buu de1tactf ssrfme
正好更新了ssrf上一题来加深印象，这题难度适中，就是要捋清楚漏洞利用的逻辑链条，打ctf嘛，没有一个清晰的思路是不行的
贴源码:
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|
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)):
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
@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')
|
审计
很显然这个是flask框架搭建起来的web，要对其进行代码审计，首先看路由函数
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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()
|
一个一个路由来看
接着跟进查看相关函数 /geneSign 相关的getsign()没啥可看的，就是一个生成签名，但是要注意的是param在前，action在后，直接看waf()限制不能使用gopher和file协议，接下来就是test对象的内置的exec()函数了，首先使用checkSgin()进行判断如果传入的action(challenge中通过cookie获取)和param(challenge中通过get方法获得)生成的签名和sign(challenge中通过cookie获取)进行比较，如果是相同的话则进入下一步判断如果scan在”action”中的话那么可以通过scan方法对param传入的值进行urlopen读取文件之后将读取的内容写入一个临时文件中如果read在”action”中的话，那么会读取前面的临时文件的内容
思路
我们来捋一捋，action中必须要有scan和read，而且这两个值要和param进行拼接之后生成的md5签名要相同，题目提示flag在flag.txt那么我们肯定想要urlopen(flag.txt),所以我们在访问/De1ta路由的时候传入参数/De1ta?param=flag.txt 通过cookie传入”scanread”或者”readscan”当然你也可以传入”scanxxxreadxxx”等格式只要保证scan和read在action中即可，这两个条件都满足，我们来看看sign hashlib.md5(secert_key + flag.txt + readscan(scanread) ).hexdigest(),要和这个sign的值一致，所以我们就访问/geneSign路由因为/geneSign已经限定了action的值为scan那么我们跟进getSign()查看，加密的字符串为hashlib.md5(secert_key + param + scan).hexdigest(),那么要构成和上面的sign一致的值得话我们只能传入param=flag.txtread变成 hashlib.md5(secert_key + flag.txtread + scan ).hexdigest(),这样就能保持一致了
payload
