CVE-2026-59163

Auth bypass: JWT signature verification disabled, allowing any token.

• CVSS 9.1
• 347
• Authentication, Authorization, and Session Management
• Remote

Mnemosyne is a memory layer for artificial intelligence agents. Prior to v3.10.1, the auth check in mnemosyne/core/sync_server.py parsed the JWT's header and payload using base64 decoding, then passed the token to a jwt library call with options that effectively disabled signature verification. The server accepted any well-formed token regardless of the signature, including tokens with alg: none and tokens signed with the wrong key. The fix in v3.10.1 replaces the broken decode with a from-scratch HS256 verifier using only the Python standard library. For users who cannot upgrade immediately, restrict network access to the sync server endpoint to trusted clients only. Firewall, reverse proxy with mTLS, or localhost bind with SSH tunnel are all viable. The vulnerability is not exploitable against an unreachable endpoint.

CVE

CVE-2026-59163

CWE

347

CVSS base score

9.1

Published

2026-09-18

OWASP

A07 Identification and Authentication Failures

Orthogonal defect classification

Checking

Code defect classification

Incorrect Check

Category

Authentication, Authorization, and Session Management

Subcategory

Insecure Authentication Mechanisms

Accessibility scope

Remote

Impact

Unauthorized Access

Affected component

Python

Fixed by upgrading

Yes

Solution

Upgrade to mnemosyne v3.10.1 or later.

import base64
import json
import jwt  # PyJWT library

def verify_token(token: str, secret: str) -> bool:
    # VULNERABLE: disables signature verification
    header_b64, payload_b64, signature_b64 = token.split('.')
    header = json.loads(base64.urlsafe_b64decode(header_b64 + '=='))
    payload = json.loads(base64.urlsafe_b64decode(payload_b64 + '=='))
    # Decode with verification disabled
    try:
        jwt.decode(token, options={"verify_signature": False})
        return True
    except jwt.InvalidTokenError:
        return False

import base64
import json
import hmac
import hashlib

def verify_token(token: str, secret: str) -> bool:
    # FIX: proper HS256 signature verification
    try:
        header_b64, payload_b64, signature_b64 = token.split('.')
        signing_input = f"{header_b64}.{payload_b64}".encode()
        signature = base64.urlsafe_b64decode(signature_b64 + '==')
        expected_sig = hmac.new(secret.encode(), signing_input, hashlib.sha256).digest()
        if not hmac.compare_digest(signature, expected_sig):
            return False
        json.loads(base64.urlsafe_b64decode(header_b64 + '=='))  # ensure valid JSON
        json.loads(base64.urlsafe_b64decode(payload_b64 + '=='))
        return True
    except Exception:
        return False

__VAITP_MODEL_REFUSED__

@misc{vaitp:cve202659163,
  title        = {{Auth bypass: JWT signature verification disabled, allowing any token.}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2026},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2026-59163},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2026-59163/}}
}