetched at once, and so is one whose last try or copy, read from
-// reputation.json, is that old.
+// Run fetches each list once it is due, as due tells, until ctx is done. A
+// list never tried is fetched at once, and so is one that is due by its
+// last try or copy read from reputation.json.
 func (l *Lists) Run(ctx context.Context) {
 	if len(l.lists) == 0 {
 		return
@@ -225,11 +284,12 @@ func (l *Lists) Load(lists []List) error {
 	found := make(map[string]entries, len(lists))
 
 	for _, kept := range lists {
-		if _, named := l.lists[kept.URL]; !named {
-			continue
+		_, named := l.lists[kept.URL]
+		if !named || kept.Fetched.IsZero() {
+			continue // dropped, or a list tried but never fetched, without a copy
 		}
 
-		read, err := l.parse(kept.URL, kept.Lines)
+		read, err := l.parse(kept.URL, kept.Lines, kept.Fetched)
 		if err != nil {
 			return fmt.Errorf("the copy of %s: %w", kept.URL, err)
 		}
@@ -245,9 +305,8 @@ func (l *Lists) Load(lists []List) error {
 	}
 
 	for _, kept := range lists {
-		read, named := found[kept.URL]
-		if named {
-			l.lists[kept.URL].kept, l.lists[kept.URL].entries = kept, read
+		if _, named := l.lists[kept.URL]; named {
+			l.lists[kept.URL].kept, l.lists[kept.URL].entries = kept, found[kept.URL]
 		}
 	}
 
@@ -276,7 +335,8 @@ func (l *Lists) fetchDue(ctx context.Context) time.Time {
 }
 
 // due returns when the list at listURL is to be fetched: Refresh after it
-// was last fetched or tried, the later of the two.
+// was last fetched or tried, the later of the two, or crowdSecRefresh
+// after for the CrowdSec decision list.
 func (l *Lists) due(listURL string) time.Time {
 	l.mu.Lock()
 	defer l.mu.Unlock()
@@ -288,6 +348,10 @@ func (l *Lists) due(listURL string) time.Time {
 		last = held.kept.Tried
 	}
 
+	if listURL == l.params.CrowdSecDecisionsURL {
+		return last.Add(crowdSecRefresh)
+	}
+
 	return last.Add(l.params.Refresh)
 }
 
@@ -298,14 +362,14 @@ func (l *Lists) due(listURL string) time.Time {
 // so that a restart waits for it: the server may have had its request.
 func (l *Lists) fetch(ctx context.Context, listURL string) {
 	lines, err := l.get(ctx, listURL)
+	now := l.params.Now()
 
 	var found entries
 	if err == nil {
-		found, err = l.parse(listURL, lines)
+		found, err = l.parse(listURL, lines, now)
 	}
 
 	cutOff := err != nil && ctx.Err() != nil
-	now := l.params.Now()
 
 	l.mu.Lock()
 
@@ -350,8 +414,10 @@ func raiseFailure(queue *alerts.Queue, reason, source string, err error) {
 	})
 }
 
-// get fetches the list at listURL, and returns its lines. An answer other
-// than 200, or a list longer than maxListBytes, is a failure.
+// get fetches the list at listURL, and returns its lines. The CrowdSec
+// decision list is fetched with CrowdSecKey in the header X-Api-Key, where
+// the engine looks for it. An answer other than 200, or a list longer
+// than maxListBytes, is a failure.
 func (l *Lists) get(ctx context.Context, listURL string) ([]string, error) {
 	ctx, cancel := context.WithTimeout(ctx, fetchTimeout)
 	defer cancel()
@@ -361,6 +427,10 @@ func (l *Lists) get(ctx context.Context, listURL string) ([]string, error) {
 		return nil, fmt.Errorf("make the request: %w", err)
 	}
 
+	if listURL == l.params.CrowdSecDecisionsURL {
+		req.Header.Set("X-Api-Key", l.params.CrowdSecKey)
+	}
+
 	res, err := l.httpClient.Do(req)
 	if err != nil {
 		// Do's error names the URL, which the log line and the alert name
@@ -393,16 +463,22 @@ func (l *Lists) get(ctx context.Context, listURL string) ([]string, error) {
 	return lines, nil
 }
 
-// parse reads the lines of the list at listURL: those of a blocklist, or
-// of the file of AS:percent lines. Anything after a ; or a # on a line is
+// parse reads the lines of the list at listURL, fetched at fetched: those
+// of a blocklist, of the file of AS:percent lines, or of the CrowdSec
+// decision list. In the first two, anything after a ; or a # on a line is
 // left out, and so is a line left blank. Any other line that does not read
 // is an error naming it by its number.
-func (l *Lists) parse(listURL string, lines []string) (entries, error) {
-	if listURL == l.params.ASNLimitPercentURL {
+func (l *Lists) parse(
+	listURL string, lines []string, fetched time.Time,
+) (entries, error) {
+	switch listURL {
+	case l.params.ASNLimitPercentURL:
 		return parsePercents(lines)
+	case l.params.CrowdSecDecisionsURL:
+		return parseDecisions(lines, fetched)
+	default:
+		return parseNetblocks(lines)
 	}
-
-	return parseNetblocks(lines)
 }
 
 // parseNetblocks reads a blocklist's lines, each an address or a netblock
@@ -486,6 +562,56 @@ func parsePercents(lines []string) (entries, error) {
 	return found, nil
 }
 
+// parseDecisions reads the lines of the CrowdSec decision list fetched at
+// fetched: the engine's answer, a JSON list of its decisions in force,
+// null while it has none. A decision of the type ban whose scope is Ip or
+// Range, as CrowdSec names them, bans its value, an address or a netblock
+// as parseNetblock reads it, until its duration, the time it had left as
+// the engine answered, has passed since fetched. Any other decision, such
+// as one to show a captcha or one on a country, is left out. A decision
+// to ban whose value or duration does not read is an error naming it by
+// its number.
+func parseDecisions(lines []string, fetched time.Time) (entries, error) {
+	var answer []struct {
+		Duration string `json:"duration"`
+		Scenario string `json:"scenario"`
+		Scope    string `json:"scope"`
+		Type     string `json:"type"`
+		Value    string `json:"value"`
+	}
+
+	err := json.Unmarshal([]byte(strings.Join(lines, "\n")), &answer)
+	if err != nil {
+		return entries{}, fmt.Errorf("read the answer: %w", err)
+	}
+
+	found := entries{decisions: map[netip.Prefix]Decision{}}
+
+	for i, decision := range answer {
+		if decision.Type != "ban" || (decision.Scope != "Ip" && decision.Scope != "Range") {
+			continue
+		}
+
+		netblock, ok := parseNetblock(decision.Value)
+
+		duration, err := time.ParseDuration(decision.Duration)
+		if !ok || err != nil {
+			return entries{}, fmt.Errorf("decision %d %w", i+1, errNotDecision)
+		}
+
+		expires := fetched.Add(duration)
+		if expires.After(found.decisions[netblock].Expires) {
+			found.decisions[netblock] = Decision{Expires: expires, Scenario: decision.Scenario}
+		}
+
+		if !slices.Contains(found.lengths, netblock.Bits()) {
+			found.lengths = append(found.lengths, netblock.Bits())
+		}
+	}
+
+	return found, nil
+}
+
 // withoutComment returns line without anything after a ; or a #, and
 // without the spaces around what is left.
 func withoutComment(line string) string {

internal/reputation/reputation_test.go

@@ -215,12 +215,7 @@ func TestFailedFetchKeepsTheLastGoodCopyAndAlertsOncePerCooldown(t *testing.T) {
 
 				// One alert for the first failure; the cooldown holds back the
 				// second.
-				wantAlert(t, queue, alerts.Alert{
-					Time:   time.Now().Add(-refresh),
-					Event:  alerts.EventSourceFailure,
-					Reason: "fetching a list failed",
-					Detail: map[string]any{"source": dropURL, "error": tc.error},
-				})
+				wantAlert(t, queue, fetchFailure(time.Now().Add(-refresh), dropURL, tc.error))
 
 				if !strings.Contains(log.String(), `"msg":"fetching a list failed",`+
 					`"url":"`+dropURL+`","error":"`+tc.error) {
@@ -535,7 +530,9 @@ func newQueue() *alerts.Queue {
 
 // start returns the lists of p, fetched through servers by Run, which runs
 // until the test ends, once Run has fetched those due at start.
-func start(t *testing.T, servers *standIn, p reputation.Params) *reputation.Lists {
+func start(
+	t *testing.T, servers http.RoundTripper, p reputation.Params,
+) *reputation.Lists {
 	t.Helper()
 
 	lists := reputation.New(p)
@@ -597,6 +594,17 @@ func waiting(queue *alerts.Queue) []alerts.Alert {
 	return queue.Snapshot().Waiting[alerts.DestinationWebhook]
 }
 
+// fetchFailure is the source_failure alert raised at the time raised for
+// a fetch of the list at listURL that failed with err.
+func fetchFailure(raised time.Time, listURL, err string) alerts.Alert {
+	return alerts.Alert{
+		Time:   raised,
+		Event:  alerts.EventSourceFailure,
+		Reason: "fetching a list failed",
+		Detail: map[string]any{"source": listURL, "error": err},
+	}
+}
+
 // wantAlert checks that want is the one alert waiting in queue, and that
 // the cooldown has held back one repeat of it.
 func wantAlert(t *testing.T, queue *alerts.Queue, want alerts.Alert) {

internal/requestlog/requestlog.go

@@ -29,7 +29,8 @@ const (
 	// over a rate limit, which bans the client.
 	ActionRateLimited = "rate_limited"
 	// ActionBanned is a request refused because a ban covers its client,
-	// or because it matched a ban rule, which bans the client.
+	// or because it matched a ban rule or the CrowdSec decision list lists
+	// its client, either of which bans the client.
 	ActionBanned = "banned"
 	// ActionRuleBlocked is a request refused because it matched a block
 	// rule.
@@ -140,8 +141,9 @@ type Line struct {
 	// minute_bytes, hour_bytes or day_bytes for a byte limit.
 	LimitHit string `json:"limit_hit,omitempty"`
 	// Reputation are the URLs of the blocklists that list the client, then
-	// the DNSBL zones whose verdict lists it, their keys masked, then
-	// abuseipdb when its score is a hit.
+	// that of the CrowdSec decision list when it does, then the DNSBL zones
+	// whose verdict lists it, their keys masked, then abuseipdb when its
+	// score is a hit.
 	Reputation []string `json:"reputation,omitempty"`
 	// Offence is the offence the request was held as, OffenceLimit.
 	Offence string `json:"offence,omitempty"`

internal/smallwebwaf/smallwebwaf_test.go

@@ -716,6 +716,80 @@ func TestBlocklistTriesAndCopiesKeptInReputationJSONAcrossRestarts(t *testing.T)
 	}
 }
 
+func TestCrowdSecDecisionListKeptInReputationJSONAcrossARestart(t *testing.T) {
+	t.Parallel()
+
+	const bouncerKey = "crowdsec-key-0123456789abcdef"
+
+	// A stand-in for the engine's local API, which bans 203.0.113.0/24 for
+	// four hours, and answers only a request with its key, while it is up.
+	down := new(atomic.Bool)
+	engine := httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			switch {
+			case r.URL.Path != "/v1/decisions" || r.Header.Get("X-Api-Key") != bouncerKey:
+				w.WriteHeader(http.StatusForbidden)
+			case down.Load():
+				w.WriteHeader(http.StatusServiceUnavailable)
+			default:
+				_, _ = io.WriteString(w, `[{"duration": "4h0m0s", "origin": "crowdsec", `+
+					`"scenario": "crowdsecurity/http-probing", "scope": "Range", `+
+					`"type": "ban", "value": "203.0.113.0/24"}]`)
+			}
+		}))
+	t.Cleanup(engine.Close)
+
+	dir := t.TempDir()
+	env := map[string]string{
+		listenAddr:                localhost + ":0",
+		upstreamURL:               startApp(t),
+		stateDir:                  dir,
+		rulesDir:                  t.TempDir(),
+		trustedProxies:            localhost + "/32",
+		"SWWAF_CROWDSEC_LAPI_URL": engine.URL,
+		"SWWAF_CROWDSEC_LAPI_KEY": bouncerKey,
+	}
+
+	// Once the list is fetched, the client's request bans it.
+	first := runUntilStopped(t, env, func(url string) {
+		for statusFrom(t, url, placed) != http.StatusForbidden {
+			time.Sleep(pollInterval)
+		}
+	})
+
+	ban := onlyBan(t, dir)
+	if ban["netblock"] != placed+"/32" || ban["cause"] != "crowdsec" ||
+		ban["reason"] != "CrowdSec's decision for crowdsecurity/http-probing" {
+		t.Errorf("bans.json holds %v, want the ban for crowdsec on %s", ban, placed)
+	}
+
+	// Restarted with the engine down, the copy kept in reputation.json bans
+	// another client in the netblock from its first request.
+	down.Store(true)
+
+	second := runUntilStopped(t, env, func(url string) {
+		wantStatus(t, url, "203.0.113.10", http.StatusForbidden)
+	})
+
+	// The key is in neither run's output, nor in a state file.
+	files := []string{"bans.json", "reputation.json", "clients.json"}
+	shown := make([]string, 0, len(files)+2)
+	shown = append(shown, first.text(), second.text())
+
+	for _, name := range files {
+		data, err := os.ReadFile(filepath.Join(dir, name)) //nolint:gosec // the test's
+		if err != nil {
+			t.Fatalf("read %s: %v", name, err)
+		}
+
+		shown = append(shown, string(data))
+	}
+
+	if all := strings.Join(shown, "\n"); strings.Contains(all, bouncerKey) {
+		t.Errorf("the key is shown in the output or the state files:\n%s", all)
+	}
+}
+
 // wantDeniedByList checks that the request log line is of a request the
 // blocklist at listURL refused.
 func wantDeniedByList(t *testing.T, line map[string]any, listURL string) {

internal/state/state.go

@@ -60,7 +60,7 @@ var (
 	errVersion = errors.New("unknown version")
 	// errMissing is for an entry without a field it needs.
 	errMissing     = errors.New("has no")
-	errCause       = errors.New("is not limit, attack or admin")
+	errCause       = errors.New("is not limit, attack, admin or crowdsec")
 	errDestination = errors.New("is not webhook, slack or ntfy")
 	errScope       = errors.New("is not client, net, asn, total or watch")
 	errWaitingList = errors.New(`waiting is a list, but now lists the alerts by ` +
@@ -647,7 +647,7 @@ func (e BanEntry) ban() bans.Ban {
 // worked out, or an expires, which would make it permanent. A permanent
 // ban's expires is null, which Bans cannot tell from a missing one, so
 // each expires is read again as written. A cause other than limit,
-// attack or admin, most likely misspelt, is refused too.
+// attack, admin or crowdsec, most likely misspelt, is refused too.
 func (f *bansFile) check(data []byte) error {
 	var written struct {
 		Bans []struct {
@@ -669,7 +669,8 @@ func (f *bansFile) check(data []byte) error {
 		case written.Bans[i].Expires == nil:
 			return missing(i, "expires")
 		case entry.Cause != "" && entry.Cause != bans.CauseLimit &&
-			entry.Cause != bans.CauseAttack && entry.Cause != bans.CauseAdmin:
+			entry.Cause != bans.CauseAttack && entry.Cause != bans.CauseAdmin &&
+			entry.Cause != bans.CauseCrowdSec:
 			return fmt.Errorf("entry %d's cause %q %w", i+1, entry.Cause, errCause)
 		}
 	}

internal/state/state_test.go

@@ -97,7 +97,8 @@ const permanentBansJSON = `{
                 "earlier_bans": {
                     "limit": 3,
                     "attack": 1,
-                    "admin": 1
+                    "admin": 1,
+                    "crowdsec": 2
                 }
             }
         }
@@ -849,8 +850,10 @@ func TestBanWithAnotherCauseStopsTheStart(t *testing.T) {
 		`{"netblock": "203.0.113.10/32", "start": "2026-10-06T00:00:00Z", `+
 		`"expires": null, "cause": "admin"}, `+
 		`{"netblock": "203.0.113.11/32", "start": "2026-10-06T00:00:00Z", `+
+		`"expires": "2026-10-06T04:00:00Z", "cause": "crowdsec"}, `+
+		`{"netblock": "203.0.113.12/32", "start": "2026-10-06T00:00:00Z", `+
 		`"expires": null, "cause": "atack"}]}`,
-		`: entry 3's cause "atack" is not limit, attack or admin`)
+		`: entry 4's cause "atack" is not limit, attack, admin or crowdsec`)
 }
 
 func TestUnknownVersionStopsTheStart(t *testing.T) {
@@ -1726,8 +1729,9 @@ func office() netip.Prefix {
 	return netip.MustParsePrefix("203.0.113.0/24")
 }
 
-// fill puts a permanent ban an admin made, a ban for a broken limit and
-// one for a clear sign of attack, clients with counts and histories,
+// fill puts a permanent ban an admin made, a ban for a broken limit, one
+// for a clear sign of attack and one for CrowdSec's decision, clients
+// with counts and histories,
 // GeoJS answers, the blocklists' last tries and the copy of one, two
 // verdicts of a DNSBL zone, and the AbuseIPDB checks spent today with two
 // scores, as filledReputationJSON holds them, and alerts
@@ -1743,6 +1747,8 @@ func fill(params state.Params) {
 	})
 	params.Ledger.BanForAttack(netip.MustParsePrefix("192.0.2.1/32"), now,
 		bans.Notes{RuleID: "env-file", Target: "path"})
+	params.Ledger.BanForCrowdSec(netip.MustParsePrefix("198.51.100.9/32"), now,
+		now.Add(4*time.Hour), "crowdsecurity/ssh-bf", bans.Notes{})
 
 	for _, c := range []string{"2001:db8::/64", "203.0.113.9/32", "192.0.2.1/32"} {
 		params.Limiter.Count(netip.MustParsePrefix(c), now, whole)
@@ -1844,7 +1850,7 @@ func permanentBan() bans.Ban {
 			},
 			Requests:    1500,
 			Refused:     3,
-			EarlierBans: bans.EarlierBans{Limit: 3, Attack: 1, Admin: 1},
+			EarlierBans: bans.EarlierBans{Limit: 3, Attack: 1, Admin: 1, CrowdSec: 2},
 		},
 	}
 }