fix(backend): block SSRF via webhook subscription URLs

WebhooksService.create() rejected obviously private, loopback, or
link-local URLs (incl. cloud metadata 169.254.169.254 and the
decimal/octal/hex IPv4 shorthand encodings the WHATWG URL parser
normalizes) so an admin-configured webhook can no longer be used to
proxy requests into internal infrastructure. Registration-time only,
no DNS resolution (DNS-rebinding is out of scope for this check).

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

@@ -0,0 +1,73 @@
+import { BadRequestException } from '@nestjs/common';
+import { assertPublicWebhookUrl } from './webhook-url-guard';
+
+describe('assertPublicWebhookUrl', () => {
+  it('accepts a normal public https URL', () => {
+    expect(() =>
+      assertPublicWebhookUrl('https://example.com/hook'),
+    ).not.toThrow();
+  });
+
+  it('rejects an invalid URL', () => {
+    expect(() => assertPublicWebhookUrl('not-a-url')).toThrow(
+      BadRequestException,
+    );
+  });
+
+  it('rejects non-http(s) schemes', () => {
+    expect(() => assertPublicWebhookUrl('ftp://example.com/hook')).toThrow(
+      BadRequestException,
+    );
+    expect(() => assertPublicWebhookUrl('file:///etc/passwd')).toThrow(
+      BadRequestException,
+    );
+  });
+
+  it('rejects localhost by hostname', () => {
+    expect(() => assertPublicWebhookUrl('http://localhost/hook')).toThrow(
+      BadRequestException,
+    );
+  });
+
+  it('rejects IPv4 loopback and its shorthand/decimal/hex/octal encodings', () => {
+    for (const url of [
+      'http://127.0.0.1/hook',
+      'http://127.1/hook',
+      'http://0x7f000001/hook',
+      'http://2130706433/hook',
+      'http://017700000001/hook',
+    ]) {
+      expect(() => assertPublicWebhookUrl(url)).toThrow(BadRequestException);
+    }
+  });
+
+  it('rejects RFC 1918 private ranges', () => {
+    for (const url of [
+      'http://10.0.0.5/hook',
+      'http://172.16.0.5/hook',
+      'http://172.31.255.255/hook',
+      'http://192.168.1.1/hook',
+    ]) {
+      expect(() => assertPublicWebhookUrl(url)).toThrow(BadRequestException);
+    }
+  });
+
+  it('rejects link-local addresses including the cloud metadata endpoint', () => {
+    expect(() =>
+      assertPublicWebhookUrl('http://169.254.169.254/latest/meta-data/'),
+    ).toThrow(BadRequestException);
+  });
+
+  it('does not reject a public IPv4 literal outside reserved ranges', () => {
+    expect(() => assertPublicWebhookUrl('http://8.8.8.8/hook')).not.toThrow();
+  });
+
+  it('rejects IPv6 loopback and link-local addresses', () => {
+    expect(() => assertPublicWebhookUrl('http://[::1]/hook')).toThrow(
+      BadRequestException,
+    );
+    expect(() => assertPublicWebhookUrl('http://[fe80::1]/hook')).toThrow(
+      BadRequestException,
+    );
+  });
+});

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

@@ -0,0 +1,66 @@
+import { BadRequestException } from '@nestjs/common';
+import * as net from 'node:net';
+
+const BLOCKED_HOSTNAMES = new Set(['localhost', '0.0.0.0']);
+
+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"
+  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;
+}
+
+/**
+ * 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.
+ */
+export function assertPublicWebhookUrl(rawUrl: string): void {
+  let parsed: URL;
+  try {
+    parsed = new URL(rawUrl);
+  } catch {
+    throw new BadRequestException('Invalid webhook URL');
+  }
+
+  if (parsed.protocol !== 'http:' && parsed.protocol !== 'https:') {
+    throw new BadRequestException('Webhook URL must use http or https');
+  }
+
+  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',
+    );
+  }
+  if (net.isIP(hostname) && isPrivateOrReservedIp(hostname)) {
+    throw new BadRequestException(
+      'Webhook URL must not target a private, loopback, or link-local address',
+    );
+  }
+}

ApiCore-Backend/src/webhooks/webhooks.service.ts

@@ -5,6 +5,7 @@ import { AuditLogService } from '../audit/audit-log.service';
 import { WebhookSubscription } from '../../generated/prisma';
 import { CreateWebhookDto } from './dto/create-webhook.dto';
 import { WebhookEvent } from './webhook-events';
+import { assertPublicWebhookUrl } from './webhook-url-guard';
 
 const SECRET_BYTES = 32;
 
@@ -36,6 +37,7 @@ export class WebhooksService {
     dto: CreateWebhookDto,
     actingUserId: string,
   ): Promise<WebhookSubscription> {
+    assertPublicWebhookUrl(dto.url);
     const secret = crypto.randomBytes(SECRET_BYTES).toString('hex');
     const subscription = await this.prisma.webhookSubscription.create({
       data: {