# Simply Schedule Appointments <= 1.6.13.0 - Unauthenticated Availability Check Bypass via 'start_date' Parameter

- **ID:** WPSEC-2026-2885
- **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 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N)
- **Weakness:** CWE-20
- **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-2026-2885/

## Description

The Simply Schedule Appointments plugin for WordPress is vulnerable to an availability check bypass via the 'start_date' parameter in all versions up to, and including, 1.6.13.0 due to improper validation of the date format when creating or updating appointments. A non-canonical value such as one with a ' +1 day' suffix is parsed by PHP as a different moment than the date MySQL stores. This makes it possible for unauthenticated attackers to create appointments in slots that are already booked or otherwise unavailable, resulting in double-bookings.

## References

- https://wpsec.com/vuln/WPSEC-2026-2885/
- 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-2026-2885/

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.