De1CTF Ssrfme 详解
由于比赛期间去培训了，没有参加比赛，复盘一下
FLASK框架
http://139.180.128.86/
一上来给了源码
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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',port=80)
|
访问http://139.180.128.86/geneSign?param=1
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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)
...
def getSign(action, param):
return hashlib.md5(secert_key + param + action).hexdigest()
|
能得到md5(secert_key + param + action)
在scan函数
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| def scan(param):
socket.setdefaulttimeout(1)
try:
return urllib.urlopen(param).read()[:50]
except:
return "Connection Timeout"
|
param可控，盲猜这里就是ssrf的点
然后De1ta路由
自己补上cookie和param，会发送请求，调用scan函数
会有checkSign函数，先带着param访问/geneSign注册sign
接着带着sign和param，cookie访问/De1ta
/etc/passwd的返回值是200
得到flag.txt的sign
接着访问De1ta
为什么没有返回值呢，发现，好像不能用scan函数，需要调用read
否则只能拿到statuscode
但是在getsign里，action=scan是写死了的,后面获取的md5值，带入的action也就是scan
bypass waf
在waf里
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| def waf(param):
check=param.strip().lower()
if check.startswith("gopher") or check.startswith("file"):
return True
else:
return False
|
检测了禁止以file开头来读文件
试了%00,%0a都没用
假如，我们传入的param是flag.txtread
得到的md5值如下
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md5(secert_keyflag.txtreadscan)
|
这样，我们只要让action=readscan
在Exec做检测的时候，就能进入判断
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| if "read" in self.action:
|
action = readscan
所以payload
拿到flag
