From 5437285451c6639c8d35f4977e59d4de04227d6e Mon Sep 17 00:00:00 2001
From: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
Date: Tue, 19 May 2026 08:45:41 +0000
Subject: [PATCH] fix(mcp): drop orphan user-field keys + reject duplicate
 field_keys

---
 litellm/proxy/_types.py                       | 28 +++++++++++++++++++
 .../mcp_management_endpoints.py               |  3 +-
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/litellm/proxy/_types.py b/litellm/proxy/_types.py
index c89e6ef0f35..a2b41095af0 100644
--- a/litellm/proxy/_types.py
+++ b/litellm/proxy/_types.py
@@ -1268,6 +1268,24 @@ class MCPUserField(LiteLLMPydanticObjectBase):
     env_var_name: Optional[str] = None
 
 
+def _validate_unique_user_field_keys(
+    user_fields: List[MCPUserField],
+) -> List[MCPUserField]:
+    seen: set = set()
+    duplicates: set = set()
+    for entry in user_fields:
+        key = entry.field_key
+        if key in seen:
+            duplicates.add(key)
+        else:
+            seen.add(key)
+    if duplicates:
+        raise ValueError(
+            f"user_fields contains duplicate field_key values: {sorted(duplicates)}"
+        )
+    return user_fields
+
+
 class MCPUserFieldValuesRequest(LiteLLMPydanticObjectBase):
     """Body for storing the calling user's values for an MCP server's user fields."""
 
@@ -1368,6 +1386,11 @@ class NewMCPServerRequest(LiteLLMPydanticObjectBase):
         """
         return values
 
+    @field_validator("user_fields")
+    @classmethod
+    def _user_fields_unique(cls, v: List[MCPUserField]) -> List[MCPUserField]:
+        return _validate_unique_user_field_keys(v)
+
 
 class UpdateMCPServerRequest(LiteLLMPydanticObjectBase):
     server_id: str
@@ -1427,6 +1450,11 @@ class UpdateMCPServerRequest(LiteLLMPydanticObjectBase):
                     )
         return values
 
+    @field_validator("user_fields")
+    @classmethod
+    def _user_fields_unique(cls, v: List[MCPUserField]) -> List[MCPUserField]:
+        return _validate_unique_user_field_keys(v)
+
 
 class LiteLLM_MCPServerTable(LiteLLMPydanticObjectBase):
     """Represents a LiteLLM_MCPServerTable record"""
diff --git a/litellm/proxy/management_endpoints/mcp_management_endpoints.py b/litellm/proxy/management_endpoints/mcp_management_endpoints.py
index c6f7e65ebd6..010816db042 100644
--- a/litellm/proxy/management_endpoints/mcp_management_endpoints.py
+++ b/litellm/proxy/management_endpoints/mcp_management_endpoints.py
@@ -2166,8 +2166,9 @@ if MCP_AVAILABLE:
                 user_fields.append(MCPUserField(**entry))
             except Exception:  # noqa: BLE001 — drop malformed entries silently
                 continue
+        declared_keys = {f.field_key for f in user_fields}
         stored: Dict[str, str] = stored_values or {}
-        stored_keys = [k for k, v in stored.items() if v]
+        stored_keys = [k for k, v in stored.items() if v and k in declared_keys]
         missing_keys = [
             f.field_key
             for f in user_fields