Summary

XSS attacks occurs when application is not sanitising inputs properly and rendering the code from user input to browser which could allow an attacker to execute malicious javascript code.

PoC

1. Login
2. Create a device group in /device-groups
3. Name it as "><img src=x onerror=alert(1);>
4. save it
5. Go to services and create a service template and add that device group into that and save it
6. After that go back to device groups and delete that device, you will see XSS payload popup in message

Vulnerable code:

https://github.com/librenms/librenms/blob/63eeeb71722237d1461a37bb6da99fda25e02c91/app/Http/Controllers/DeviceGroupController.php#L173C21-L173C21

Line 173 is not sanitizing device name properly

Impact

Cross site scripting can lead to cookie stealing attacks