CVE-2026-13042 describes a stored XSS vulnerability in the yo35 RPB Chessboard WordPress plugin affecting all versions up to and including 8.1.2. The vulnerability arises from insufficient sanitization and escaping of comment content, enabling unauthenticated attackers to inject arbitrary web scripts. WordPress's built-in kses sanitization does not prevent exploitation because the malicious payload uses only allowed HTML elements and attributes, with the harmful attribute-breaking HTML generated dynamically during page rendering by the plugin's comment_text filter. This results in cross-site scripting that can execute in the context of users visiting the injected pages.

Successful exploitation allows unauthenticated attackers to execute arbitrary scripts in the browsers of users viewing affected pages, potentially leading to session hijacking, defacement, or other client-side attacks. The CVSS 3.1 base score is 7.2 (high), reflecting network attack vector, low attack complexity, no privileges or user interaction required, and impact on confidentiality and integrity but not availability.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, users should consider disabling or removing the RPB Chessboard plugin or restricting comment functionality to trusted users. Monitor the vendor's communications for updates on patches or official mitigations.