CVE-2026-16155 describes a cross-site scripting vulnerability in SourceCodester Class and Exam Timetabling System 1.0. The vulnerability is located in the /schoolyr.php file where the 'sy' argument is not properly sanitized, enabling remote attackers to execute arbitrary scripts in the context of the affected application. The exploit is publicly available, but there is no indication of active exploitation in the wild. The vulnerability requires low attack complexity and no privileges but involves user interaction.

Successful exploitation of this vulnerability could allow an attacker to execute arbitrary scripts in the victim's browser, potentially leading to session hijacking, defacement, or redirection to malicious sites. However, the impact is limited by the requirement for user interaction and the lack of privilege escalation or system compromise.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, users should consider applying input validation or sanitization on the 'sy' parameter at the application level to mitigate the risk. Additionally, employing web application firewalls (WAFs) that detect and block XSS payloads may reduce exposure.