# Simply Schedule Appointments <= 1.6.13.0 - Unauthenticated Stored Cross-Site Scripting via Support Page Appointment Diagnostic

- **ID:** WPSEC-2026-2884
- **Plugin:** Simply Schedule Appointments (`simply-schedule-appointments`), https://wordpress.org/plugins/simply-schedule-appointments/
- **Affected versions:** all versions before 1.6.13.4
- **Fixed in:** 1.6.13.4 (Update to 1.6.13.4 or later.)
- **Severity:** Medium 4.7 (CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N)
- **Weakness:** CWE-79
- **Usage among sites WPSec scans:** plugin Medium, affected versions Medium (as of 2026-11-12)
- **Attack surface analysis:** https://attacksurface.wpsec.com/plugin/simply-schedule-appointments
- **Fix released:** 2026-11-10
- **Published:** 2026-11-12
- **URL:** https://wpsec.com/vuln/WPSEC-2026-2884/

## Description

The Simply Schedule Appointments plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'Fix appointment durations' support diagnostic in all versions up to, and including, 1.6.13.0, due to the 'payment_method', 'customer_timezone' and 'customer_locale' booking fields being stored without sanitization and the diagnostic printing appointment rows without output escaping. This makes it possible for unauthenticated attackers who submit a booking to inject arbitrary web scripts that execute when an administrator runs the diagnostic and the affected appointment is printed to the page.

## References

- https://wpsec.com/vuln/WPSEC-2026-2884/
- https://plugins.svn.wordpress.org/simply-schedule-appointments/tags/1.6.13.4/
- https://wordpress.org/plugins/simply-schedule-appointments/

Source: WPSec, https://wpsec.com/vuln/WPSEC-2026-2884/

License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Free to use, share and adapt, also commercially, if you credit WPSec and link to this advisory.