From 53d386050b6244b4c0d8865625cca178c757400d Mon Sep 17 00:00:00 2001
From: = <=>
Date: Mon, 29 Jun 2026 11:34:24 -0700
Subject: [PATCH] fix(crypto): reject invalid hex operands in
 timingSafeEqualHex

---
 src/utils/crypto.ts      |  5 +++--
 test/unit/crypto.test.ts | 12 +++++++++++-
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/src/utils/crypto.ts b/src/utils/crypto.ts
index 2236b6ec33..aaf47fb5cc 100644
--- a/src/utils/crypto.ts
+++ b/src/utils/crypto.ts
@@ -24,6 +24,7 @@ export async function verifyGitHubSignature(rawBody: string, signatureHeader: st
 export function timingSafeEqualHex(left: string, right: string): boolean {
   const leftBytes = hexToBytes(left);
   const rightBytes = hexToBytes(right);
+  if (!leftBytes || !rightBytes) return false;
   if (leftBytes.length !== rightBytes.length) return false;
   let result = 0;
   for (let index = 0; index < leftBytes.length; index += 1) {
@@ -32,8 +33,8 @@ export function timingSafeEqualHex(left: string, right: string): boolean {
   return result === 0;
 }
 
-function hexToBytes(hex: string): Uint8Array {
-  if (!/^[0-9a-f]+$/i.test(hex) || hex.length % 2 !== 0) return new Uint8Array();
+function hexToBytes(hex: string): Uint8Array | null {
+  if (hex.length === 0 || hex.length % 2 !== 0 || !/^[0-9a-f]+$/i.test(hex)) return null;
   const bytes = new Uint8Array(hex.length / 2);
   for (let index = 0; index < bytes.length; index += 1) {
     bytes[index] = Number.parseInt(hex.slice(index * 2, index * 2 + 2), 16);
diff --git a/test/unit/crypto.test.ts b/test/unit/crypto.test.ts
index 76ea5d8129..90ef7f836a 100644
--- a/test/unit/crypto.test.ts
+++ b/test/unit/crypto.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, it } from "vitest";
 import { createOpaqueToken, hashToken, timingSafeEqual } from "../../src/auth/security";
-import { verifyGitHubSignature } from "../../src/utils/crypto";
+import { verifyGitHubSignature, timingSafeEqualHex } from "../../src/utils/crypto";
 
 describe("webhook signature verification", () => {
   it("accepts valid GitHub HMAC signatures and rejects tampering", async () => {
@@ -17,6 +17,16 @@ describe("webhook signature verification", () => {
     await expect(verifyGitHubSignature(body, null, secret)).resolves.toBe(false);
     await expect(verifyGitHubSignature(body, "bad-prefix", secret)).resolves.toBe(false);
     await expect(verifyGitHubSignature(body, `sha256=${signature}`, "")).resolves.toBe(false);
+    await expect(verifyGitHubSignature(body, "sha256=not-valid-hex", secret)).resolves.toBe(false);
+  });
+
+  it("rejects invalid hex operands in timingSafeEqualHex", () => {
+    expect(timingSafeEqualHex("zz", "yy")).toBe(false);
+    expect(timingSafeEqualHex("not-hex-a", "not-hex-b")).toBe(false);
+    expect(timingSafeEqualHex("abc", "abcd")).toBe(false);
+    expect(timingSafeEqualHex("", "00")).toBe(false);
+    expect(timingSafeEqualHex("00", "01")).toBe(false);
+    expect(timingSafeEqualHex("00", "00")).toBe(true);
   });
 
   it("uses timing-safe token comparisons and one-way token hashes", async () => {