What’s Vulnerable › Vulnerabilities

CVE-2026-40308: My Calendar: Unauthenticated Information Disclosure (IDOR) via Multisite switch_to_blog

• Severity: high (CVSS 8.8 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.9% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-04-16 · updated 2026-06-17
• Weakness: CWE-639

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.

Affected products

• joedolson my-calendar: before 3.7.7

References

• https://github.com/joedolson/my-calendar/releases/tag/v3.7.7
• https://github.com/joedolson/my-calendar/security/advisories/GHSA-2mvx-f5qm-v2ch
• https://github.com/joedolson/my-calendar/security/advisories/GHSA-2mvx-f5qm-v2ch

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