[De1CTF 2019]SSRF Me

[De1CTF 2019]SSRF Me

python-flask框架学习笔记(一)–route(路由):https://blog.csdn.net/weixin_44923175/article/details/89339607
直接分析源代码

#! /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
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')

是个用python写的后端程序,web的flash框架,那就先看路由(route)

  • 先看geneSign,基本信息:上传方法有get和post 上传的参数为param与其他字符串拼接,然后进行的操作action是扫描(scan),进入getsign(这里还不知道这个sign的作用),到了下边[De1CTF 2019]SSRF Me

  • -他是用param和action做拼接的!而action是固定的scan ,也就是说,我们先使用geneSign,传参为flag.txtread,这样只会param+action拼接为 flag.txtreadscan,生成sign保存下来

  • 再看De1ta,这个应该是重点,

    action = urllib.unquote(request.cookies.get("action"))
    param = urllib.unquote(request.args.get("param", ""))
    sign = urllib.unquote(request.cookies.get("sign"))
    

    这里的action和sign的request都是在cookie中执行的,这里的sign应该就是需要上一步的操作得到,然后这里的param和上一步的一样。

    执行之后传到task返回Exec()。

  • 再分析task里的exec(),里边还有两个if,然后2个if,判断scan或read 是否在action内,在则,前者是把param对应文件的内容写入result.txt,后者是把result.txt取出来并返还给我们,也就是说,这2个if我们都需要调用,这样就能获取到flag,而scan和read的判断是包含,所以我们的action就可以是readscan,或者scanread

  • 再来看getSign(self.action, self.param) == self.sign,直接看getSign, param+action=“flag.txt” + “readscan”=“flag.txtreadscan”

    这样形成的sign刚好就能对应到。而这样又能将param中文件内容读出并返回给我们,以此获取flag
    [De1CTF 2019]SSRF Me
    sign=bb6563b7ec0913efbad4e0626e5897bb
    [De1CTF 2019]SSRF Me
    flag{87c2c2d9-61aa-4b52-81de-ef7403bdede9}

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