Simply Schedule Appointments Plugin up to 1.6.12.2 on WordPress Notification Rendering wp_kses_post cross site scripting

Summaryinfo

A vulnerability was found in Simply Schedule Appointments Plugin up to 1.6.12.2. It has been classified as problematic. The affected element is the function wp_kses_post of the component Notification Rendering. Performing a manipulation results in cross site scripting. This vulnerability is reported as CVE-2026-13400. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability, which was classified as problematic, was found in Simply Schedule Appointments Plugin up to 1.6.12.2. This affects the function wp_kses_post of the component Notification Rendering. The manipulation with an unknown input leads to a cross site scripting vulnerability. CWE is classifying the issue as CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. This is going to have an impact on integrity. The summary by CVE is:

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.

It is possible to read the advisory at wpscan.com. This vulnerability is uniquely identified as CVE-2026-13400 since 06/26/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. It demands that the victim is doing some kind of user interaction. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1059.007 according to MITRE ATT&CK.

Upgrading to version 1.6.12.4 eliminates this vulnerability.

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Productinfo

Type

• WordPress Plugin

Name

• Simply Schedule Appointments Plugin

Version

• 1.6.12.0
• 1.6.12.1
• 1.6.12.2

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