Affected: IBM Langflow OSS

IBM Langflow OSS contains a weak cryptographic key derivation vulnerability in the ensure_fernet_key() function.

Affected: PyPI: langflow

### Summary

Langflow uses Python's `random` module (Mersenne Twister, a non-cryptographic PRNG) seeded with the `SECRET_KEY` to derive the Fernet encryption key for all stored user credentials (API keys, LLM provider secrets, database passwords). When the `SECRET_KEY` is shorter than 32 characters — a common scenario for self-hosted deployments using simple/memorable secrets — the derived encryption key is fully deterministic and reproducible by anyone who knows the seed value. An attacker who obtains the `SECRET_KEY` (e.g., via the MCP path traversal in this repo) can reconstruct the exact Fernet key offline and decrypt every credential stored in the database with no brute force required.

Even when `SECRET_KEY` is 32+ characters (the "safe" branch), the raw key material is used directly as the Fernet key — meaning exfiltrating the `secret_key` file is sufficient to decrypt all credentials without any additional computation.

**Severity:** Critical — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N (9.1) **CWE-338:** Weak PRNG | **CWE-321:** Hard-coded Cryptographic Key | **CWE-311:** Missing Encryption of Sensitive Data

### Details

**Root cause: `src/backend/base/langflow/services/auth/service.py`, lines 651–663**

```python MINIMUM_KEY_LENGTH = 32

def _ensure_valid_key(self, raw_key: str) -> bytes: if len(raw_key) < MINIMUM_KEY_LENGTH: random.seed(raw_key) # Non-cryptographic PRNG seeded with the secret key = bytes(ran…