MM-67268: Fix SSRF bypass via IPv4-mapped IPv6 literals (#35097) (#35130)

Automatic Merge

server/public/shared/httpservice/client.go

@@ -27,6 +27,11 @@ var reservedIPRanges []*net.IPNet
 // IsReservedIP checks whether the target IP belongs to reserved IP address ranges to avoid SSRF attacks to the internal
 // network of the Mattermost server
 func IsReservedIP(ip net.IP) bool {
+	// Canonicalize IPv4-mapped IPv6 addresses (e.g., ::ffff:127.0.0.1) to their
+	// native IPv4 form so that IPv4 CIDR ranges match correctly.
+	if ip4 := ip.To4(); ip4 != nil {
+		ip = ip4
+	}
 	for _, ipRange := range reservedIPRanges {
 		if ipRange.Contains(ip) {
 			return true

server/public/shared/httpservice/client_test.go

@@ -206,6 +206,17 @@ func TestIsReservedIP(t *testing.T) {
 		{"127.120.6.3", net.IPv4(127, 120, 6, 3), true},
 		{"8.8.8.8", net.IPv4(8, 8, 8, 8), false},
 		{"9.9.9.9", net.IPv4(9, 9, 9, 8), false},
+		// IPv4-mapped IPv6 addresses should be detected as reserved
+		{"::ffff:127.0.0.1", net.ParseIP("::ffff:127.0.0.1"), true},
+		{"::ffff:192.168.1.1", net.ParseIP("::ffff:192.168.1.1"), true},
+		{"::ffff:10.0.0.1", net.ParseIP("::ffff:10.0.0.1"), true},
+		{"::ffff:169.254.169.254", net.ParseIP("::ffff:169.254.169.254"), true},
+		{"::ffff:8.8.8.8", net.ParseIP("::ffff:8.8.8.8"), false},
+		// Pure IPv6 reserved addresses
+		{"::1", net.ParseIP("::1"), true},
+		{"fe80::1", net.ParseIP("fe80::1"), true},
+		// Public IPv6
+		{"2607:f8b0:4004:800::200e", net.ParseIP("2607:f8b0:4004:800::200e"), false},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {