fix(sec): webhook SSRF-guard через Dialer.Control (закрытие DNS-rebinding TOCTOU)

internal/notify/webhook.go

@@ -9,6 +9,8 @@ import (
 	"net"
 	"net/http"
 	"net/url"
+	"syscall"
+	"time"
 )
 
 // Webhook delivers notifications as a JSON POST of the Event to a
@@ -16,17 +18,30 @@ import (
 // unused (reserved for future request signing) and is never logged.
 //
 // The destination URL is project-controlled (any project owner can set it),
-// so it is treated as untrusted input: isAllowedURL blocks requests to
-// loopback/private/link-local/unspecified addresses to prevent SSRF against
-// internal services and cloud metadata endpoints (e.g. 169.254.169.254).
-// Redirects are not followed, since a redirect response could otherwise be
-// used to bypass the destination check.
+// so it is treated as untrusted input. Two layers guard against SSRF:
+//
+//  1. isAllowedURL is a pre-request fast-fail check on the URL's scheme and
+//     (resolved) hostname.
+//  2. HTTP's Transport, when built via newWebhookTransport, wires a
+//     net.Dialer.Control that re-checks the actual "ip:port" being dialed for
+//     every connection net/http opens — including the DNS resolution
+//     http.Client.Do performs internally, independent of (1).
+//
+// Layer (2) is the source of truth: DNS answers are attacker-influenceable
+// (an attacker with authoritative DNS and a low TTL can answer a public IP to
+// a pre-request lookup and a private/loopback IP to the actual connection —
+// DNS rebinding). Relying on (1) alone leaves that TOCTOU window open; (2)
+// closes it because it inspects the address the connection is actually made
+// to, not a name. Redirects are not followed, since a redirect response
+// could otherwise be used to bypass the destination checks.
 type Webhook struct {
 	HTTP *http.Client
 
-	// allowPrivate disables the SSRF guard. It exists only so tests can
-	// exercise Send happy-paths against httptest servers, which listen on
-	// loopback. Production Dispatchers (NewDispatcher) must never set this.
+	// allowPrivate disables the isAllowedURL pre-check. It exists only so
+	// tests can exercise Send happy-paths against httptest servers, which
+	// listen on loopback. Production Dispatchers (NewDispatcher) must never
+	// set this; they also wire a Transport whose Control func enforces the
+	// same guard at dial time regardless of this flag.
 	allowPrivate bool
 }
 
@@ -61,14 +76,18 @@ func isAllowedURL(rawurl string) error {
 	}
 
 	for _, ip := range ips {
-		if isDisallowedIP(ip) {
+		if isBlockedIP(ip) {
 			return errors.New("webhook: destination not allowed")
 		}
 	}
 	return nil
 }
 
-func isDisallowedIP(ip net.IP) bool {
+// isBlockedIP reports whether ip must never be connected to: loopback,
+// private (RFC1918 etc.), link-local, unspecified, or multicast. Used both
+// by isAllowedURL's pre-request check and by dialControl's per-connection
+// check.
+func isBlockedIP(ip net.IP) bool {
 	return ip.IsLoopback() ||
 		ip.IsPrivate() ||
 		ip.IsLinkLocalUnicast() ||
@@ -77,6 +96,50 @@ func isDisallowedIP(ip net.IP) bool {
 		ip.IsMulticast()
 }
 
+// dialControl returns a net.Dialer.Control function enforcing the SSRF guard
+// on the literal address ("ip:port") that net/http is about to connect to.
+// It runs after any DNS resolution net/http performs internally — including
+// resolution done independently of, and possibly later than, isAllowedURL's
+// own lookup — so it sees the real connecting IP and closes the DNS-rebinding
+// TOCTOU window described on Webhook.
+//
+// allowPrivate disables the check entirely; it exists so tests can dial
+// httptest servers, which listen on loopback.
+func dialControl(allowPrivate bool) func(network, address string, c syscall.RawConn) error {
+	return func(network, address string, c syscall.RawConn) error {
+		if allowPrivate {
+			return nil
+		}
+		host, _, err := net.SplitHostPort(address)
+		if err != nil {
+			return errors.New("webhook: destination not allowed")
+		}
+		ip := net.ParseIP(host)
+		if ip == nil {
+			return errors.New("webhook: destination not allowed")
+		}
+		if isBlockedIP(ip) {
+			return errors.New("webhook: destination not allowed")
+		}
+		return nil
+	}
+}
+
+// newWebhookTransport builds an http.Transport whose dialer enforces the
+// SSRF guard on the actual address being connected to, for every connection
+// it opens (see dialControl). This is the guard of record; isAllowedURL is
+// only a fast pre-request rejection layered in front of it.
+func newWebhookTransport(allowPrivate bool) *http.Transport {
+	dialer := &net.Dialer{
+		Timeout:   30 * time.Second,
+		KeepAlive: 30 * time.Second,
+		Control:   dialControl(allowPrivate),
+	}
+	t := http.DefaultTransport.(*http.Transport).Clone()
+	t.DialContext = dialer.DialContext
+	return t
+}
+
 func (w *Webhook) Send(ctx context.Context, cfg json.RawMessage, secret string, ev Event) error {
 	var c struct {
 		URL string `json:"url"`