The My Calendar – Accessible Event Manager plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the template attribute of the [my_calendar_upcoming] shortcode in all versions up to, and including, 3.7.3. This is due to the use of stripcslashes() on user-supplied shortcode attribute values in the mc_draw_template() function, which decodes C-style hex escape sequences (e.g., \x3c to <) at render time, bypassing WordPress's wp_kses_post() content sanitization that runs at save time. This makes it possible for authenticated attackers, with Contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.