De1CTF2019 SSRF Me

打开之后就是源码

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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)

用了python的flak框架

有三个路由:

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@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()

大概思路就是在 /De1ta 中 get param ,cookie action sign 去读取 flag.txt,其中,param=flag.txt,action 中要含有 read 和 scan,且 sign=md5(secert_key + param + action)

触及到盲区了 看一下WP

当我们访问/geneSign时,action默认为scan,而当我们通过Exec访问checkSign时,即访问getSign函数时,action为我们的cookies中的action值。

不妨假设 secert_key 是 xxx ,那么在开始访问 /geneSign?param=flag.txt 的时候,返回的 md5 就是 md5(‘xxx’ + ‘flag.txt’ + ‘scan’) ,在 python 里面上述表达式就相当于 md5(xxxflag.txtscan) ,这就很有意思了。

直接构造访问 /geneSign?param=flag.txtread ,拿到的 md5 就是 md5(‘xxx’ + ‘flag.txtread’ + ‘scan’) ,等价于 md5(‘xxxflag.txtreadscan’) ,这就达到了目标。

访问/geneSign?param=flag.txtread
得到md5

1
a99fca9514e5fd8a0e324f832e37cab7

再访问 /De1ta?param=flag.txt 并在cookie中添加
1
Cookie: action=scan;sign=a99fca9514e5fd8a0e324f832e37cab7

得到flag