---
id: CVE-2026-55255
title: >-
  Langflow: IDOR Vulnerability in `/api/v1/responses` Endpoint Allows
  Authenticated Attackers to Access Another User's Flow
summary: >-
  Langflow: IDOR Vulnerability in `/api/v1/responses` Endpoint Allows
  Authenticated Attackers to Access Another User's Flow
severity: critical
cvss: 9.9
cwe:
  - CWE-639
vendor: langflow
product: langflow
ecosystem: pip
affected:
  - langflow < 1.9.1
patched:
  - langflow 1.9.1
published: '2026-06-19'
updated: '2026-06-19'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-qrpv-q767-xqq2'
references:
  - url: >-
      https://github.com/langflow-ai/langflow/security/advisories/GHSA-qrpv-q767-xqq2
  - url: 'https://github.com/langflow-ai/langflow/pull/12832'
  - url: 'https://github.com/advisories/GHSA-qrpv-q767-xqq2'
tags:
  - ghsa
  - pip
  - kev
  - in-the-wild
  - exploit-available
epss: 0.00887
epssPercentile: 0.57256
ingestedAt: '2026-06-22T13:35:24.306Z'
kev: true
exploited: true
kevDateAdded: '2026-07-07'
kevDueDate: '2026-07-10'
kevRansomware: false
exploits:
  github: 1
  githubRepos:
    - 'https://github.com/rootdirective-sec/CVE-2026-55255-Lab'
  checkedAt: '2026-09-21T15:29:35.326Z'
exploitAvailable: true
---

## Overview

## 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

## Affected packages

- `langflow < 1.9.1`

## Remediation

Upgrade to a patched release:

- `langflow 1.9.1`