🛡️ Sentinel: [CRITICAL] Fix timing attack vulnerability in secret comparisons#43
🛡️ Sentinel: [CRITICAL] Fix timing attack vulnerability in secret comparisons#43aloewright wants to merge 1 commit into
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…parisons Co-authored-by: aloewright <3641844+aloewright@users.noreply.github.com>
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: Organization UI Review profile: CHILL Plan: Pro Run ID: 📒 Files selected for processing (2)
WalkthroughThis PR improves timing-safe cryptographic comparisons in two security-critical paths. Webhook signature verification and admin key validation now pre-encode expected values to bytes and use ChangesSecurity improvements
Estimated code review effort🎯 2 (Simple) | ⏱️ ~12 minutes 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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| Status | Name | Latest Commit | Updated (UTC) |
|---|---|---|---|
| ✅ Deployment successful! View logs |
postpilot | 7da0f77 | May 26 2026, 05:27 AM |
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Code Review
This pull request attempts to secure timing-safe comparisons by manually encoding strings into Uint8Array buffers using TextEncoder before passing them to Hono's timingSafeEqual function. However, the feedback points out that Hono's timingSafeEqual utility already natively handles raw strings of different lengths by internally encoding and hashing them. Consequently, manually instantiating TextEncoder is redundant and adds unnecessary overhead in both polar.ts and admin.ts, and should be reverted to passing raw strings directly.
| const enc = new TextEncoder(); | ||
| const expectedBuf = enc.encode(expected); | ||
| for (const c of candidates) { | ||
| const [version, sig] = c.split(","); | ||
| if (version === "v1" && sig && (await timingSafeEqual(sig, expected))) { | ||
| if ( | ||
| version === "v1" && | ||
| sig && | ||
| (await timingSafeEqual(enc.encode(sig), expectedBuf)) | ||
| ) { | ||
| return true; | ||
| } | ||
| } |
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Hono's timingSafeEqual utility natively supports raw strings of different lengths. Internally, it automatically converts strings to Uint8Array using TextEncoder and hashes both inputs using SHA-256 before performing a constant-time comparison.
Because of this, manually instantiating TextEncoder and encoding the strings beforehand is redundant and adds unnecessary overhead. We can safely revert to passing the raw strings directly.
for (const c of candidates) {
const [version, sig] = c.split(",");
if (version === "v1" && sig && (await timingSafeEqual(sig, expected))) {
return true;
}
}| const enc = new TextEncoder(); | ||
| if (!(await timingSafeEqual(enc.encode(expected), enc.encode(provided)))) { | ||
| throw new HTTPException(401, { message: "Invalid admin key." }); | ||
| } |
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As with the webhook verification, Hono's timingSafeEqual natively handles raw strings by encoding and hashing them internally. Manually encoding expected and provided with TextEncoder is redundant. We can simplify this check by passing the strings directly.
if (!(await timingSafeEqual(expected, provided))) {
throw new HTTPException(401, { message: "Invalid admin key." });
}There was a problem hiding this comment.
Pull request overview
This PR hardens secret comparisons against timing attacks by ensuring inputs to Hono’s timingSafeEqual are compared as byte arrays rather than raw strings, affecting both the admin key middleware and Polar webhook signature verification.
Changes:
- Encode admin key strings with
TextEncoderbefore constant-time comparison. - Encode Polar webhook signatures/expected values as
Uint8Arraybefore constant-time comparison (and avoid re-encoding the expected value inside the loop).
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| apps/quill/src/routes/admin.ts | Encodes admin key strings to bytes before timingSafeEqual check. |
| apps/quill/src/lib/polar.ts | Encodes webhook signature strings to bytes for constant-time comparison; pre-encodes expected signature bytes once per request. |
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| const enc = new TextEncoder(); | ||
| if (!(await timingSafeEqual(enc.encode(expected), enc.encode(provided)))) { |
| const enc = new TextEncoder(); | ||
| const expectedBuf = enc.encode(expected); |
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🚨 Severity: CRITICAL
💡 Vulnerability: Passing raw strings to
timingSafeEqualdoes not prevent timing attacks, and custom constant-time implementations suffer from JS optimization. Hono'stimingSafeEqualimplementation may degrade to standard JS checks or be incompatible with raw strings.🎯 Impact: Attackers could measure the time taken to reject an invalid admin key or webhook signature, eventually brute-forcing the key or signature byte-by-byte via timing side-channel attacks.
🔧 Fix: Updated the calls in
admin.tsandpolar.tsto convert strings toUint8Arrays usingTextEncoderbefore passing them to the asynchronoustimingSafeEqual. This ensures proper constant-time array/buffer comparison.✅ Verification: Tested via local development checking scripts (
pnpm check,pnpm typecheck,pnpm test), confirming no functional or compilation regressions while improving underlying runtime execution paths.PR created automatically by Jules for task 5850615133187745739 started by @aloewright
Summary by CodeRabbit