sneak/webhooker
1
0
Fork 0
Code Issues 63 Pull Requests 7 Actions 97 Packages Projects Releases Wiki Activity

Refuse [::], 0.0.0.0, IPv6 multicast and documentation space (closes #341) #422

Merged
clawbot merged 1 commits from issue-341-ipv6-unspecified-blocklist into next 2026-10-02 11:22:31 +02:00
Conversation 5 Commits 1 Files Changed 6
+185 -62
6 changed files with 185 additions and 62 deletions
Download Patch File Download Diff File Expand all files Collapse all files
README.md
+41 -28
View File
@@ -158,19 +158,20 @@ WireServer, which serves an Azure VM its credentials. Because it is a
public address, listing it in `ALLOWED_EGRESS_CIDRS` reopens it.
That is all the default blocklist covers: the IPv4 private and reserved
ranges; of IPv6, only loopback (`::1`), unique local addresses
(`fc00::/7`) and link-local addresses (`fe80::/10`); and certain public
addresses. A public address belongs on the default blocklist only if it
hands credentials, user data or bootstrap material to whatever can reach
it, without the caller presenting anything. A provider's other public
addresses are not refused. IBM Cloud, for example, serves its package
mirrors, time servers and object storage on `161.26.0.0/16`, and the
private endpoints of its own cloud services on `166.8.0.0/14`. Neither
range hands out credentials that way: the token service among those
endpoints issues a token only in exchange for something the caller
presents, such as an API key. Reaching these services can be a
legitimate delivery, and every cloud has some, so a partial list would
promise coverage it does not give.
ranges; of IPv6, only loopback (`::1`), the unspecified address (`::`),
unique local addresses (`fc00::/7`), link-local addresses (`fe80::/10`),
multicast (`ff00::/8`) and documentation space (`2001:db8::/32`); and
certain public addresses. A public address belongs on the default
blocklist only if it hands credentials, user data or bootstrap material
to whatever can reach it, without the caller presenting anything. A
provider's other public addresses are not refused. IBM Cloud, for
example, serves its package mirrors, time servers and object storage on
`161.26.0.0/16`, and the private endpoints of its own cloud services on
`166.8.0.0/14`. Neither range hands out credentials that way: the token
service among those endpoints issues a token only in exchange for
something the caller presents, such as an API key. Reaching these
services can be a legitimate delivery, and every cloud has some, so a
partial list would promise coverage it does not give.
That default is also inconvenient for the thing webhooker is mostly
for: taking a public webhook and forwarding it to something on your own
@@ -210,16 +211,16 @@ Two things this setting cannot do:
the list is always an allowlist; an empty list (the default) means
every private and reserved range stays refused. Note that
`0.0.0.0/0` gets you most of the way there anyway, per above.
- **It cannot open link-local, or a cloud metadata endpoint at a
non-public address that discloses credentials or user data.** An
address is on the list below when it is not a public address and both
of these hold: the provider fixes it, so it cannot collide with
anything you run; and reaching it hands out credentials, user data or
bootstrap material. Those stay blocked no matter what you list,
including when you list them outright or list a supernet such as
`0.0.0.0/0`, `::/0`, `fd00::/8` or `100.64.0.0/10`. Treat this as best
effort rather than a guarantee — it is a hand-maintained list and the
caveat below the table applies:
- **It cannot open link-local, the unspecified addresses, or a cloud
metadata endpoint at a non-public address that discloses credentials
or user data.** A metadata address is on the list below when it is not
a public address and both of these hold: the provider fixes it, so it
cannot collide with anything you run; and reaching it hands out
credentials, user data or bootstrap material. Those stay blocked no
matter what you list, including when you list them outright or list a
supernet such as `0.0.0.0/0`, `::/0`, `fd00::/8` or `100.64.0.0/10`.
Treat this as best effort rather than a guarantee — it is a
hand-maintained list and the caveat below the table applies:
| Blocked unconditionally | What it is |
| ----------------------- | ---------- |
@@ -233,14 +234,25 @@ Two things this setting cannot do:
| `fd00:a9fe:a9fe::1/128` | Linode/Akamai metadata over IPv6 |
| `100.100.100.200/32` | Alibaba Cloud metadata, inside CGNAT |
| `192.0.0.192/32` | Oracle Cloud Classic metadata |
| `0.0.0.0/32` | IPv4 unspecified address, which reaches this host's loopback on Linux |
| `::/128` | IPv6 unspecified address, which reaches this host's loopback on Linux |
| `::a9fe:a9fe/128` | `169.254.169.254` as an IPv4-compatible IPv6 address |
| `64:ff9b::a9fe:a9fe/128` | `169.254.169.254` behind the NAT64 well-known prefix |
The IPv4-mapped form `::ffff:169.254.169.254` is covered by the
`169.254.0.0/16` entry. Reaching any of these is credential or
user-data theft rather than delivery to an internal service. Every
entry outside the two link-local blocks is a single address, so
blocking it costs you nothing else on the network around it.
`169.254.0.0/16` entry. Reaching any of these but the two unspecified
addresses is credential or user-data theft rather than delivery to an
internal service. Every entry outside the two link-local blocks is a
single address, so blocking it costs you nothing else on the network
around it.
The unspecified addresses `0.0.0.0` and `::` hand out nothing
themselves, but no host can have either, and on Linux a connection to
one reaches this host's own loopback. They are listed so that an
allowlist reaches loopback only through an entry that covers a loopback
address, such as `127.0.0.0/8`, `::1` or `0.0.0.0/0`, never through one
that covers only `0.0.0.0` or `::`; `0.0.0.0/8`, for example, does not
open loopback.
The six ULA entries, all inside `fd00::/8`, are why this matters in
practice: `fd00::/8` is an ordinary block to allowlist for your own
@@ -3093,7 +3105,8 @@ check, see [The login endpoint](#the-login-endpoint).
route through a single decision function, so they cannot disagree
about a destination. An operator can permit specific blocks with
[`ALLOWED_EGRESS_CIDRS`](#allowing-egress-to-your-own-network); the
guard cannot be switched off, and link-local plus a
guard cannot be switched off, and link-local, the unspecified
addresses `0.0.0.0` and `::`, and a
[pinned set](#allowing-egress-to-your-own-network) of known cloud
metadata endpoints — several of which are ULAs outside link-local —
stay blocked whatever is listed, though listing `0.0.0.0/0` or
internal/config/config.go
+7 -6
View File
@@ -196,12 +196,13 @@ type Config struct {
// otherwise refuse. The guard itself is always on: there is no
// setting that disables SSRF protection, and delivery's
// alwaysBlockedNetworks stays blocked no matter what is listed
// here. That set is link-local plus the cloud metadata
// endpoints outside it that disclose credentials or user data
// at a provider-fixed, non-public address; it is not
// exhaustive of every cloud's metadata address. See
// alwaysBlockedNetworks for the authoritative list and the
// criterion it is built from.
// here. That set is link-local, the unspecified addresses
// 0.0.0.0 and ::, and the cloud metadata endpoints outside
// link-local that disclose credentials or user data at a
// provider-fixed, non-public address; it is not exhaustive of
// every cloud's metadata address. See
// alwaysBlockedNetworks for the authoritative list and why
// each entry is on it.
AllowedEgressCIDRs []netip.Prefix
params *ConfigParams
internal/delivery/ssrf.go
+57 -13
View File
@@ -37,8 +37,8 @@ var (
"blocked cloud metadata address",
)
errBlockedMetadata = errors.New(
"blocked link-local or cloud instance metadata " +
"address: ALLOWED_EGRESS_CIDRS cannot open it",
"blocked link-local, cloud instance metadata or " +
"unspecified address: ALLOWED_EGRESS_CIDRS cannot open it",
)
errInvalidScheme = errors.New(
"only http and https are allowed",
@@ -72,14 +72,17 @@ var blockedNetworks []*net.IPNet
var blockedPublicNetworks []*net.IPNet
// alwaysBlockedNetworks are the ranges no configuration can
// open: the link-local blocks and the cloud instance metadata
// endpoints that live outside them. Reaching one is credential
// or user-data theft rather than delivery to an internal
// service, so a supplied CIDR that covers such an address still
// leaves it blocked.
// open, so a supplied CIDR that covers one still leaves it
// blocked. An entry is here for one of two reasons: it is a
// metadata endpoint (the link-local blocks and the cloud
// instance metadata endpoints that live outside them), or it is
// an unspecified address. Reaching a metadata endpoint is
// credential or user-data theft rather than delivery to an
// internal service.
//
// Inclusion criterion — an address belongs here only if BOTH
// hold, and every entry below satisfies both:
// Inclusion criterion for metadata endpoints — one belongs here
// only if BOTH hold, and every metadata entry below satisfies
// both:
//
// 1. It is a fixed address assigned by the provider, or a
// range reserved by IANA — never one the operator chose.
@@ -90,8 +93,8 @@ var blockedPublicNetworks []*net.IPNet
// not cheaply rotated.
//
// Both halves are load-bearing, so use them to refuse a
// candidate and say why. An endpoint disclosing only the
// operator's own inventory (instance id, region, disks, NICs)
// metadata candidate and say why. An endpoint disclosing only
// the operator's own inventory (instance id, region, disks, NICs)
// fails (2): letting a delivery target reach the operator's own
// infrastructure is the feature ALLOWED_EGRESS_CIDRS exists to
// provide. But (2) is not "IAM credentials only" either —
@@ -112,6 +115,15 @@ var blockedPublicNetworks []*net.IPNet
// This is a criterion, not an enumeration of every metadata
// address in existence.
//
// The unspecified addresses 0.0.0.0 and :: are here for a
// separate reason: they disclose nothing, but no host can have
// either, and on Linux a connection to one reaches this host's
// own loopback. Listing them means an allowlist reaches loopback
// only through an entry that covers a loopback address
// (127.0.0.0/8, ::1/128, 0.0.0.0/0), never through one that
// covers only 0.0.0.0 or :: (0.0.0.0/8, for example). Nothing
// else lives at either address, so refusing them costs nothing.
//
// Every entry is either already in blockedNetworks — this list is
// what makes it unconditional — or an alternate encoding of
// 169.254.169.254 that Contains does not match against
@@ -131,23 +143,46 @@ var alwaysBlockedNetworks []*net.IPNet
//nolint:gochecknoinits // init is the idiomatic way to parse CIDRs once at startup
func init() {
blockedNetworks = mustParseCIDRs([]string{
// IPv4 loopback.
"127.0.0.0/8",
// RFC 1918 private network.
"10.0.0.0/8",
// RFC 1918 private network.
"172.16.0.0/12",
// RFC 1918 private network.
"192.168.0.0/16",
// IPv4 link-local.
"169.254.0.0/16",
// "This network", holding the IPv4 unspecified address 0.0.0.0.
"0.0.0.0/8",
// Carrier-grade NAT shared address space.
"100.64.0.0/10",
// IETF protocol assignments.
"192.0.0.0/24",
// IPv4 documentation (TEST-NET-1).
"192.0.2.0/24",
// Benchmarking.
"198.18.0.0/15",
// IPv4 documentation (TEST-NET-2).
"198.51.100.0/24",
// IPv4 documentation (TEST-NET-3).
"203.0.113.0/24",
// IPv4 multicast.
"224.0.0.0/4",
// Reserved, including the broadcast address.
"240.0.0.0/4",
// IPv6 loopback.
"::1/128",
// IPv6 unspecified address.
"::/128",
// IPv6 unique local addresses.
"fc00::/7",
// IPv6 link-local.
"fe80::/10",
// IPv6 multicast.
"ff00::/8",
// IPv6 documentation.
"2001:db8::/32",
})
blockedPublicNetworks = mustParseCIDRs([]string{
@@ -207,6 +242,14 @@ func init() {
// allowlist from opening it.
"192.0.0.192/32",
// The unspecified addresses, each of which reaches this
// host's loopback on Linux.
//
// IPv4 unspecified address, inside the blocked 0.0.0.0/8.
"0.0.0.0/32",
// IPv6 unspecified address.
"::/128",
// 169.254.169.254 as an IPv4-compatible IPv6 address.
"::a9fe:a9fe/128",
// 169.254.169.254 behind the NAT64 well-known prefix.
@@ -343,8 +386,9 @@ func (g *Guard) allows(ip net.IP) bool {
// The order is the policy:
//
// 1. alwaysBlockedNetworks is refused before the allowlist is
// consulted, so no configured CIDR reaches link-local or a
// cloud metadata endpoint at a non-public address.
// consulted, so no configured CIDR reaches link-local, a
// cloud metadata endpoint at a non-public address, or an
// unspecified address.
// 2. The allowlist is consulted next, so a listed private
// network, or a listed public address on the default
// blocklist, becomes reachable.
internal/delivery/ssrf_allowlist_test.go
+39 -11
View File
@@ -168,12 +168,13 @@ func TestGuardAllowlist_UnlistedPrivateStillRefused(t *testing.T) {
// TestGuardAllowlist_MetadataAlwaysRefused is the load-bearing
// case: cloud instance metadata endpoints are credential theft
// rather than delivery to an internal service, so no allowlist
// reaches one. Every guard below names a CIDR that covers its
// target — including 0.0.0.0/0, ::/0, and the ordinary ULA and
// CGNAT blocks an operator would really list — and the address
// must stay refused anyway, on both the validation and the
// delivery path.
// rather than delivery to an internal service, and the
// unspecified addresses 0.0.0.0 and :: reach this host's loopback
// on Linux, so no allowlist reaches any of them. Every guard
// below names a CIDR that covers its target — including
// 0.0.0.0/0, ::/0, and the ordinary ULA and CGNAT blocks an
// operator would really list — and the address must stay
// refused anyway, on both the validation and the delivery path.
func TestGuardAllowlist_MetadataAlwaysRefused(t *testing.T) {
t.Parallel()
@@ -219,15 +220,17 @@ type metadataAlwaysRefusedCase struct {
}
// metadataAlwaysRefusedCases enumerates every unconditionally
// blocked address together with an allowlist entry that would
// otherwise reach it. Split by family of address only to stay
// under the function-length limit.
// blocked address (link-local, the cloud metadata endpoints and
// the unspecified addresses) together with an allowlist entry
// that would otherwise reach it. Split by family of address only
// to stay under the function-length limit.
func metadataAlwaysRefusedCases() []metadataAlwaysRefusedCase {
cases := linkLocalRefusedCases()
cases = append(cases, ulaMetadataRefusedCases()...)
cases = append(cases, ipv4MetadataRefusedCases()...)
cases = append(cases, encodedMetadataRefusedCases()...)
return append(cases, encodedMetadataRefusedCases()...)
return append(cases, unspecifiedRefusedCases()...)
}
// linkLocalRefusedCases covers the link-local blocks, including
@@ -367,6 +370,23 @@ func encodedMetadataRefusedCases() []metadataAlwaysRefusedCase {
}
}
// unspecifiedRefusedCases covers the unspecified addresses, each
// of which reaches this host's loopback on Linux.
func unspecifiedRefusedCases() []metadataAlwaysRefusedCase {
return []metadataAlwaysRefusedCase{
{
name: "IPv4 unspecified address under 0.0.0.0/0",
allow: allowAllIPv4,
target: "http://0.0.0.0:8080/hook",
},
{
name: "IPv6 unspecified address under ::/0",
allow: allowAllIPv6,
target: "http://[::]:8080/hook",
},
}
}
// TestGuardAllowlist_PublicUnaffected asserts the allowlist does
// not narrow anything: public addresses were reachable before it
// existed and stay reachable, whether or not a list is set.
@@ -524,6 +544,10 @@ func TestAlwaysBlockedNetworks_PinnedSet(t *testing.T) {
// Oracle Cloud Classic metadata, inside the blocked
// 192.0.0.0/24.
"192.0.0.192/32",
// The IPv4 and IPv6 unspecified addresses, each of
// which reaches this host's loopback on Linux.
"0.0.0.0/32",
"::/128",
// 169.254.169.254 as an IPv4-compatible IPv6 address.
"::a9fe:a9fe/128",
// 169.254.169.254 behind the NAT64 well-known prefix.
@@ -556,7 +580,8 @@ func TestDefaultBlocklist_PinnedSet(t *testing.T) {
{cidr: "172.16.0.0/12", reopenable: true},
{cidr: "192.168.0.0/16", reopenable: true},
{cidr: linkLocalIPv4, reopenable: false},
{cidr: "0.0.0.0/8", reopenable: true},
// Its first address, 0.0.0.0, is in the unconditional set.
{cidr: "0.0.0.0/8", reopenable: false},
{cidr: "100.64.0.0/10", reopenable: true},
{cidr: "192.0.0.0/24", reopenable: true},
{cidr: "192.0.2.0/24", reopenable: true},
@@ -566,8 +591,11 @@ func TestDefaultBlocklist_PinnedSet(t *testing.T) {
{cidr: "224.0.0.0/4", reopenable: true},
{cidr: "240.0.0.0/4", reopenable: true},
{cidr: "::1/128", reopenable: true},
{cidr: "::/128", reopenable: false},
{cidr: "fc00::/7", reopenable: true},
{cidr: "fe80::/10", reopenable: false},
{cidr: "ff00::/8", reopenable: true},
{cidr: "2001:db8::/32", reopenable: true},
{cidr: "168.63.129.16/32", public: true, reopenable: true},
}
internal/delivery/ssrf_test.go
+36
View File
@@ -101,6 +101,42 @@ func TestValidateTargetURL_Blocked(t *testing.T) {
}
}
// TestDefaultGuard_RefusesUnspecifiedMulticastAndDocumentation
// covers the unspecified addresses and the IPv6 multicast and
// documentation ranges: with no allowlist set, each is refused
// both when a target is created and when a delivery dials it.
func TestDefaultGuard_RefusesUnspecifiedMulticastAndDocumentation(
t *testing.T,
) {
t.Parallel()
guard := delivery.NewTestGuard()
targets := []string{
// The unspecified addresses. On Linux a connection to
// either reaches this host's loopback.
"http://0.0.0.0:8080/hook",
"http://[::]:8080/hook",
// IPv6 multicast, all nodes.
"http://[ff02::1]/hook",
// IPv6 documentation.
"http://[2001:db8::1]/hook",
}
for _, target := range targets {
t.Run(target, func(t *testing.T) {
t.Parallel()
require.Error(t,
guard.ValidateTargetURL(context.Background(), target),
"%s must be refused at target creation", target,
)
assertDialRefused(t, guard, target)
})
}
}
func TestValidateTargetURL_Allowed(t *testing.T) {
t.Parallel()
internal/handlers/source_management.go
+5 -4
View File
@@ -1560,10 +1560,11 @@ func (h *Handlers) validateTargetURL(
msg := "Invalid target URL: " + err.Error()
// Only a private or reserved address's refusal says how
// to allow it. Metadata refusals never do: link-local and
// the other unconditional metadata addresses cannot be
// opened, and the default blocklist's public addresses,
// which listing does open, hand out credentials.
// to allow it. Other refusals never do: link-local, the
// unspecified addresses and the unconditional metadata
// addresses cannot be opened, and the default
// blocklist's public addresses, which listing does open,
// hand out credentials.
if errors.Is(err, delivery.ErrBlockedPrivateOrReservedIP) {
msg += ". Private and reserved addresses are refused " +
"by default; the server's ALLOWED_EGRESS_CIDRS " +