CVE-2026-13400 Simply Schedule Appointments < 1.6.12.4 - Unauthenticated Stored XSS via Booking Customer Information
Unauthenticated attackers can inject malicious scripts via booking information, leading to code execution or account takeover in Simply Schedule Appointments.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-13400?
CVE-2026-13400 is a medium-severity cross-site scripting vulnerability in Unknown Simply Schedule Appointments, published on 27 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Simply Schedule Appointments is vulnerable to unauthenticated Stored Cross-Site Scripting in all versions up to and including 1.6.12.2. The root cause is a sanitization-ordering defect: the rendered notification content is decoded back into live HTML after it has already passed through the Simply Schedule Appointments WordPress plugin before 1.6.12.4's wp_kses_post() filter, so a double-encoded payload survives intake and is reintroduced as an executable element at render time.
Weakness: CWE-79
Which versions are affected by CVE-2026-13400?
How do I fix CVE-2026-13400?
No fix has been published for CVE-2026-13400 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-13400 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-13400 exists.
Sources
Also known as GHSA-v365-26q9-f844.