Tuesday, August 1, 2017

Silently Fixed Unauthorized Command Injection in WAGO PLC Ethernet

It's been almost 4 years I didn't blogged anything on anywhere (shame).

Anyway, recently found Unauthorized Command Injection vulnerability in WAGO PLC's web-based management software. Affected device is here (WAGO 750-8202 PFC200 CS 2ETH RS).

P.S: This is not related with CVE-2016-9362.

You would need following tools if you would like to analyze vulnerability by yourself;
  • Burp Suite 
  • A Web Browser 
  • Binwalk 
  • Code Editor (My fav is Sublime Text, it's so lightweight and have good themes) 
If you fire up your MITM proxy (Burp Suite is my choice) and visit web application, eventually you will notice that application do lots of XML HTTP Requests and one of requested URL is /wbm/configtools.php. That endpoint executes some OS commands and shares output with the web application (I know 90's wants it's vulnerabilities back).

While playing with JSON payload sent to configtools.php endpoint, find out that it's possible to inject OS commands into "parameter" JSON value. Injected commands such as uname -a and id.

Results of executed commands.

Bingo! Easy and quick win against a dummy device web-based management software.

To confirm that critical vulnerability in latest version of firmware, simply downloaded the latest firmware from WAGO's web site, extracted it with binwalk (thanks authors of binwalk) and start to review source code.

In the source code, CallConfigtoolByJson function called to JSON request from browser which later call CallConfigtool function to process "parameter" value in JSON payload.

OK, commments and code fixes show that they found it internally (maybe?) and fixed it silently. Requested old firmwares but they didn't send me yet :)

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