ssrfme

本文最后更新于:2022年11月4日 下午

这题说实话很简单,只是考察了一个trick,奈何我没了解过这个,记录一下

因为题目给出代码的方式过于阴间(如下),就直接去github看代码了

image-20221104161114604

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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')

简单的flask应用,功能一眼就能看明白,根路由给看代码,genesign给注册,De1ta给执行read或者scan,但是这里scan是写死的,这里就不得不提到这个trick了,也就是哈希长度拓展攻击,原理大概就是"abc"+"def"="abcd"+"ef"

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

也就是说这里第一次请求result.txt的时候,把param填为flag.txtread,action默认是scan,

当我们第二次请求时,使param为flag.txt,此时action即为readscan,也就是同时包含read和scan,先执行scan时程序并没有直接return,后面再执行read,使返回的json中外带了data的数据,最终读取到flag.txt。

image-20221104171101753


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