The Simply Schedule Appointments plugin contains a stored cross‑site scripting flaw that occurs when an authenticated user with contributor privileges or higher inserts malicious data into the shortcode attributes ssa_admin_upcoming_appointments, ssa_admin_upcoming_appointments and ssa_past_appointments. The plugin fails to properly sanitize and escape user supplied attributes, leading to arbitrary script injection. Once stored, the injected code executes whenever a page containing the shortcode is rendered for any site visitor, potentially allowing attackers to hijack sessions, deface content or redirect users to malicious sites.

The vulnerability affects the croixhaug:Appointment Booking Calendar — Simply Schedule Appointments Booking Plugin for WordPress. All released versions up to and including 1.6.8.30 are impacted; later releases beyond 1.6.8.30 are presumed fixed and are not listed.

The CVSS score of 6.4 indicates a moderate severity level, while the EPSS score of less than 1 % suggests that the probability of exploitation is currently low. The flaw is not listed in the CISA KEV catalog, implying that no widespread exploits are publicly known. Attackers require authenticated access at the contributor level or higher to inject the malicious payload, meaning that anyone with such privileges to the WordPress administrative interface could perform the exploit. The impact remains confined to users who view pages containing the affected shortcodes, but the execution of arbitrary scripts can compromise session data and the integrity of the site.