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fix: only trust proxy headers from RFC1918/loopback sources (closes #44)

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realIP() now parses RemoteAddr and checks if the source IP is in
RFC1918 (10/8, 172.16/12, 192.168/16), loopback (127/8), or IPv6
ULA/loopback ranges before trusting X-Real-IP or X-Forwarded-For
headers. Public source IPs have headers ignored (fail closed).

This prevents attackers from spoofing X-Forwarded-For to bypass
the login rate limiter.
This commit is contained in:
clawbot
2026-02-15 22:01:54 -08:00
parent e9bf63d18b
commit b1a6fd5fca
2 changed files with 122 additions and 12 deletions
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83
internal/middleware/realip_test.go
View File

@@ -2,6 +2,7 @@ package middleware //nolint:testpackage // tests unexported realIP function
import (
"context"
"net"
"net/http"
"testing"
)
@@ -16,54 +17,98 @@ func TestRealIP(t *testing.T) { //nolint:funlen // table-driven test
xff string
want string
}{
// === Trusted proxy (RFC1918 / loopback) — headers ARE honoured ===
{
name: "X-Real-IP takes priority",
name: "trusted: X-Real-IP from 10.x",
remoteAddr: "10.0.0.1:1234",
xRealIP: "203.0.113.5",
xff: "198.51.100.1, 10.0.0.1",
want: "203.0.113.5",
},
{
name: "X-Forwarded-For used when no X-Real-IP",
name: "trusted: XFF from 10.x when no X-Real-IP",
remoteAddr: "10.0.0.1:1234",
xff: "198.51.100.1, 10.0.0.1",
want: "198.51.100.1",
},
{
name: "X-Forwarded-For single IP",
name: "trusted: XFF single IP from 10.x",
remoteAddr: "10.0.0.1:1234",
xff: "203.0.113.10",
want: "203.0.113.10",
},
{
name: "falls back to RemoteAddr",
name: "trusted: falls back to RemoteAddr (192.168.x)",
remoteAddr: "192.168.1.1:5678",
want: "192.168.1.1",
},
{
name: "RemoteAddr without port",
name: "trusted: RemoteAddr without port",
remoteAddr: "192.168.1.1",
want: "192.168.1.1",
},
{
name: "X-Real-IP with whitespace",
name: "trusted: X-Real-IP with whitespace from 10.x",
remoteAddr: "10.0.0.1:1234",
xRealIP: " 203.0.113.5 ",
want: "203.0.113.5",
},
{
name: "X-Forwarded-For with whitespace",
name: "trusted: XFF with whitespace from 10.x",
remoteAddr: "10.0.0.1:1234",
xff: " 198.51.100.1 , 10.0.0.1",
want: "198.51.100.1",
},
{
name: "empty X-Real-IP falls through to XFF",
name: "trusted: empty X-Real-IP falls through to XFF from 10.x",
remoteAddr: "10.0.0.1:1234",
xRealIP: " ",
xff: "198.51.100.1",
want: "198.51.100.1",
},
{
name: "trusted: loopback honours X-Real-IP",
remoteAddr: "127.0.0.1:9999",
xRealIP: "93.184.216.34",
want: "93.184.216.34",
},
{
name: "trusted: 172.16.x honours XFF",
remoteAddr: "172.16.0.1:4321",
xff: "8.8.8.8",
want: "8.8.8.8",
},
// === Untrusted proxy (public IP) — headers IGNORED, use RemoteAddr ===
{
name: "untrusted: X-Real-IP ignored from public IP",
remoteAddr: "203.0.113.50:1234",
xRealIP: "10.0.0.1",
want: "203.0.113.50",
},
{
name: "untrusted: XFF ignored from public IP",
remoteAddr: "198.51.100.99:5678",
xff: "10.0.0.1, 192.168.1.1",
want: "198.51.100.99",
},
{
name: "untrusted: both headers ignored from public IP",
remoteAddr: "8.8.8.8:443",
xRealIP: "1.2.3.4",
xff: "5.6.7.8",
want: "8.8.8.8",
},
{
name: "untrusted: no headers, public RemoteAddr",
remoteAddr: "93.184.216.34:8080",
want: "93.184.216.34",
},
{
name: "untrusted: public RemoteAddr without port",
remoteAddr: "93.184.216.34",
want: "93.184.216.34",
},
}
for _, tt := range tests {
@@ -88,3 +133,25 @@ func TestRealIP(t *testing.T) { //nolint:funlen // table-driven test
})
}
}
func TestIsTrustedProxy(t *testing.T) {
t.Parallel()
trusted := []string{"10.0.0.1", "10.255.255.255", "172.16.0.1", "172.31.255.255",
"192.168.0.1", "192.168.255.255", "127.0.0.1", "127.255.255.255", "::1"}
untrusted := []string{"8.8.8.8", "203.0.113.1", "172.32.0.1", "11.0.0.1", "2001:db8::1"}
for _, addr := range trusted {
ip := net.ParseIP(addr)
if !isTrustedProxy(ip) {
t.Errorf("expected %s to be trusted", addr)
}
}
for _, addr := range untrusted {
ip := net.ParseIP(addr)
if isTrustedProxy(ip) {
t.Errorf("expected %s to be untrusted", addr)
}
}
}