Is CVE-2026-13400 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-13400 being exploited in the wild.

How severe is CVE-2026-13400?

Informational severity, with a CVSS score of 0, published 27 July 2026.

Which products and versions are affected?

Simply Schedule Appointments up to and including 1.6.12.2.

Is there a fix for CVE-2026-13400?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is CVE-2026-13400 attacked?

It is attacked over the network, in a web application.

Am I affected by CVE-2026-13400?

Check whether you run Simply Schedule Appointments at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-13400: Simply Schedule Appointments Stored XSS in Booking Customer Information

CVE-2026-13400 · Severity: info · CVSS 0 · Published 2026-07-27

Simply Schedule Appointments, a popular WordPress plugin used for managing bookings and schedules, contains a security flaw that allows unauthenticated visitors to inject malicious scripts into the system. By submitting a specially crafted booking request, an attacker can store a hidden script that executes whenever an administrator views the booking details or notification previews. This could allow an attacker to hijack administrative sessions, steal sensitive cookies, or perform unauthorized actions on the website.

Technologies: Simply Schedule Appointments. Vendors: Simply Schedule Appointments.

Quick answers

Is CVE-2026-13400 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-13400 being exploited in the wild.
How severe is CVE-2026-13400?: Informational severity, with a CVSS score of 0, published 27 July 2026.
Which products and versions are affected?: Simply Schedule Appointments up to and including 1.6.12.2.
Is there a fix for CVE-2026-13400?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-13400 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-13400?: Check whether you run Simply Schedule Appointments at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A Stored Cross-Site Scripting (XSS) vulnerability exists in Simply Schedule Appointments versions <= 1.6.12.2. The root cause is a sanitization-ordering defect where rendered notification content is decoded back into live HTML after passing through the wp_kses_post() filter. An unauthenticated attacker can submit a double-encoded payload (e.g., &lt;img src=x onerror=...&gt;) via the public booking REST API endpoint (/wp-json/ssa/v1/appointments). Because the payload is double-encoded, it survives the initial intake sanitization; however, the plugin's notification preview mechanism subsequently decodes the entities, reintroducing executable HTML elements into the DOM via v-html (innerHTML). This allows for arbitrary JavaScript execution in the context of an authenticated administrator. The issue is addressed in version 1.6.12.4.

Affected products

Simply Schedule Appointments Simply Schedule Appointments up to and including 1.6.12.2

Timeline

2026-07-27: advisory: Vulnerability disclosed via WPScan and NVD
2026-07-27: disclosed

References

https://wpscan.com/vulnerability/501b2929-3216-4587-8124-088fd51becf1/

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.