diff --git a/litellm/proxy/management_endpoints/key_management_endpoints.py b/litellm/proxy/management_endpoints/key_management_endpoints.py
index f69d9d2f8d..32227b3dd6 100644
--- a/litellm/proxy/management_endpoints/key_management_endpoints.py
+++ b/litellm/proxy/management_endpoints/key_management_endpoints.py
@@ -1961,22 +1961,48 @@ async def _validate_update_key_data(
         user_api_key_cache=user_api_key_cache,
     )
 
-    # Admin-only: only proxy admins, team admins, or org admins can modify max_budget or spend
-    if (
-        data.max_budget is not None and data.max_budget != existing_key_row.max_budget
+    # Cross-key authorization. Previously only gated on max_budget/spend
+    # changes, which let a non-admin blanket-rewrite any OTHER field on
+    # any key (models, alias, metadata, tpm_limit, rpm_limit,
+    # allowed_routes, guardrails, blocked, duration, permissions, …) as
+    # long as they avoided budget/spend.
+    #
+    # Policy:
+    # - Key owner (same user_id): may update non-budget fields on their
+    #   own key without the admin check.
+    # - Anyone else (non-PROXY_ADMIN, not the owner): must pass
+    #   _check_key_admin_access (PROXY_ADMIN / key-owner / team-admin /
+    #   org-admin of the key).
+    # - max_budget / spend: always require the admin check, even for the
+    #   key owner (matches the existing admin-only budget semantics).
+    is_key_owner = (
+        user_api_key_dict.user_id is not None
+        and existing_key_row.user_id == user_api_key_dict.user_id
+    )
+    _is_budget_change = (
+        data.max_budget is not None
+        and data.max_budget != existing_key_row.max_budget
     ) or (
         data.spend is not None
         and data.spend != getattr(existing_key_row, "spend", None)
+    )
+    if (
+        (not _is_proxy_admin)
+        and prisma_client is not None
+        and (not is_key_owner or _is_budget_change)
     ):
-        if prisma_client is not None:
-            hashed_key = existing_key_row.token
-            await _check_key_admin_access(
-                user_api_key_dict=user_api_key_dict,
-                hashed_token=hashed_key,
-                prisma_client=prisma_client,
-                user_api_key_cache=user_api_key_cache,
-                route="/key/update (max_budget/spend)",
-            )
+        hashed_key = existing_key_row.token
+        await _check_key_admin_access(
+            user_api_key_dict=user_api_key_dict,
+            hashed_token=hashed_key,
+            prisma_client=prisma_client,
+            user_api_key_cache=user_api_key_cache,
+            route=(
+                "/key/update (max_budget/spend)"
+                if _is_budget_change
+                else "/key/update"
+            ),
+        )
 
     # Check team limits if key has a team_id (from request or existing key)
     team_obj: Optional[LiteLLM_TeamTableCachedObj] = None
diff --git a/tests/test_litellm/proxy/management_endpoints/test_key_management_endpoints.py b/tests/test_litellm/proxy/management_endpoints/test_key_management_endpoints.py
index 479defbff5..41ab60fcf6 100644
--- a/tests/test_litellm/proxy/management_endpoints/test_key_management_endpoints.py
+++ b/tests/test_litellm/proxy/management_endpoints/test_key_management_endpoints.py
@@ -8030,6 +8030,74 @@ async def test_update_key_non_budget_fields_allowed_for_internal_user(monkeypatc
     assert result is not None
 
 
+@pytest.mark.asyncio
+async def test_update_key_non_budget_rejects_cross_user_modification(monkeypatch):
+    """Regression: previously _check_key_admin_access was gated on
+    max_budget/spend changes only, so an internal user could rewrite any
+    OTHER field (alias, models, tpm_limit, blocked, metadata, …) on any
+    key they weren't admin of as long as they avoided budget/spend. This
+    confirms that a non-admin user updating a key that belongs to another
+    user fails with 403 even for non-budget fields."""
+    from litellm.proxy.management_endpoints.key_management_endpoints import (
+        update_key_fn,
+    )
+
+    mock_prisma_client = AsyncMock()
+    test_hashed_token = (
+        "cafebabe" * 8
+    )
+
+    mock_existing_key = MagicMock()
+    mock_existing_key.token = test_hashed_token
+    mock_existing_key.user_id = "victim_user"  # owned by someone else
+    mock_existing_key.team_id = None
+    mock_existing_key.project_id = None
+    mock_existing_key.max_budget = 10.0
+    mock_existing_key.key_alias = "original"
+    mock_existing_key.models = []
+    mock_existing_key.model_dump.return_value = {
+        "token": test_hashed_token,
+        "user_id": "victim_user",
+        "team_id": None,
+        "max_budget": 10.0,
+    }
+
+    mock_prisma_client.get_data = AsyncMock(return_value=mock_existing_key)
+    mock_prisma_client.db.litellm_verificationtoken.find_unique = AsyncMock(
+        return_value=mock_existing_key
+    )
+
+    monkeypatch.setattr("litellm.proxy.proxy_server.prisma_client", mock_prisma_client)
+    monkeypatch.setattr("litellm.proxy.proxy_server.user_api_key_cache", AsyncMock())
+    monkeypatch.setattr("litellm.proxy.proxy_server.proxy_logging_obj", MagicMock())
+    monkeypatch.setattr("litellm.proxy.proxy_server.llm_router", None)
+    monkeypatch.setattr("litellm.proxy.proxy_server.premium_user", True)
+    monkeypatch.setattr(
+        "litellm.proxy.proxy_server.hash_token", lambda t: test_hashed_token
+    )
+
+    mock_request = MagicMock()
+    mock_request.query_params = {}
+    attacker = UserAPIKeyAuth(
+        user_role=LitellmUserRoles.INTERNAL_USER,
+        api_key="sk-attacker",
+        user_id="attacker_user",  # NOT the owner
+    )
+
+    # Trying to blanket-rewrite a non-budget field on someone else's key
+    # must now fail.
+    with pytest.raises(ProxyException) as exc:
+        await update_key_fn(
+            request=mock_request,
+            data=UpdateKeyRequest(
+                key=test_hashed_token, key_alias="pwned", blocked=True
+            ),
+            user_api_key_dict=attacker,
+            litellm_changed_by=None,
+        )
+    assert str(exc.value.code) == "403"
+
+
 # ============================================================================
 # LIT-1884: Internal users cannot create invalid keys
 # ============================================================================