fix(pwa): reject malformed password hashes

apps/pwa/src/lib/crypto.mjs

@@ -11,9 +11,14 @@ export function hashPassword(password) {
 
 export function verifyPassword(password, stored) {
   if (!stored || !stored.startsWith("scrypt$")) return false;
-  const [, saltHex, hashHex] = stored.split("$");
+  const parts = stored.split("$");
+  if (parts.length !== 3) return false;
+  const [, saltHex, hashHex] = parts;
+  if (!/^[0-9a-f]+$/i.test(saltHex) || !/^[0-9a-f]+$/i.test(hashHex)) return false;
+  if (saltHex.length % 2 !== 0 || hashHex.length % 2 !== 0) return false;
   const salt = Buffer.from(saltHex, "hex");
   const expected = Buffer.from(hashHex, "hex");
+  if (salt.length === 0 || expected.length === 0) return false;
   const dk = crypto.scryptSync(String(password), salt, expected.length);
   return dk.length === expected.length && crypto.timingSafeEqual(dk, expected);
 }

apps/pwa/test/password-hash.test.mjs

@@ -0,0 +1,22 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { hashPassword, verifyPassword } from "../src/lib/crypto.mjs";
+
+test("verifyPassword accepts a matching scrypt password hash", () => {
+  const stored = hashPassword("correct horse");
+
+  assert.equal(verifyPassword("correct horse", stored), true);
+  assert.equal(verifyPassword("wrong horse", stored), false);
+});
+
+test("verifyPassword rejects malformed scrypt hashes", () => {
+  for (const stored of [
+    "scrypt$00$",
+    "scrypt$00$nothex",
+    "scrypt$zz$aa",
+    "scrypt$0$aa",
+    "scrypt$00$aa$extra",
+  ]) {
+    assert.equal(verifyPassword("anything", stored), false, stored);
+  }
+});