LibreNMS is a network monitoring system. In versions from 21.6.0 up to 26.5.0, the Signal alert transport is vulnerable to command injection because the signal-cli path and the Recipient field of an alert transport entry are insufficiently escaped before being passed to an exec call. An authenticated administrator can craft a transport entry whose Recipient contains shell metacharacters and whose path points to the bundled composer_wrapper.php script, which itself passes attacker-controlled input to further unsafe exec calls. By chaining these calls, the administrator can execute arbitrary operating-system commands on the LibreNMS host. This issue is fixed in version 26.5.0.
Affected: Packagist: librenms/librenms
### Summary A vulnerability has been identified that allows an authenticated administrator to execute arbitrary code on the host server. By adding an alert transport entry, an attacker with administrative privileges can execute malicious commands.
### Details The vulnerability is caused by an unsafe `exec` call in `deliverAlert` function of `LibreNMS/Alert/Transport/Signal.php`. Escapes for the path of `signal-cli` and the `Recipient` field are insufficient to prevent command-line injection.
The `composer_wrapper.php` under `scripts` is also vulnerable to command injection (unsafe `exec` calls) by passing the injected command as an argument, and it is accepting arguments passed by `deliverAlert`.
By chaining these unsafe `exec` calls, malicious admin user can execute any executables in the server's filesystem.
### PoC
1. Under Dashboard -> Alert -> Alert Transports
<img width="282" height="273" alt="image" src="https://github.com/user-attachments/assets/b72f55b0-b782-47d0-b4f7-75f498019345" />
2. Create a new Alert Transport entry. a. Select `Signal` as `Transport type`. b. Put `../scripts/composer_wrapper.php` into `Path`. c. Put the command to execute under `Recipient` with `;` at the start and the end of string.
<img width="767" height="391" alt="image" src="https://github.com/user-attachments/assets/5e34bfa8-4bd5-40cb-9624-0d40e40ccdc5" />
3. . Click `Save Transport`, and after the popup closed, click `Test Transport` button under `Action` of the cr…