What’s Vulnerable › Vulnerabilities

CVE-2026-104798: My Calendar <= 3.8.7 - Unauthenticated Privilege Escalation to 'mcs' Parameter via Reflected Shortcode Injection into 'above' Attribute

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-16 · updated 2026-10-16
• Weakness: CWE-269

Description

The My Calendar – Accessible Event Manager plugin for WordPress is vulnerable to Privilege Escalation in all versions up to, and including, 3.8.7. The public `mcs` GET parameter is reflected into post content unsanitized before WordPress core's `do_shortcode` filter runs, allowing an unauthenticated attacker to inject a nested `[my_calendar above=...]` shortcode; `mc_generate_calendar_nav()` then splits the `above` attribute on commas and dispatches each element via `call_user_func()` with no authentication, authorization, or callable allowlist check. This makes it possible for unauthenticated attackers to invoke arbitrary loaded PHP functions, enabling a call chain in which the shortcode `$params` array is passed to `edit_user()` — which PHP coerces to integer `1` as the `$user_id` argument — overwriting the credentials of the initial Administrator account (user ID 1) and granting the attacker full wp-admin access. Exploitation is trivially reachable via the plugin's auto-generated `/my-calendar/` page, which is publicly accessible by default upon plugin activation.

Affected products

• joedolson My Calendar – Accessible Event Manager: through 3.4.24; from 3.5 through 3.5.21; from 3.6 through 3.6.17; from 3.7 through 3.7.17; from 3.8 through 3.8.7

References

• https://plugins.trac.wordpress.org/browser/my-calendar/tags/3.8.6/my-calendar-navigation.php#L248
• https://plugins.trac.wordpress.org/browser/my-calendar/tags/3.8.6/my-calendar-navigation.php#L260
• https://plugins.trac.wordpress.org/browser/my-calendar/tags/3.8.6/my-calendar-output.php#L1622
• https://plugins.trac.wordpress.org/browser/my-calendar/tags/3.8.6/my-calendar-search.php#L170
• https://plugins.trac.wordpress.org/browser/my-calendar/tags/3.8.6/my-calendar-search.php#L221
• https://plugins.trac.wordpress.org/browser/my-calendar/tags/3.8.6/my-calendar-shortcodes.php#L102
• https://plugins.trac.wordpress.org/changeset?reponame=&old=3746389%40my-calendar&new=3746389%40my-calendar
• https://www.wordfence.com/threat-intel/vulnerabilities/id/e8aa6ee7-525e-4458-9f5b-1e729afe448c?source=cve

Get alerted when CVE-2026-104798 or the next vulnerability affects your stack