VulnerabilityDeferred

CVE-2026-40308

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.

HIGH 8.8EPSS 0.93%

Does this matter?

High impact if exploited, but EPSS currently rates exploitation as unlikely (0.93%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.

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.

CVSS 4.0: 8.8 HIGHCVSS: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/M
EPSS: 0.93% probability · 59th percentile
CISA KEV: Not listed
Weakness: CWE-639
Source: security-advisories@github.com

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.