GHSA-qrpv-q767-xqq2 Langflow: IDOR Vulnerability in `/api/v1/responses` Endpoint Allows Authenticated Attackers to Access Another User's Flow

• PyPI langflow: < 1.9.1 → fixed in 1.9.1

Summary Insecure Direct Object Reference (IDOR) vulnerability in `/api/v1/responses` endpoint allows an authenticated attacker to execute any flow belonging to another user by specifying the victim's flow ID in the request. Details The vulnerability exists in the `get_flow_by_id_or_endpoint_name` helper function in `src/backend/base/langflow/helpers/flow.py` (lines 399-414). When a flow is accessed via UUID (flow_id), the function queries the database directly without verifying if the authenticated user owns that flow: ```python src/backend/base/langflow/helpers/flow.py:399-414 async def get_flow_by_id_or_endpoint_name(flow_id_or_name: str, user_id: str | UUID | None = None) -> FlowRead: async with session_scope() as session: try: flow_id = UUID(flow_id_or_name) # When using UUID, query directly WITHOUT checking user_id flow = await session.get(Flow, flow_id) # ❌ No user_id check! except ValueError: endpoint_name = flow_id_or_name stmt = select(Flow).where(Flow.endpoint_name == endpoint_name) # Only when using endpoint_name is user_id checked if user_id: stmt = stmt.where(Flow.user_id == uuid_user_id) ``` This function is used by the `/api/v1/responses` endpoint (defined in `src/backend/base/langflow/api/v1/openai_responses.py:589`). PoC (Proof of Concept) ```bash Attacker (user A) with API_KEY_A tries to execute victim (user B)'s flow curl -X POST "http://localhost:7860/api/v1/responses" \ -H "x-api-key: sk-ATTACKER_API_KEY" \ -H "Content-Type: application/json" \ -d '{ "model": "VICTIM_FLOW_ID", "input_value": "test", "stream": false }' Returns 200 and executes the victim's flow ``` Impact Any authenticated user can: 1. Execute any flow in the system by knowing its flow ID 2. Access potentially sensitive data processed by victim's flows 3. Consume victim's resources Fixes Fixed in PR #12832 (`fix(security): close IDOR in get_flow_by_id_or_endpoint_name`), merged 2026-04-22, released in Langflow 1.9.1. The helper normalizes `user_id` once and enforces ownership on both lookup branches (UUID *and* `endpoint_name`): ```python flow_id = UUID(flow_id_or_name) flow = await session.get(Flow, flow_id) if flow is not None and uuid_user_id is not None and flow.user_id != uuid_user_id: flow = None # cross-user lookup falls through to the shared 404 ``` Key points: • Cross-user lookups return 404 (not 403), so flow existence is not disclosed via a 403-vs-404 oracle. • `/api/v1/responses` and `/api/v2/workflow` pass `user_id` explicitly, so fixing the helper closes them directly; the `/api/v1/run*` routes were additionally moved from a bare `Depends(get_flow_by_id_or_endpoint_name)` to auth-aware wrapper dependencies (defense in depth). • A malformed `user_id` now fails closed (404 instead of a raw 500). • Webhook routes intentionally keep the unscoped lookup (public by design / explicit ownership check elsewhere). • Regression tests cover the cross-user UUID case and reproduce the original PoC against `/api/v1/responses`. Acknowledgements Thanks to the security researchers who responsibly disclosed this vulnerability: • @yzeirnials • @johnatzeropath • @LeftenantZero • @Zwique