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

> Unauthenticated attackers can extract private calendar events from any sub-site on WordPress Multisite installations or cause denial of service on single-site installations.

- **Severity:** High 8.8 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Apr 2026
- **Updated:** 17 Apr 2026
- **Also known as:** GHSA-2mvx-f5qm-v2ch

## What is CVE-2026-40308?

CVE-2026-40308 is a high-severity vulnerability in joedolson my-calendar, published on 16 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-639 (Authorization Bypass Through User-Controlled Key)

## Which versions are affected by CVE-2026-40308?

2 open source packages ship an affected version, including joedolson/my-calendar.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `joedolson/my-calendar` | Packagist | All versions | 3.7.7 |
| `joedolson/my-calendar` | Packagist | All versions | 3.7.7 |

## How do I fix CVE-2026-40308?

Upgrade joedolson/my-calendar to 3.7.7 or later.

## Is CVE-2026-40308 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40308 exists.

Public exploit code:

- My Calendar WordPress Plugin - Information Disclosure (nuclei): http/cves/2026/CVE-2026-40308.yaml

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40308 and fix it if it is affected.

What it is: CVE-2026-40308 is a high-severity vulnerability in joedolson my-calendar, published on 16 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40308 exists.

Affected packages and fixed versions:
- joedolson/my-calendar (Packagist): affected all versions; fixed in 3.7.7
- joedolson/my-calendar (Packagist): affected all versions; fixed in 3.7.7

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-40308/ (Markdown: https://insights.sbomify.com/CVE-2026-40308/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40308
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40308
- OSV: https://osv.dev/vulnerability/CVE-2026-40308

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40308/
Summaries are generated and may contain mistakes; the official description above is the record.