diff --git a/supernote/server/services/user.py b/supernote/server/services/user.py
index 34056af9..849e4035 100644
--- a/supernote/server/services/user.py
+++ b/supernote/server/services/user.py
@@ -219,20 +219,51 @@ async def verify_login_hash(
     ) -> bool:
         user = await self._get_user_do(account)
         if not user or not user.is_active:
+            logger.warning("verify_login_hash: user %s not found or inactive", account)
             return False
 
         stored_value = await self._coordination_service.get_value(
             f"challenge:{account}"
         )
         if not stored_value:
+            logger.warning(
+                "verify_login_hash: no challenge found for %s (expired or never issued)",
+                account,
+            )
             return False
 
         random_code, stored_timestamp = stored_value.split("|")
-        if stored_timestamp != timestamp:
+        # Accept timestamps within the challenge TTL to tolerate device clock skew.
+        # Exact equality breaks when the device sends its own local time rather than
+        # echoing the server's challenge timestamp. The random_code nonce + TTL already
+        # provides replay protection, so strict equality is not needed here.
+        try:
+            ts_diff = abs(int(stored_timestamp) - int(timestamp))
+            if ts_diff > int(RANDOM_CODE_TTL.total_seconds() * 1000):
+                logger.warning(
+                    "verify_login_hash: timestamp skew too large for %s "
+                    "(stored=%s client=%s diff=%dms limit=%dms)",
+                    account,
+                    stored_timestamp,
+                    timestamp,
+                    ts_diff,
+                    int(RANDOM_CODE_TTL.total_seconds() * 1000),
+                )
+                return False
+        except ValueError:
+            logger.warning(
+                "verify_login_hash: non-numeric timestamp for %s (stored=%s client=%s)",
+                account,
+                stored_timestamp,
+                timestamp,
+            )
             return False
 
         expected_hash = hash_with_salt(user.password_md5, random_code)
-        return expected_hash == client_hash
+        if expected_hash != client_hash:
+            logger.warning("verify_login_hash: hash mismatch for %s", account)
+            return False
+        return True
 
     async def login(
         self,
diff --git a/tests/server/services/test_verify_login_hash.py b/tests/server/services/test_verify_login_hash.py
new file mode 100644
index 00000000..72a58b90
--- /dev/null
+++ b/tests/server/services/test_verify_login_hash.py
@@ -0,0 +1,80 @@
+import hashlib
+
+import pytest
+
+from supernote.models.user import UserRegisterDTO
+from supernote.server.services.user import RANDOM_CODE_TTL, UserService
+from supernote.server.utils.hashing import hash_with_salt
+
+
+@pytest.fixture
+async def registered_user(user_service: UserService) -> str:
+    email = "hashtest@example.com"
+    pw_md5 = hashlib.md5(b"password").hexdigest()
+    await user_service.register(UserRegisterDTO(email=email, password=pw_md5))
+    return email
+
+
+async def test_verify_login_hash_exact_timestamp(
+    registered_user: str, user_service: UserService
+) -> None:
+    code, ts = await user_service.generate_random_code(registered_user)
+    pw_md5 = hashlib.md5(b"password").hexdigest()
+    client_hash = hash_with_salt(pw_md5, code)
+    assert await user_service.verify_login_hash(registered_user, client_hash, ts)
+
+
+async def test_verify_login_hash_small_clock_skew(
+    registered_user: str, user_service: UserService
+) -> None:
+    code, ts = await user_service.generate_random_code(registered_user)
+    pw_md5 = hashlib.md5(b"password").hexdigest()
+    client_hash = hash_with_salt(pw_md5, code)
+    # Simulate device clock 30 seconds ahead of server
+    skewed_ts = str(int(ts) + 30_000)
+    assert await user_service.verify_login_hash(registered_user, client_hash, skewed_ts)
+
+
+async def test_verify_login_hash_skew_exceeds_ttl(
+    registered_user: str, user_service: UserService
+) -> None:
+    code, ts = await user_service.generate_random_code(registered_user)
+    pw_md5 = hashlib.md5(b"password").hexdigest()
+    client_hash = hash_with_salt(pw_md5, code)
+    # Simulate device clock 1 hour ahead — exceeds the 5-minute TTL window
+    skewed_ts = str(int(ts) + int(RANDOM_CODE_TTL.total_seconds() * 1000) + 1)
+    assert not await user_service.verify_login_hash(
+        registered_user, client_hash, skewed_ts
+    )
+
+
+async def test_verify_login_hash_non_numeric_timestamp(
+    registered_user: str, user_service: UserService
+) -> None:
+    code, _ts = await user_service.generate_random_code(registered_user)
+    pw_md5 = hashlib.md5(b"password").hexdigest()
+    client_hash = hash_with_salt(pw_md5, code)
+    assert not await user_service.verify_login_hash(
+        registered_user, client_hash, "not-a-number"
+    )
+
+
+async def test_verify_login_hash_no_challenge(
+    registered_user: str, user_service: UserService
+) -> None:
+    # Never call generate_random_code — no challenge stored
+    pw_md5 = hashlib.md5(b"password").hexdigest()
+    assert not await user_service.verify_login_hash(registered_user, pw_md5, "12345678")
+
+
+async def test_verify_login_hash_wrong_hash(
+    registered_user: str, user_service: UserService
+) -> None:
+    _code, ts = await user_service.generate_random_code(registered_user)
+    assert not await user_service.verify_login_hash(registered_user, "deadbeef" * 8, ts)
+
+
+async def test_verify_login_hash_unknown_user(user_service: UserService) -> None:
+    assert not await user_service.verify_login_hash(
+        "nobody@example.com", "hash", "12345678"
+    )