de1ctf-ssrfme(哈希长度拓展攻击)

给出代码:

#! /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,port=80)

最后的flag在flag.txt中。

这段代码是用flask框架写的,因此flask的关键点在于对于路由(route)的使用。

看一下这三个路由

#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()

进入getsign可以调用scan方法,进入/De1ta可以get params,最终带着cookie去访问code.txt。

拓展攻击位置

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

EXEC方法:

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

判断action里是否有scan,如果有的话则将scan读到的内容写进沙盒里的result.txt;如果read在action里,则将沙盒里的result.txt的内容读出来。

分析完代码我们发现getSign默认只生成action为scan的签名,我们可以利用将flag.txt的内容读到result.txt里,如果我们想要将result.txt的内容读出来则需要伪造一个action为read的签名。
计算hash的值

访问http://192.168.1.104:32768/geneSign?params=flag.txt

拿到了初始的md5值现在需要伪造使等式成立。

分享图片

 

因此最终需要携带伪造的cookie访问/De1ta?param=flag.txt才可以读取flag

exp:

import requests

url = http://web68.buuoj.cn/De1ta?param=flag.txt

##将生成\x转换成%
cookies = {
 sign=1e596ed4d19d9b2d6142b011b2af2cbd; action=scan%80%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%e0%00%00%00%00%00%00%00mario
}
res = requests.get(url=url, cookies=cookies) print(res.text)
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