The Membership Plugin – Restrict Content WordPress plugin suffers from a stored cross-site scripting vulnerability (CWE-79) due to improper neutralization of input during web page generation. Specifically, the plugin fails to adequately sanitize and escape user-supplied attributes in the 'register_form' and 'restrict' shortcodes, allowing authenticated users with contributor-level permissions or higher to inject malicious scripts. These scripts persist in the plugin's stored content and execute in the context of users who access the compromised pages. This vulnerability affects all plugin versions up to 3.2.15. The CVSS 3.1 base score is 6.4, reflecting network attack vector, low attack complexity, required privileges at the contributor level, no user interaction, and partial impact on confidentiality and integrity but no impact on availability.

An attacker with contributor-level or higher access can inject persistent malicious scripts into pages via vulnerable shortcodes. These scripts execute in the browsers of users who visit the affected pages, potentially leading to unauthorized actions or data disclosure within the context of the victim's session. The impact is limited to confidentiality and integrity with no availability impact. No known exploitation in the wild has been reported.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Since no official patch or fix information is provided, users should monitor the vendor's communications for updates. Until a fix is available, restrict contributor-level access to trusted users only and consider disabling or limiting use of the vulnerable shortcodes ('register_form' and 'restrict') to reduce exposure.