The Simple Calendar – Google Calendar Plugin for WordPress suffers from a reflected XSS vulnerability due to the use of add_query_arg without proper escaping of URL parameters. This allows unauthenticated attackers to inject arbitrary web scripts that execute when a victim interacts with a maliciously crafted URL. The issue affects all versions up to 3.4.2. The vulnerability is identified as CWE-79 and has a CVSS 3.1 base score of 6.1, indicating a medium severity. No known exploits in the wild have been reported, and no patch or remediation details are currently available.

Successful exploitation can lead to the execution of arbitrary scripts in the context of the affected website, potentially allowing attackers to steal user credentials, perform actions on behalf of the user, or conduct other malicious activities limited to the scope of the user's browser session. The vulnerability requires user interaction (clicking a crafted link) and does not require authentication.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, users should exercise caution when clicking on links related to the Simple Calendar plugin and consider disabling or restricting the plugin if possible. Monitoring vendor channels for updates is recommended.