fix(proxy): reject non-finite spend via validate_finite_spend

A NaN/-inf spend would bypass spend >= max_budget enforcement. Add a
shared finite-value guard, defined above the litellm.proxy.* imports to
avoid the module-level cyclic-import warning.

litellm/proxy/management_endpoints/common_utils.py

@@ -1,8 +1,27 @@
+import math
 from typing import TYPE_CHECKING, Any, Dict, Optional, Union
 
 from fastapi import HTTPException, status
 from pydantic import BaseModel
 
+
+# Defined above the `litellm.proxy.*` imports so the name is bound even when
+# this module is imported first through the proxy import cycle (CodeQL:
+# module-level cyclic import). Depends only on `math` + `HTTPException`.
+def validate_finite_spend(spend: Optional[float]) -> None:
+    """Reject NaN/±inf spend before it reaches the DB / spend counter.
+
+    A non-finite spend would otherwise slip past `spend >= max_budget`
+    enforcement, since any comparison with NaN (and `-inf >= max_budget`)
+    is False, letting the entity keep spending past its configured budget.
+    """
+    if spend is not None and not math.isfinite(spend):
+        raise HTTPException(
+            status_code=400,
+            detail={"error": f"spend must be a finite number. Received: {spend}"},
+        )
+
+
 from litellm._logging import verbose_proxy_logger
 from litellm.caching import DualCache
 from litellm.proxy._types import (

tests/test_litellm/proxy/management_endpoints/test_common_utils.py

@@ -570,3 +570,35 @@ class TestRequireCallerUserIdForNonAdmin:
 
         assert exc_info.value.status_code == 403
         assert "Service-account keys" in str(exc_info.value.detail)
+
+
+class TestValidateFiniteSpend:
+    """`validate_finite_spend` rejects NaN/±inf so a non-finite spend cannot
+    bypass `spend >= max_budget` enforcement (NaN/-inf compare false)."""
+
+    def test_none_is_allowed(self):
+        from litellm.proxy.management_endpoints.common_utils import (
+            validate_finite_spend,
+        )
+
+        assert validate_finite_spend(None) is None
+
+    def test_finite_value_is_allowed(self):
+        from litellm.proxy.management_endpoints.common_utils import (
+            validate_finite_spend,
+        )
+
+        assert validate_finite_spend(0.0) is None
+        assert validate_finite_spend(12.5) is None
+
+    @pytest.mark.parametrize("bad", [float("nan"), float("inf"), float("-inf")])
+    def test_non_finite_is_rejected(self, bad):
+        from fastapi import HTTPException
+
+        from litellm.proxy.management_endpoints.common_utils import (
+            validate_finite_spend,
+        )
+
+        with pytest.raises(HTTPException) as exc_info:
+            validate_finite_spend(bad)
+        assert exc_info.value.status_code == 400