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## Introduction  
  
### Description  
  
A remotely exploitable vulnerability exists in the 2.3.23-119-GA version of Sangoma SBC that would allow an unauthenticated user to create a privileged user on the system using the web application login interface.  
  
### Vulnerability Type  
  
- Argument Injection or Modification (https://cwe.mitre.org/data/definitions/88.html)  
  
## Product Overview  
  
A Sangoma SBC protects both your data and voice network and is designed to handle every aspect of phone calls that travel over the internet (or voice-over-ip phone calls).  
  
## Background  
  
The Sangoma SBC web application heavily relies on the python script `/usr/local/sng/bin/sng-user-mgmt` for various user operations including authenticating the user that is supplied on the login screen of the web application.  
  
When a username and password is provided to the application, it is processed by `/var/webconfig/gui/Webconfig.inc.php` which uses the `Execute` function from `/var/webconfig/api/ShellExec.class.php` to pass the credentials to `/usr/local/sng/bin/sng-user-mgmt` as arguments. The `Execute` function applies the `escapeshellcmd` function to convert any shell characters as literals, however there is no verification that the variables passed do not contain strings that can be interpreted as additional arguments to `/usr/local/sng/bin/sng-user-mgmt`.  
  
For example, when a username `root` and password `secure` is passed to the application, the final command that is created by `Execute` to be run is `/usr/local/sng/bin/sng-user-mgmt --action=login --user=ha --encrypted-password=ENCPASS(secure)`  
  
By inspecting the code and help menu of `/usr/local/sng/bin/sng-user-mgmt`, we see that the `action` parameter supports other modes which includes `add` that creates a user. The `-o` option can be used to make the user have sudo privileges when `--action=add` is used.  
  
Passing additional arguments through the username field results in a new privileged user being created on the system.  
  
## Proof of Concept Exploit  
  
1. Pass a username with the value `john --action=add -p StrongPass1 -o`  
2. The password field can be set to anything as this will be ignored  
3. Click login  
4. A local user with sudo privileges called `john` with password `StrongPass1` will be created  
5. An attacker can SSH into the machine with these credentials or login via the web console  
  
## Versions Tested  
  
- 2.3.23-119-GA  
  
## Vendor Response  
  
This issue has been responsibly disclosed to the vendor for which a patch has been released in version 2.3.24  
  
https://wiki.sangoma.com/display/SBC/SBC+Downloads  
  
## Credits  
  
Appsecco Security Team  
http://www.appsecco.com  
  
## Timeline  
  
18th May 2019: Discovered and reported to vendor  
21st May 2019: Vendor confirmation  
23rd July 2019: Fixed version (2.3.24) released  
  
## Reference  
  
- [https://www.sangoma.com/products/sbc/](https://www.sangoma.com/products/sbc/)  
  
  
Riyaz Walikar  
  
+91 9886042242  
  
<http://www.appsecco.com/>www.appsecco.com<http://www.appsecco.com/>  
  
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