fix(backend): close two SSRF bypasses in webhook URL validation

1. The URL guard only classified IP-literal hostnames; any plain domain
   name (the common case) skipped validation entirely. Hostnames are now
   resolved via DNS and every returned address is checked against the
   same private/loopback/link-local ranges (net.BlockList), so an
   attacker-controlled domain pointed at an internal IP is rejected too.
2. fetch() follows redirects by default, so a registered public URL could
   302 to an internal target at delivery time. Delivery now uses
   redirect: 'manual' so such a redirect is never followed.

ApiCore-Backend/src/webhooks/webhook-url-guard.ts

@@ -1,46 +1,56 @@
 import { BadRequestException } from '@nestjs/common';
+import * as dns from 'node:dns/promises';
 import * as net from 'node:net';
 
-const BLOCKED_HOSTNAMES = new Set(['localhost', '0.0.0.0']);
+const BLOCKED_HOSTNAMES = new Set(['localhost']);
 
-function isPrivateOrReservedIpv4(octets: number[]): boolean {
-  const [a, b] = octets;
-  if (a === 127) return true; // loopback
-  if (a === 10) return true; // private (RFC 1918)
-  if (a === 172 && b >= 16 && b <= 31) return true; // private (RFC 1918)
-  if (a === 192 && b === 168) return true; // private (RFC 1918)
-  if (a === 169 && b === 254) return true; // link-local, incl. cloud metadata (169.254.169.254)
-  if (a === 0) return true; // "this network"
+const blockedRanges = new net.BlockList();
+blockedRanges.addSubnet('10.0.0.0', 8, 'ipv4'); // RFC 1918
+blockedRanges.addSubnet('172.16.0.0', 12, 'ipv4'); // RFC 1918
+blockedRanges.addSubnet('192.168.0.0', 16, 'ipv4'); // RFC 1918
+blockedRanges.addSubnet('127.0.0.0', 8, 'ipv4'); // loopback
+blockedRanges.addSubnet('169.254.0.0', 16, 'ipv4'); // link-local, incl. cloud metadata
+blockedRanges.addSubnet('0.0.0.0', 8, 'ipv4'); // "this network"
+blockedRanges.addAddress('::1', 'ipv6'); // loopback
+blockedRanges.addAddress('::', 'ipv6'); // unspecified
+blockedRanges.addSubnet('fe80::', 10, 'ipv6'); // link-local
+blockedRanges.addSubnet('fc00::', 7, 'ipv6'); // unique local
+
+function isBlockedIp(ip: string): boolean {
+  const version = net.isIP(ip);
+  if (version === 4) return blockedRanges.check(ip, 'ipv4');
+  if (version === 6) return blockedRanges.check(ip, 'ipv6');
   return false;
 }
 
-function isPrivateOrReservedIp(ip: string): boolean {
-  if (net.isIPv4(ip)) {
-    return isPrivateOrReservedIpv4(ip.split('.').map(Number));
-  }
-  if (net.isIPv6(ip)) {
-    const normalized = ip.toLowerCase();
-    if (normalized === '::1' || normalized === '::') return true; // loopback / unspecified
-    if (normalized.startsWith('fe80:')) return true; // link-local
-    if (normalized.startsWith('fc') || normalized.startsWith('fd')) return true; // unique local
-    const mapped = /^::ffff:(\d+\.\d+\.\d+\.\d+)$/.exec(normalized);
-    if (mapped && net.isIPv4(mapped[1])) {
-      return isPrivateOrReservedIpv4(mapped[1].split('.').map(Number));
-    }
-    return false;
-  }
-  return false;
+interface LookupAddress {
+  address: string;
+  family: number;
 }
 
+type LookupFn = (hostname: string) => Promise<LookupAddress[]>;
+
+const defaultLookup: LookupFn = (hostname) =>
+  dns.lookup(hostname, { all: true });
+
 /**
  * Blocks webhook targets that would let an admin turn the backend into an
  * SSRF proxy against internal services or the cloud metadata endpoint.
- * Checks are syntactic only (no DNS lookups), relying on the WHATWG URL
- * parser to normalize decimal/octal/hex IPv4 shorthand into dotted form
- * before the range check runs; DNS-rebinding (a hostname resolving to a
- * private address only at delivery time) is not covered.
+ *
+ * IP literals (including decimal/octal/hex shorthand, which the WHATWG URL
+ * parser normalizes before this runs) are checked directly against
+ * `net.BlockList`. Plain hostnames are resolved via DNS and every returned
+ * address is checked too, so an attacker-controlled domain pointed at an
+ * internal IP is rejected rather than silently passing the literal-only
+ * check. This still does not defend against DNS rebinding (the same
+ * hostname resolving to a different, private address only later, at actual
+ * delivery time) — closing that would require re-resolving on every
+ * delivery, which the caller intentionally does not do (see deliver()).
  */
-export function assertPublicWebhookUrl(rawUrl: string): void {
+export async function assertPublicWebhookUrl(
+  rawUrl: string,
+  lookup: LookupFn = defaultLookup,
+): Promise<void> {
   let parsed: URL;
   try {
     parsed = new URL(rawUrl);
@@ -54,13 +64,30 @@ export function assertPublicWebhookUrl(rawUrl: string): void {
 
   const hostname = parsed.hostname.toLowerCase().replace(/^\[|\]$/g, '');
   if (BLOCKED_HOSTNAMES.has(hostname)) {
-    throw new BadRequestException(
-      'Webhook URL must not target localhost or a reserved address',
-    );
+    throw new BadRequestException('Webhook URL must not target localhost');
   }
-  if (net.isIP(hostname) && isPrivateOrReservedIp(hostname)) {
+
+  if (net.isIP(hostname)) {
+    if (isBlockedIp(hostname)) {
+      throw new BadRequestException(
+        'Webhook URL must not target a private, loopback, or link-local address',
+      );
+    }
+    return;
+  }
+
+  let addresses: LookupAddress[];
+  try {
+    addresses = await lookup(hostname);
+  } catch {
+    throw new BadRequestException('Webhook URL host could not be resolved');
+  }
+  if (
+    addresses.length === 0 ||
+    addresses.some((record) => isBlockedIp(record.address))
+  ) {
     throw new BadRequestException(
-      'Webhook URL must not target a private, loopback, or link-local address',
+      'Webhook URL must not resolve to a private, loopback, or link-local address',
     );
   }
 }