dbcve.org
Authorization Bypass (IDOR)Weakness · CWE-639

CVE-2026-40308

HIGH · 8.8 CVSS v4.0 Published 2026-04-16
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
97/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The My Calendar plugin's unauthenticated AJAX endpoint mc_ajax_mcjs_action uses parse_str() to process user-supplied arguments without validation, allowing injection of arbitrary parameters including a 'site' value. On Multisite installations, this enables unauthenticated switch_to_blog() calls to extract events from any sub-site. On Single Site installations, the non-existent switch_to_blog() function causes a fatal PHP error, creating a denial-of-service condition.

MitigationUpgrade My Calendar plugin to version 3.7.7 or later. As an interim measure, disable the plugin or restrict AJAX endpoints at the web server level until patching is possible.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
Authentication
X
User interaction
None
Scope
X

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify My Calendar plugin version
    Check the plugin header in my-calendar/my-calendar.php or view the installed version via WordPress admin plugins list
    Affected if version is below 3.7.7 (the patched release)
  2. Locate the vulnerable AJAX endpoint
    Verify the existence of the mc_ajax_mcjs_action handler by examining the plugin source code or testing access to /wp-admin/admin-ajax.php?action=mc_ajax_mcjs_action
    Affected if the endpoint exists and is registered without nonce or capability checks
  3. Confirm WordPress installation type
    Check wp-config.php for the definition of MULTISITE constant or the wp_blogs table existence in the database
    Affected if installation is Multisite (allows the switch_to_blog exploitation) or Single Site (causes fatal error on exploitation attempt)
  4. Verify parse_str usage in AJAX handler
    Search plugin source for mc_ajax_mcjs_action function and confirm it uses parse_str() on raw user input without sanitization
    Affected if parse_str() is called on $_GET or $_POST data without input validation

You are affected if My Calendar plugin version is below 3.7.7 AND the mc_ajax_mcjs_action AJAX endpoint is accessible on your WordPress installation.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade My Calendar plugin to version 3.7.7 or later. As an interim measure, disable the plugin or restrict AJAX endpoints at the web server level until patching is possible.

Recommended fix High confidence

My Calendar plugin version 3.7.7

  1. 1. Create a full backup of your WordPress site (database and files) before updating.
  2. 2. Navigate to Dashboard > Plugins in your WordPress admin area.
  3. 3. Locate the 'My Calendar' plugin in your installed plugins list.
  4. 4. If an update is available, click 'Update Now' to update to version 3.7.7.
  5. 5. Alternatively, download My Calendar version 3.7.7 from the WordPress Plugin Repository or the developer's GitHub and upload via Plugins > Add New > Upload Plugin.
  6. 6. After updating, verify the plugin is running version 3.7.7 by checking the plugins list.
  7. 7. Test that calendar functionality works correctly on your site.
Caveat No breaking changes documented for this security update

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing5.0 h
  • Review / QA3.0 h
17.0 hours of engineering $2,970
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-40308 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data