CVE-2026-77186 describes a stored cross-site scripting vulnerability in the My Calendar – Accessible Event Manager plugin for WordPress. The issue exists in all versions up to and including 3.8.3 due to insufficient sanitization and escaping of the 'fallback' shortcode attribute. Attackers with contributor-level privileges can inject hex-encoded payloads that evade wp_kses_post filtering because they appear as literal backslash sequences. At render time, WordPress's shortcode_parse_atts() function decodes these sequences into actual HTML tags, resulting in execution of injected scripts in users' browsers.

Successful exploitation allows authenticated contributors or higher to inject persistent malicious scripts into pages, which execute in the context of users viewing those pages. This can lead to information disclosure, session hijacking, or other client-side impacts. The CVSS score of 6.4 reflects a medium severity with network attack vector, low attack complexity, and no user interaction required.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, restrict contributor-level access to trusted users only and consider disabling or limiting use of the 'fallback' shortcode attribute. Monitor vendor channels for an official patch or update.