diff --git a/litellm/proxy/auth/auth_checks.py b/litellm/proxy/auth/auth_checks.py
index e959867091..bfcd13d909 100644
--- a/litellm/proxy/auth/auth_checks.py
+++ b/litellm/proxy/auth/auth_checks.py
@@ -512,6 +512,7 @@ async def common_checks(  # noqa: PLR0915
                 if not await _key_access_group_grants_model(
                     model=_model,
                     valid_token=valid_token,
+                    team_object=team_object,
                     llm_router=llm_router,
                 ):
                     raise
@@ -2870,20 +2871,28 @@ async def can_team_access_model(
 async def _key_access_group_grants_model(
     model: Union[str, List[str]],
     valid_token: Optional[UserAPIKeyAuth],
+    team_object: Optional[LiteLLM_TeamTable],
     llm_router: Optional[Router],
 ) -> bool:
     """
     Returns True if the key's `access_group_ids` expand to models that grant
     access to `model`. Used to let a key's access group override a team's
     model restriction in `common_checks`.
+
+    A key's access group only counts if it is also assigned to the key's team
+    (i.e., present in `team_object.access_group_ids`). This preserves the
+    team-as-owner boundary: a team member cannot escalate by naming an access
+    group that belongs to a different team.
     """
-    if valid_token is None:
+    if valid_token is None or team_object is None:
         return False
-    key_access_group_ids = valid_token.access_group_ids or []
-    if not key_access_group_ids:
+    key_access_group_ids = set(valid_token.access_group_ids or [])
+    team_access_group_ids = set(team_object.access_group_ids or [])
+    allowed_group_ids = key_access_group_ids & team_access_group_ids
+    if not allowed_group_ids:
         return False
     models_from_groups = await _get_models_from_access_groups(
-        access_group_ids=key_access_group_ids,
+        access_group_ids=list(allowed_group_ids),
     )
     if not models_from_groups:
         return False
diff --git a/tests/proxy_unit_tests/test_auth_checks.py b/tests/proxy_unit_tests/test_auth_checks.py
index 6a404712c1..026abf99d8 100644
--- a/tests/proxy_unit_tests/test_auth_checks.py
+++ b/tests/proxy_unit_tests/test_auth_checks.py
@@ -1164,6 +1164,12 @@ async def test_key_access_group_grants_model_when_group_covers_model():
         token="test-token",
         models=[],
         access_group_ids=["ryan-access-group"],
+        team_id="team-a",
+    )
+    team_object = LiteLLM_TeamTable(
+        team_id="team-a",
+        models=["mock-success"],
+        access_group_ids=["ryan-access-group"],
     )
 
     with patch(
@@ -1175,6 +1181,7 @@ async def test_key_access_group_grants_model_when_group_covers_model():
             await _key_access_group_grants_model(
                 model="claude-haiku-4-5",
                 valid_token=valid_token,
+                team_object=team_object,
                 llm_router=None,
             )
             is True
@@ -1190,11 +1197,18 @@ async def test_key_access_group_grants_model_when_key_has_no_groups():
         token="test-token",
         models=[],
         access_group_ids=[],
+        team_id="team-a",
+    )
+    team_object = LiteLLM_TeamTable(
+        team_id="team-a",
+        models=["mock-success"],
+        access_group_ids=["ryan-access-group"],
     )
     assert (
         await _key_access_group_grants_model(
             model="claude-haiku-4-5",
             valid_token=valid_token,
+            team_object=team_object,
             llm_router=None,
         )
         is False
@@ -1212,6 +1226,12 @@ async def test_key_access_group_grants_model_when_group_does_not_cover_model():
         token="test-token",
         models=[],
         access_group_ids=["other-group"],
+        team_id="team-a",
+    )
+    team_object = LiteLLM_TeamTable(
+        team_id="team-a",
+        models=["mock-success"],
+        access_group_ids=["other-group"],
     )
 
     with patch(
@@ -1223,7 +1243,76 @@ async def test_key_access_group_grants_model_when_group_does_not_cover_model():
             await _key_access_group_grants_model(
                 model="claude-haiku-4-5",
                 valid_token=valid_token,
+                team_object=team_object,
                 llm_router=None,
             )
             is False
         )
+
+
+@pytest.mark.asyncio
+async def test_key_access_group_grants_model_when_group_not_assigned_to_team():
+    """
+    Regression test: a team member naming a foreign access group on their key
+    must NOT escalate to that group's models. The group expands to the requested
+    model, but it isn't assigned to the key's team — so the override is denied.
+    """
+    from unittest.mock import AsyncMock, patch
+
+    from litellm.proxy.auth.auth_checks import _key_access_group_grants_model
+
+    valid_token = UserAPIKeyAuth(
+        token="test-token",
+        models=[],
+        access_group_ids=["team-b-premium"],
+        team_id="team-a",
+    )
+    team_object = LiteLLM_TeamTable(
+        team_id="team-a",
+        models=["mock-success"],
+        access_group_ids=["team-a-basic"],
+    )
+
+    with patch(
+        "litellm.proxy.auth.auth_checks._get_models_from_access_groups",
+        new_callable=AsyncMock,
+        return_value=["claude-opus-4-5"],
+    ) as mocked_expand:
+        assert (
+            await _key_access_group_grants_model(
+                model="claude-opus-4-5",
+                valid_token=valid_token,
+                team_object=team_object,
+                llm_router=None,
+            )
+            is False
+        )
+        # Foreign group must be filtered out before expansion ever runs.
+        mocked_expand.assert_not_called()
+
+
+@pytest.mark.asyncio
+async def test_key_access_group_grants_model_when_team_has_no_groups():
+    """Team with no access_group_ids leaves the intersection empty → denied."""
+    from litellm.proxy.auth.auth_checks import _key_access_group_grants_model
+
+    valid_token = UserAPIKeyAuth(
+        token="test-token",
+        models=[],
+        access_group_ids=["ryan-access-group"],
+        team_id="team-a",
+    )
+    team_object = LiteLLM_TeamTable(
+        team_id="team-a",
+        models=["mock-success"],
+        access_group_ids=[],
+    )
+    assert (
+        await _key_access_group_grants_model(
+            model="claude-haiku-4-5",
+            valid_token=valid_token,
+            team_object=team_object,
+            llm_router=None,
+        )
+        is False
+    )