CVE-2026-0559 is a stored cross-site scripting vulnerability in the stylemix MasterStudy LMS WordPress Plugin, specifically in the 'stm_lms_courses_grid_display' shortcode. The flaw results from improper neutralization of input during web page generation, allowing authenticated users with contributor or higher privileges to inject arbitrary web scripts. These scripts execute in the context of users visiting the injected pages. The vulnerability affects all plugin versions up to 3.7.11. The CVSS 3.1 base score is 6.4 (medium), with attack vector network, low attack complexity, requiring low privileges but no user interaction, and impacts confidentiality and integrity with no availability impact. No official patch or vendor advisory is provided in the data, and no known exploits have been reported.

An attacker with contributor-level access or higher can inject malicious scripts into pages via the vulnerable shortcode. These scripts execute in the browsers of users who visit the affected pages, potentially leading to unauthorized actions such as session hijacking or data theft. The impact affects confidentiality and integrity but does not affect availability. No known exploitation in the wild has been reported.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, restrict contributor-level access to trusted users only and consider disabling or limiting use of the 'stm_lms_courses_grid_display' shortcode to reduce exposure. Monitor official stylemix communications for updates or patches addressing this vulnerability.