Langflow: insecure direct object reference

## 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)](https://github.com/langflow-ai/langflow/blob/v1.9.0/src/backend/base/langflow/helpers/flow.py#L399C1-L414C67). 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`](https://github.com/langflow-ai/langflow/blob/v1.9.0/src/backend/base/langflow/api/v1/openai_responses.py#L589)). ## 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

CVSS 3.1

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L

Severity from

GitHub (reviewed advisory)

Weakness

CWE-639

Also known as

CVE-2026-55255, PYSEC-2026-221

• github.com/langflow-ai/langflow/security/advisories/GHSA-qrpv-q767-xqq2
• nvd.nist.gov/vuln/detail/CVE-2026-55255
• github.com/langflow-ai/langflow/pull/12832
• github.com/langflow-ai/langflow/commit/2c9f498d664a3c32698b57d7c5e752625291060e
• github.com/langflow-ai/langflow
• github.com/pypa/advisory-database/tree/main/vulns/langflow/PYSEC-2026-221.yaml
• webflow.sysdig.com/blog/understanding-langflow-cve-2026-55255-and-why-higher-cvss-vulnerabilities-arent-always-the-most-exploited
• www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55255