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Buuoj SSRF Me 题解

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昨天做到的一个很好的题目（个人觉得），写出来给大家看看（

打开靶机

打开靶机，直接看到源码，并且能够看到提示，flag在flag.txt内：

但是这源码也太恶心人了吧，这谁看得懂啊…

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#! /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',port=80)

然后经过我不懈的努力（雾

把源码整理好了：

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#非常优质的题目属于是，考对代码的审计能力（认真读）
#源码如下：
#! /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')

审代码

接下来慢慢对代码进行审计即可：

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#flask类题目，给源码，结合题目SSRF，需要我们进行代码的审计，首先读路由：
@app.route("/geneSign", methods=['GET', 'POST'])
def geneSign():
    param = urllib.unquote(request.args.get("param", ""))
    action = "scan"
    return getSign(action, param)
#genesign路由，通过get传入param参数，action = sign，然后返回函数getSign的结果


@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())
#De1ta路由，cookie传入action sign、get传入param，如果通过waf，执行exec

@app.route('/')
def index():
    return open("code.txt","r").read()
#显示源码
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#然后是函数：
def getSign(action, param):
    return hashlib.md5(secert_key + param + action).hexdigest()
#getSign函数，返回字符串secret_key与param与action拼接的md5结果

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

def waf(param):
    check=param.strip().lower()
    if check.startswith("gopher") or check.startswith("file"):
        return True
    else:
        return False
#waf：过滤gopher和file
    def Exec(self):
        result = {}
        result['code'] = 500
        if (self.checkSign()):#如果checkSign通过
            if "scan" in self.action:
                tmpfile = open("./%s/result.txt" % self.sandbox, 'w')
                resp = scan(self.param)#有scan在action内时，执行scan方法，将param的结果储存到result.txt内
                if (resp == "Connection Timeout"):
                    result['data'] = resp
                else:
                    print resp
                    tmpfile.write(resp)
                    tmpfile.close()
                result['code'] = 200
            if "read" in self.action:#有read在action内时，执行read方法，读取result.txt的结果
                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):#检查如果getSign()后的结果=sign时，回显true
        if (getSign(self.action, self.param) == self.sign):
            return True
        else:
            return False

获取flag

整理一下大概就是如下的思路：

通过exec函数读取flag.txt的内容，而flag.txt的内容会被scan的action存储在result.txt中

我们只需要获得read方法读取即可：

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flag的内容可以通过scan函数储存，read函数读取-->
action中需要有readscan-->
又需要checkSign通过-->
getSign(self.action, self.param) == self.sign -->
而getsign又返回hashlib.md5(secert_key + param + action).hexdigest()-->
等价于hashlib.md5(secert_key + param + action).hexdigest()==self.sign

sign，action在/De1ta路由中由cookie传入，而param由get方法传入

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action=readscan,sign=一个md5值
-->/geneSign会返回secret_key+param+scan的md5
-->param=flag.txtread，成功获取sign
-->/De1ta中param=flag.txt,action=readscan,符合checkSign，又有read和scan，就会输出flag

所以我们需要先访问/geneSign路由，然后param=flag.txtread

返回一个值：(055967a25e4ba3f082a3ab94e0344994)

注：这个值随每次靶机打开都是不一样的

这个值就是flag.txtreadscan的sign值：

而我们传入的参数param，action又是flag.txt、readscan，完美符合sign值

然后使用bp抓包，添加cookie，修改url即可：

结束~

另解：哈希长度拓展攻击

虽然但是我并不知道这个怎么用，在这里贴出大佬的wp吧（

略略水一篇博客没人骂我的吧~

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