fix: secure twilio webhook verification

CHANGELOG.md

@@ -38,6 +38,7 @@ Status: unreleased.
 
 ### Fixes
 - Telegram: wrap reasoning italics per line to avoid raw underscores. (#2181) Thanks @YuriNachos.
+- Voice Call: enforce Twilio webhook signature verification for ngrok URLs; disable ngrok free tier bypass by default.
 - Security: harden Tailscale Serve auth by validating identity via local tailscaled before trusting headers.
 - Build: align memory-core peer dependency with lockfile.
 - Security: add mDNS discovery mode with minimal default to reduce information disclosure. (#1882) Thanks @orlyjamie.

docs/plugins/voice-call.md

@@ -103,6 +103,8 @@ Notes:
 - Plivo requires a **publicly reachable** webhook URL.
 - `mock` is a local dev provider (no network calls).
 - `skipSignatureVerification` is for local testing only.
+- If you use ngrok free tier, set `publicUrl` to the exact ngrok URL; signature verification is always enforced.
+- Ngrok free tier URLs can change or add interstitial behavior; if `publicUrl` drifts, Twilio signatures will fail. For production, prefer a stable domain or Tailscale funnel.
 
 ## TTS for calls
 

extensions/voice-call/src/config.test.ts

@@ -19,7 +19,7 @@ function createBaseConfig(
     maxConcurrentCalls: 1,
     serve: { port: 3334, bind: "127.0.0.1", path: "/voice/webhook" },
     tailscale: { mode: "off", path: "/voice/webhook" },
-    tunnel: { provider: "none", allowNgrokFreeTier: true },
+    tunnel: { provider: "none", allowNgrokFreeTier: false },
     streaming: {
       enabled: false,
       sttProvider: "openai-realtime",

extensions/voice-call/src/config.ts

@@ -217,13 +217,12 @@ export const VoiceCallTunnelConfigSchema = z
     /**
      * Allow ngrok free tier compatibility mode.
      * When true, signature verification failures on ngrok-free.app URLs
-     * will be logged but allowed through. Less secure, but necessary
+     * will include extra diagnostics. Signature verification is still required.
-     * for ngrok free tier which may modify URLs.
      */
-    allowNgrokFreeTier: z.boolean().default(true),
+    allowNgrokFreeTier: z.boolean().default(false),
   })
   .strict()
-  .default({ provider: "none", allowNgrokFreeTier: true });
+  .default({ provider: "none", allowNgrokFreeTier: false });
 export type VoiceCallTunnelConfig = z.infer<typeof VoiceCallTunnelConfigSchema>;
 
 // -----------------------------------------------------------------------------
@@ -418,11 +417,14 @@ export function resolveVoiceCallConfig(config: VoiceCallConfig): VoiceCallConfig
   }
 
   // Tunnel Config
-  resolved.tunnel = resolved.tunnel ?? { provider: "none", allowNgrokFreeTier: true };
+  resolved.tunnel = resolved.tunnel ?? {
+    provider: "none",
+    allowNgrokFreeTier: false,
+  };
   resolved.tunnel.ngrokAuthToken =
-      resolved.tunnel.ngrokAuthToken ?? process.env.NGROK_AUTHTOKEN;
+    resolved.tunnel.ngrokAuthToken ?? process.env.NGROK_AUTHTOKEN;
-  resolved.tunnel.ngrokDomain = 
+  resolved.tunnel.ngrokDomain =
-      resolved.tunnel.ngrokDomain ?? process.env.NGROK_DOMAIN;
+    resolved.tunnel.ngrokDomain ?? process.env.NGROK_DOMAIN;
 
   return resolved;
 }

extensions/voice-call/src/providers/twilio/webhook.ts

@@ -11,7 +11,7 @@ export function verifyTwilioProviderWebhook(params: {
 }): WebhookVerificationResult {
   const result = verifyTwilioWebhook(params.ctx, params.authToken, {
     publicUrl: params.currentPublicUrl || undefined,
-    allowNgrokFreeTier: params.options.allowNgrokFreeTier ?? true,
+    allowNgrokFreeTier: params.options.allowNgrokFreeTier ?? false,
     skipVerification: params.options.skipVerification,
   });
 

extensions/voice-call/src/runtime.ts

@@ -48,7 +48,7 @@ function resolveProvider(config: VoiceCallConfig): VoiceCallProvider {
           authToken: config.twilio?.authToken,
         },
         {
-          allowNgrokFreeTier: config.tunnel?.allowNgrokFreeTier ?? true,
+          allowNgrokFreeTier: config.tunnel?.allowNgrokFreeTier ?? false,
           publicUrl: config.publicUrl,
           skipVerification: config.skipSignatureVerification,
           streamPath: config.streaming?.enabled

extensions/voice-call/src/webhook-security.test.ts

@@ -205,4 +205,29 @@ describe("verifyTwilioWebhook", () => {
 
     expect(result.ok).toBe(true);
   });
+
+  it("rejects invalid signatures even with ngrok free tier enabled", () => {
+    const authToken = "test-auth-token";
+    const postBody = "CallSid=CS123&CallStatus=completed&From=%2B15550000000";
+
+    const result = verifyTwilioWebhook(
+      {
+        headers: {
+          host: "127.0.0.1:3334",
+          "x-forwarded-proto": "https",
+          "x-forwarded-host": "attacker.ngrok-free.app",
+          "x-twilio-signature": "invalid",
+        },
+        rawBody: postBody,
+        url: "http://127.0.0.1:3334/voice/webhook",
+        method: "POST",
+      },
+      authToken,
+      { allowNgrokFreeTier: true },
+    );
+
+    expect(result.ok).toBe(false);
+    expect(result.isNgrokFreeTier).toBe(true);
+    expect(result.reason).toMatch(/Invalid signature/);
+  });
 });

extensions/voice-call/src/webhook-security.ts

@@ -195,18 +195,6 @@ export function verifyTwilioWebhook(
     verificationUrl.includes(".ngrok-free.app") ||
     verificationUrl.includes(".ngrok.io");
 
-  if (isNgrokFreeTier && options?.allowNgrokFreeTier) {
-    console.warn(
-      "[voice-call] Twilio signature validation failed (proceeding for ngrok free tier compatibility)",
-    );
-    return {
-      ok: true,
-      reason: "ngrok free tier compatibility mode",
-      verificationUrl,
-      isNgrokFreeTier: true,
-    };
-  }
-
   return {
     ok: false,
     reason: `Invalid signature for URL: ${verificationUrl}`,