IPFire < v2.29 Stored XSS via Default Time Sync

IPFire versions prior to 2.29 (Core Update 198) contain a stored cross-site scripting (XSS) vulnerability that allows an authenticated attacker to inject arbitrary JavaScript code through the UPDATE_VALUE parameter when updating the default time synchronization settings. When the default values displayed on the Time Server page are updated, the application issues an HTTP POST request to /cgi-bin/time.cgi, and the synchronization value is provided in the UPDATE_VALUE parameter. The value of this parameter is stored and later rendered in the web interface without proper sanitation or encoding, allowing injected scripts to execute in the context of other users who view the affected Time Server configuration page.