CVE-2026-40308: My Calendar is a WordPress plugin for managing calendar events. In versions 3.7.6 and below, the mc_ajax_mcjs_action AJAX endpoint, registered for una...

Description

My Calendar is a WordPress plugin for managing calendar events. In versions 3.7.6 and below, the mc_ajax_mcjs_action AJAX endpoint, registered for unauthenticated users, passes user-supplied arguments through parse_str() without validation, allowing injection of arbitrary parameters including a site value. On WordPress Multisite installations, this enables an unauthenticated attacker to call switch_to_blog() with an arbitrary site ID and extract calendar events from any sub-site on the network, including private or hidden events. On standard Single Site installations, switch_to_blog() does not exist, causing an uncaught PHP fatal error and crashing the worker thread, creating an unauthenticated denial of service vector. This issue has been fixed in version 3.7.7.

Metrics

CVSS 4.0

8.8/10

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability

0.93%

56.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-639

References

Timeline

Published: Apr 16, 2026
Last Modified: Jun 17, 2026
Status: Deferred

Frequently Asked Questions

What is CVE-2026-40308?

My Calendar is a WordPress plugin for managing calendar events. In versions 3.7.6 and below, the mc_ajax_mcjs_action AJAX endpoint, registered for unauthenticated users, passes user-supplied arguments through parse_str() without validation, allowing injection of arbitrary parameters including a site value. On WordPress Multisite installations, this enables an unauthenticated attacker to call switch_to_blog() with an arbitrary site ID and extract calendar events from any sub-site on the network, including private or hidden events. On standard Single Site installations, switch_to_blog() does not exist, causing an uncaught PHP fatal error and crashing the worker thread, creating an unauthenticated denial of service vector. This issue has been fixed in version 3.7.7.

How severe is CVE-2026-40308?

CVE-2026-40308 has a CVSS score of 8.8/10 (HIGH severity). The EPSS model estimates a 0.93% probability of exploitation in the next 30 days.

How do I fix CVE-2026-40308?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.