The Simple Shopping Cart plugin for WordPress (mra13) suffers from a stored cross-site scripting vulnerability (CWE-79) due to improper neutralization of input during web page generation. Specifically, the 'wp_cart_button' shortcode does not adequately sanitize or escape user-supplied attributes, allowing authenticated users with contributor or higher privileges to inject malicious scripts. These scripts are stored and executed when other users access the injected pages. This vulnerability affects all plugin versions up to 5.1.3. The CVSS 3.1 vector is AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N, reflecting network attack vector, low attack complexity, requiring privileges, no user interaction, scope changed, and low impact on confidentiality and integrity, with no impact on availability.

An attacker with contributor-level or higher access can inject persistent malicious scripts into pages via the vulnerable shortcode. These scripts execute in the context of users viewing the pages, potentially leading to unauthorized actions or data exposure limited to the scope of the injected script. The confidentiality and integrity impacts are low, and availability is not affected. There are no reports of active exploitation in the wild.

No official patch or fix is currently documented. Users should monitor the vendor's advisory channels for updates. Until a fix is released, restrict contributor-level access to trusted users only and consider disabling or removing the Simple Shopping Cart plugin if feasible. Avoid using the 'wp_cart_button' shortcode with untrusted input. Patch status is not yet confirmed — check the vendor advisory for current remediation guidance.