From 78fca260604778e1aed6474c52b39f8982e2c7cd Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Wed, 22 Jul 2026 21:06:53 +0000
Subject: [PATCH] Fix timing attack vulnerability in token validation

---
 .jules/sentinel.md        | 4 ++++
 src/cli/commands/serve.ts | 9 +++------
 2 files changed, 7 insertions(+), 6 deletions(-)
 create mode 100644 .jules/sentinel.md

diff --git a/.jules/sentinel.md b/.jules/sentinel.md
new file mode 100644
index 00000000..445506d4
--- /dev/null
+++ b/.jules/sentinel.md
@@ -0,0 +1,4 @@
+## 2026-07-22 - Fix Timing Attack Vulnerability in Token Comparison
+**Vulnerability:** Checking buffer lengths before calling `crypto.timingSafeEqual` creates a short-circuit fast path that leaks the secret's length via timing differences.
+**Learning:** `crypto.timingSafeEqual` throws an error if buffers have different lengths, so checking lengths first seems necessary, but it introduces a timing attack vulnerability.
+**Prevention:** Always hash both secrets to a fixed length (e.g., using `crypto.createHash('sha256')`) before comparison to ensure true constant-time evaluation.
diff --git a/src/cli/commands/serve.ts b/src/cli/commands/serve.ts
index 2c37293e..505ac4bd 100644
--- a/src/cli/commands/serve.ts
+++ b/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 expectedHash = crypto.createHash('sha256').update(authToken).digest();
+              if (crypto.timingSafeEqual(tokenHash, expectedHash)) {
                 isAuthenticated = true;
                 break;
               }