My Calendar Stored Cross-Site Scripting Vulnerability via Shortcode Attributes

A stored cross-site scripting vulnerability has been identified in the My Calendar – Accessible Event Manager plugin for WordPress, affecting all versions through 3.7.3. The issue arises in the 'mc_draw_template()' function, where user-supplied shortcode attribute values are improperly sanitized. The 'template' attribute of the '[my_calendar_upcoming]' shortcode can be exploited by authenticated attackers with Contributor-level access and above, allowing them to inject arbitrary scripts that execute when a user views the affected page.

Impact

Exploitation of this vulnerability allows for stored cross-site scripting, where injected scripts are executed in the context of the user viewing the page.

Reproduction

To reproduce this vulnerability, an authenticated user with Contributor-level access or higher can use the '[my_calendar_upcoming]' shortcode and include a crafted 'template' attribute that contains JavaScript code. The 'stripcslashes()' function will decode the injected script, bypassing WordPress's normal content sanitization, and the script will be executed when the page is viewed.

Remediation

Users are advised to update the My Calendar – Accessible Event Manager plugin to version 3.7.4 or later.