🛡️ Sentinel: [CRITICAL] Fix timing attack vulnerability in auth token validation

.jules/sentinel.md

@@ -0,0 +1,4 @@
+## 2024-07-25 - Timing Attack Fast Path in Token Comparison
+**Vulnerability:** The authentication validation used a short-circuit buffer length check (`tokenBuffer.length === authTokenBuffer.length`) before calling `crypto.timingSafeEqual()`.
+**Learning:** Checking the length of secrets before a constant-time comparison creates a fast path that leaks the length of the expected secret via timing differences, rendering the constant-time check partially ineffective.
+**Prevention:** Always hash both secrets to a fixed length (e.g., using `crypto.createHash('sha256')`) before comparison to ensure true constant-time evaluation and avoid short-circuiting logic based on length.

src/cli/commands/serve.ts

@@ -346,13 +346,10 @@ export async function handleServeCommand(_options: unknown, command: Command) {
 
           let isAuthenticated = false;
           if (scheme?.toLowerCase() === 'bearer' && token) {
-            const tokenBuffer = Buffer.from(token);
+            const tokenHash = crypto.createHash('sha256').update(token).digest();
             for (const authToken of authTokens) {
-              const authTokenBuffer = Buffer.from(authToken);
-              if (
-                tokenBuffer.length === authTokenBuffer.length &&
-                crypto.timingSafeEqual(tokenBuffer, authTokenBuffer)
-              ) {
+              const authTokenHash = crypto.createHash('sha256').update(authToken).digest();
+              if (crypto.timingSafeEqual(tokenHash, authTokenHash)) {
                 isAuthenticated = true;
                 break;
               }