CVE-2026-15726 describes a stored Cross-Site Scripting vulnerability in the Serious Slider plugin for WordPress, affecting all versions up to and including 1.4.0. The flaw exists in the handling of the 'theme' shortcode attribute, where input is not properly sanitized or escaped before being rendered on web pages. This allows authenticated attackers with contributor or higher privileges to inject arbitrary JavaScript code that executes in the context of users visiting the compromised pages.

Successful exploitation allows an attacker with contributor-level access or higher to execute arbitrary scripts in the browsers of users who view the injected pages. This can lead to session hijacking, defacement, or other client-side attacks. The vulnerability does not affect availability and requires authentication with limited privileges.

No official patch or remediation level has been confirmed at this time. Users should monitor the vendor's advisory for updates. Until a fix is available, restrict contributor-level access to trusted users and consider disabling or removing the Serious Slider plugin if possible to reduce risk.