From e73114af2f2bf05213436f8e97f0200aee648c11 Mon Sep 17 00:00:00 2001
From: Mrunmayee Daware <165297479+Mrun25@users.noreply.github.com>
Date: Fri, 9 Oct 2026 17:27:55 +0000
Subject: [PATCH] fix(proxy): enforce the key's own max_budget in common_checks
 for custom-auth requests

---
 litellm/proxy/auth/auth_checks.py             |  11 ++
 .../auth/test_key_max_budget_common_checks.py | 112 ++++++++++++++++++
 2 files changed, 123 insertions(+)
 create mode 100644 tests/unit/proxy/auth/test_key_max_budget_common_checks.py

diff --git a/litellm/proxy/auth/auth_checks.py b/litellm/proxy/auth/auth_checks.py
index 1435033e1be..5c1959bcc6e 100644
--- a/litellm/proxy/auth/auth_checks.py
+++ b/litellm/proxy/auth/auth_checks.py
@@ -1273,6 +1273,17 @@ async def common_checks(
                 ),
                 _team_multi_budget_check(team_object=team_object),
                 _virtual_key_multi_budget_check(valid_token=valid_token) if valid_token is not None else None,
+                # The key's own max_budget. The stock virtual-key branch runs
+                # this inline, but custom-auth requests (custom_auth_run_common_checks)
+                # only pass through this gather, so without it a key's max_budget
+                # is never enforced on that path.
+                virtual_key_max_budget_check(
+                    valid_token=valid_token,
+                    proxy_logging_obj=proxy_logging_obj,
+                    user_obj=user_object,
+                )
+                if valid_token is not None and RouteChecks.is_llm_api_route(route=route)
+                else None,
                 _team_soft_budget_check(
                     team_object=team_object,
                     proxy_logging_obj=proxy_logging_obj,
diff --git a/tests/unit/proxy/auth/test_key_max_budget_common_checks.py b/tests/unit/proxy/auth/test_key_max_budget_common_checks.py
new file mode 100644
index 00000000000..21e791e437b
--- /dev/null
+++ b/tests/unit/proxy/auth/test_key_max_budget_common_checks.py
@@ -0,0 +1,112 @@
+"""
+Regression tests for #45605: key max_budget enforcement in common_checks.
+
+With custom_auth_run_common_checks enabled, custom-auth requests only pass
+through common_checks() - the stock virtual-key branch that calls
+virtual_key_max_budget_check is never reached. common_checks must therefore
+enforce the key's own max_budget itself, or a budgeted key overspends.
+"""
+
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+import litellm
+from litellm.proxy._types import UserAPIKeyAuth
+from litellm.proxy.auth.auth_checks import common_checks
+from litellm.proxy.utils import ProxyLogging
+
+
+def _make_common_checks_kwargs(valid_token: UserAPIKeyAuth, route: str) -> dict:
+    mock_request = MagicMock()
+    mock_request.url.path = route
+
+    mock_proxy_logging = MagicMock(spec=ProxyLogging)
+    mock_proxy_logging.budget_alerts = AsyncMock()
+
+    return {
+        "request_body": {"model": "gpt-4"},
+        "team_object": None,
+        "user_object": None,
+        "end_user_object": None,
+        "global_proxy_spend": None,
+        "general_settings": {},
+        "route": route,
+        "llm_router": None,
+        "proxy_logging_obj": mock_proxy_logging,
+        "valid_token": valid_token,
+        "request": mock_request,
+    }
+
+
+@pytest.mark.asyncio
+async def test_key_max_budget_enforced_in_common_checks():
+    """
+    A key over its own max_budget must be rejected by common_checks on LLM
+    routes. On unfixed main this raises nothing - the check only ran in the
+    stock virtual-key branch of user_api_key_auth_builder.
+    """
+    valid_token = UserAPIKeyAuth(
+        token="sk-test-key-over-budget",
+        max_budget=100.0,
+        spend=150.0,
+    )
+
+    with (
+        patch("litellm.proxy.proxy_server.prisma_client"),
+        patch("litellm.proxy.proxy_server.user_api_key_cache"),
+        patch("litellm.proxy.proxy_server.get_current_spend", new_callable=AsyncMock) as mock_spend,
+    ):
+        mock_spend.return_value = 150.0
+
+        with pytest.raises(litellm.BudgetExceededError) as exc_info:
+            await common_checks(**_make_common_checks_kwargs(valid_token=valid_token, route="/v1/chat/completions"))
+
+        assert exc_info.value.max_budget == 100.0
+        assert exc_info.value.current_cost == 150.0
+
+
+@pytest.mark.asyncio
+async def test_key_under_max_budget_passes_common_checks():
+    """A key under its max_budget sails through."""
+    valid_token = UserAPIKeyAuth(
+        token="sk-test-key-under-budget",
+        max_budget=100.0,
+        spend=10.0,
+    )
+
+    with (
+        patch("litellm.proxy.proxy_server.prisma_client"),
+        patch("litellm.proxy.proxy_server.user_api_key_cache"),
+        patch("litellm.proxy.proxy_server.get_current_spend", new_callable=AsyncMock) as mock_spend,
+    ):
+        mock_spend.return_value = 10.0
+
+        result = await common_checks(
+            **_make_common_checks_kwargs(valid_token=valid_token, route="/v1/chat/completions")
+        )
+        assert result is True
+
+
+@pytest.mark.asyncio
+async def test_key_max_budget_not_enforced_on_non_llm_routes():
+    """
+    Parity with the stock branch: the key max_budget check is gated on LLM
+    API routes, so key-management routes stay reachable even over budget.
+    """
+    valid_token = UserAPIKeyAuth(
+        token="sk-test-key-admin-route",
+        max_budget=100.0,
+        spend=150.0,
+    )
+
+    with (
+        patch("litellm.proxy.proxy_server.prisma_client"),
+        patch("litellm.proxy.proxy_server.user_api_key_cache"),
+        patch("litellm.proxy.proxy_server.get_current_spend", new_callable=AsyncMock) as mock_spend,
+    ):
+        mock_spend.return_value = 150.0
+
+        result = await common_checks(**_make_common_checks_kwargs(valid_token=valid_token, route="/key/info"))
+        assert result is True
+        mock_spend.assert_not_called()