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).
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
## Vendor Response
This issue has been responsibly disclosed to the vendor for which a patch has been released in version 2.3.24
Appsecco Security Team
18th May 2019: Discovered and reported to vendor
21st May 2019: Vendor confirmation
23rd July 2019: Fixed version (2.3.24) released
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