The proxymis HTML5 Chat plugin for WordPress suffers from a stored cross-site scripting vulnerability (CWE-79) due to improper neutralization of input during web page generation. Specifically, the plugin's 'HTML5CHAT' shortcode does not sufficiently sanitize or escape user-supplied attributes, allowing authenticated users with contributor or higher privileges to inject malicious scripts. These scripts execute in the context of any user who accesses the injected page, potentially leading to session hijacking or other script-based attacks. The vulnerability affects all versions up to 1.07. The CVSS 3.1 base score is 6.4, reflecting network attack vector, low attack complexity, privileges required, no user interaction, and partial confidentiality and integrity impact. No patch or vendor advisory is currently available to confirm remediation status.

An attacker with contributor-level or higher access can inject persistent malicious scripts into pages via the vulnerable shortcode. These scripts execute in the browsers of users who view the infected pages, potentially compromising user sessions or data confidentiality and integrity. The vulnerability does not impact availability. There are no known exploits in the wild, but the risk remains for sites using affected plugin versions without mitigation.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is released, site administrators should restrict contributor-level access, disable or remove the HTML5 Chat plugin, or implement manual input sanitization and output escaping controls if feasible. Monitoring for unusual script injections in content may help detect exploitation attempts.