fix: block telemetry endpoint from pointing at internal hosts

app/api/admin/telemetry/route.ts

@@ -11,6 +11,7 @@ import {
   reschedule,
   DEFAULT_ENDPOINT,
   getLoginCounts,
+  resolveEndpointAllowed,
 } from '@/lib/telemetry';
 
 /**
@@ -100,8 +101,11 @@ export async function POST(request: NextRequest) {
         return NextResponse.json({ error: 'endpoint required' }, { status: 400 });
       }
       const trimmed = body.endpoint.trim();
-      if (trimmed && !/^https?:\/\//i.test(trimmed)) {
+      if (trimmed) {
-        return NextResponse.json({ error: 'endpoint must be http(s)://' }, { status: 400 });
+        const check = await resolveEndpointAllowed(trimmed);
+        if (!check.ok) {
+          return NextResponse.json({ error: check.reason }, { status: 400 });
+        }
       }
       const state = await loadState();
       const before = state.endpoint;

lib/telemetry/endpoint-guard.ts

@@ -0,0 +1,115 @@
+import { lookup } from 'node:dns/promises';
+import { isIP } from 'node:net';
+
+// Block telemetry endpoints from pointing at internal/loopback addresses.
+// Required because the admin UI lets an authenticated admin set an arbitrary
+// URL; without this an attacker with a session (or a hostile admin in a
+// multi-tenant deploy) could redirect heartbeats at internal hosts.
+//
+// Set BULWARK_TELEMETRY_ALLOW_PRIVATE=1 to bypass — useful only for local
+// dev where the collector is on the loopback.
+
+const PRIVATE_V4: RegExp[] = [
+  /^0\./,                                          // 0.0.0.0/8
+  /^10\./,                                         // 10.0.0.0/8
+  /^127\./,                                        // loopback
+  /^169\.254\./,                                   // link-local + cloud metadata
+  /^172\.(1[6-9]|2\d|3[0-1])\./,                   // 172.16.0.0/12
+  /^192\.168\./,                                   // 192.168.0.0/16
+  /^192\.0\.0\./,                                  // IETF reserved
+  /^198\.(1[8-9])\./,                              // benchmarking 198.18.0.0/15
+  /^100\.(6[4-9]|[7-9]\d|1[01]\d|12[0-7])\./,      // 100.64.0.0/10 CGNAT
+  /^22[4-9]\./,                                    // 224.0.0.0/4 multicast
+  /^23\d\./,
+  /^2[4-5]\d\./,                                   // 240.0.0.0/4 reserved
+];
+
+function isPrivateV4(ip: string): boolean {
+  return PRIVATE_V4.some((re) => re.test(ip));
+}
+
+function isPrivateV6(ip: string): boolean {
+  const lower = ip.toLowerCase();
+  if (lower === '::1' || lower === '::') return true;
+  if (/^fe[89ab][0-9a-f]:/.test(lower)) return true;     // fe80::/10 link-local
+  if (/^f[cd][0-9a-f]{2}:/.test(lower)) return true;     // fc00::/7 ULA
+  const mapped = lower.match(/^::ffff:(\d+\.\d+\.\d+\.\d+)$/);
+  if (mapped) return isPrivateV4(mapped[1]);
+  return false;
+}
+
+export function isPrivateAddress(ip: string): boolean {
+  const family = isIP(ip);
+  if (family === 4) return isPrivateV4(ip);
+  if (family === 6) return isPrivateV6(ip);
+  return false;
+}
+
+const BAD_HOSTS = new Set([
+  'localhost',
+  'localhost.localdomain',
+  'ip6-localhost',
+  'ip6-loopback',
+]);
+
+function bypassEnabled(): boolean {
+  return process.env.BULWARK_TELEMETRY_ALLOW_PRIVATE === '1';
+}
+
+export type EndpointCheck = { ok: true } | { ok: false; reason: string };
+
+// Sync URL/host shape check. Catches the obvious cases without DNS.
+export function validateEndpointUrl(raw: string): EndpointCheck {
+  let url: URL;
+  try {
+    url = new URL(raw);
+  } catch {
+    return { ok: false, reason: 'invalid URL' };
+  }
+  if (url.protocol !== 'http:' && url.protocol !== 'https:') {
+    return { ok: false, reason: 'must be http(s)://' };
+  }
+  if (bypassEnabled()) return { ok: true };
+
+  const host = url.hostname.toLowerCase().replace(/^\[|\]$/g, '');
+  if (!host) return { ok: false, reason: 'host required' };
+  if (BAD_HOSTS.has(host)) {
+    return { ok: false, reason: 'localhost endpoints are not allowed' };
+  }
+  if (host.endsWith('.local') || host.endsWith('.internal') || host.endsWith('.localhost')) {
+    return { ok: false, reason: 'private TLDs are not allowed' };
+  }
+  if (isIP(host) && isPrivateAddress(host)) {
+    return { ok: false, reason: 'private/loopback IP is not allowed' };
+  }
+  return { ok: true };
+}
+
+// Async check that additionally resolves DNS hostnames. Use this on
+// set-endpoint AND immediately before fetch to defeat DNS-rebinding tricks
+// where a hostname resolves to a public IP at validation time and a private
+// one at fetch time.
+export async function resolveEndpointAllowed(raw: string): Promise<EndpointCheck> {
+  const initial = validateEndpointUrl(raw);
+  if (!initial.ok) return initial;
+  if (bypassEnabled()) return { ok: true };
+
+  const host = new URL(raw).hostname.toLowerCase().replace(/^\[|\]$/g, '');
+  if (isIP(host)) return { ok: true };
+
+  try {
+    const addrs = await lookup(host, { all: true });
+    for (const a of addrs) {
+      if (isPrivateAddress(a.address)) {
+        return { ok: false, reason: `host ${host} resolves to private address ${a.address}` };
+      }
+    }
+    return { ok: true };
+  } catch {
+    // Don't block on transient DNS failures — fetch will fail loudly anyway,
+    // and we don't want to lock admins out of their config when the resolver
+    // is flaky. The literal-IP check above already covers the direct-attack
+    // case.
+    return { ok: true };
+  }
+}

lib/telemetry/index.ts

@@ -4,6 +4,10 @@ export {
   loadState, saveState, getInstanceId, effectiveConsent,
 } from './state';
 export { recordLogin, getLoginCounts } from './login-tracker';
+export {
+  validateEndpointUrl, resolveEndpointAllowed, isPrivateAddress,
+} from './endpoint-guard';
+export type { EndpointCheck } from './endpoint-guard';
 export type {
   TelemetryPayload, TelemetryStateFile, ConsentState,
   Platform, OsFamily, CountBucket, TelemetryFeatures,

lib/telemetry/sender.ts

@@ -1,6 +1,7 @@
 import { logger } from '@/lib/logger';
 import { effectiveConsent, endpointEnabled, loadState, saveState } from './state';
 import { buildPayload } from './payload';
+import { resolveEndpointAllowed } from './endpoint-guard';
 import { DEFAULT_ENDPOINT } from './types';
 
 const DAY_MS = 24 * 60 * 60 * 1000;
@@ -24,6 +25,14 @@ export async function sendOnce(opts?: { reason?: string }): Promise<{
   const endpoint = state.endpoint || DEFAULT_ENDPOINT;
   if (!endpointEnabled(endpoint)) return { ok: false, error: 'endpoint blank' };
 
+  // Re-check at fetch time: defeats DNS rebinding, and catches the case
+  // where state.json was edited out-of-band to bypass the admin API.
+  const guard = await resolveEndpointAllowed(endpoint);
+  if (!guard.ok) {
+    logger.warn('telemetry: endpoint blocked', { reason: guard.reason });
+    return { ok: false, error: `endpoint blocked: ${guard.reason}` };
+  }
+
   const payload = await buildPayload();
   try {
     const res = await fetch(endpoint, {