Unauthenticated Information Disclosure (IDOR) via Multisite switch_to_blog in My Calendar

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.8 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-40308: 0.93% estimated exploitation activity in the next 30 days; percentile 60.73 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary An unauthenticated Insecure Direct Object Reference (IDOR) and Denial of Service (DoS) vulnerability in the My Calendar plugin allows any unauthenticated user to extract calendar events (including private or hidden ones) from any sub-site on a WordPress Multisite network. On standard Single Site WordPress installations, this same endpoint crashes the PHP worker thread, creating an unauthenticated Denial of Service (DoS) vector. Details The vulnerability stems from the mcajaxmcjsaction AJAX function, which handles the mcjsaction endpoint. This endpoint is explicitly registered for unauthenticated users: When the behavior parameter is set to loadupcoming, the plugin accepts an args parameter from the $REQUEST array. Instead of validating specific expected arguments, the plugin unsafely passes the entire string into PHP's parsestr() function: This allows an attacker to inject arbitrary key-value pairs into the $args array. This array is then passed to the…

Published by the source

16 Apr 2026, 21:34 UTC

Last modified by the source

16 Apr 2026, 21:34 UTC

Source last checked

26 Oct 2026, 14:39 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-2mvx-f5qm-v2ch

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# Patch Next advisory brief: CVE-2026-40308

Advisory: Unauthenticated Information Disclosure (IDOR) via Multisite switch_to_blog in My Calendar
IDs: CVE-2026-40308, GHSA-2mvx-f5qm-v2ch
Record: https://patchnext.com/advisories/cve-2026-40308 (revision 1, source checked 26 Oct 2026, 14:39 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: joedolson/my-calendar 3.7.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist joedolson/my-calendar: affected < 3.7.7; fixed in 3.7.7

## Suggested inspection (read-only)
- Packagist joedolson/my-calendar: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on joedolson/my-calendar.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-2mvx-f5qm-v2ch (GitHub-reviewed advisory GHSA-2mvx-f5qm-v2ch lists affected ranges: Packagist joedolson/my-calendar >=0 <3.7.7)

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