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My Calendar <= 3.8.7 — Unauthenticated Privilege Escalation to 'mcs' Parameter via Reflected Shortcode Injection into 'above' Attribute

CVE-2026-104798Published · Updated

Action summary

Affected: ≤3.8.7Update to 3.4.25 or 3.5.22 or 3.6.18 or 3.7.18 or 3.8.8 or newer

Fixed versions are per release branch: update to the fix for the branch you run.

All remediation steps
Watch plugin
Severity
Critical9.8
CVSS
9.8
CVSS 3.1 · CNA (Wordfence)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
What does this vector mean?
AV:N Attack vector
Network
AC:L Attack complexity
Low
PR:N Privileges required
None
UI:N User interaction
None
S:U Scope
Unchanged
C:H Confidentiality
High
I:H Integrity
High
A:H Availability
High
Weakness
CWE-269 Privilege Escalation
Required access
No account needed
Exploit prediction (EPSS)
0.5% chance in 30 days41th percentile
CISA KEV
Not listed
On this page8

Am I affected?

My Calendar – Accessible Event Manager my-calendar

  1. Affected≤ 3.8.7
  2. Patched in3.4.25 / 3.5.22 / 3.6.18 / 3.7.18 / 3.8.8

Update to 3.4.25 / 3.5.22 / 3.6.18 / 3.7.18 / 3.8.8 or newer.

You are affected if you run ≤ 3.8.7. Version 3.4.25, 3.5.22, 3.6.18, 3.7.18, 3.8.8 and later are not affected by this issue.

  • Check your version: in wp-admin go to Plugins → Installed Plugins and read the version under My Calendar – Accessible Event Manager.
  • No admin access? Run a passive check of your site. It reads public files only.
  • No account is needed to exploit this. Treat any exposed site on an affected version as at risk.

What to do

  1. Update to one of the following versions, or a newer patched version: 3.4.25, 3.5.22, 3.6.18, 3.7.18, 3.8.8
  2. Rotate administrator passwords and application secrets if the site ran a vulnerable version while publicly reachable.
  3. Watch My Calendar – Accessible Event Manager to get an email when the next vulnerability is published.

Advisory

Source description from Wordfence Intelligence, credited to daroo.

The My Calendar – Accessible Event Manager plugin for WordPress is vulnerable to Privilege Escalation in all versions up to, and including, 3.8.7. The public `mcs` GET parameter is reflected into post content unsanitized before WordPress core's `do_shortcode` filter runs, allowing an unauthenticated attacker to inject a nested `[my_calendar above=...]` shortcode; `mc_generate_calendar_nav()` then splits the `above` attribute on commas and dispatches each element via `call_user_func()` with no authentication, authorization, or callable allowlist check. This makes it possible for unauthenticated attackers to invoke arbitrary loaded PHP functions, enabling a call chain in which the shortcode `$params` array is passed to `edit_user()` — which PHP coerces to integer `1` as the `$user_id` argument — overwriting the credentials of the initial Administrator account (user ID 1) and granting the attacker full wp-admin access. Exploitation is trivially reachable via the plugin's auto-generated `/my-calendar/` page, which is publicly accessible by default upon plugin activation.

Exploits & references

Proof-of-concept & detection

No public proof-of-concept or detection template is known for this vulnerability.

Advisories & patches

More in My Calendar – Accessible Event Manager

All 24
More vulnerabilities in My Calendar – Accessible Event Manager
SeverityVulnerabilityCVEPublished
Medium6.53.8.11 - Unauthenticated Arbitrary Shortcode Execution
3.8.8 – <3.8.11Update to 3.8.11
CVE-2026-119714
Medium6.4Authenticated (Contributor+) Stored Cross-Site Scripting via 'fallback' Shortcode Attribute
≤3.8.3Update to 3.8.4
CVE-2026-77186
Medium6.4Authenticated (Contributor+) Stored Cross-Site Scripting via 'before' and 'after' Shortcode Attributes
≤3.8.3Update to 3.8.4
CVE-2026-77187
High7.5Unauthenticated SQL Injection via 'mc_auth' and 'mc_host' Parameters
≤3.7.8Update to 3.7.9
CVE-2026-6854
Medium5.3Insecure Direct Object Reference to Unauthenticated Sensitive Information Disclosure via 'vcal' Parameter
≤3.7.14Update to 3.7.15
CVE-2026-11896

Same weakness (Privilege Escalation)

All Privilege Escalation
Other Privilege Escalation vulnerabilities
SeverityVulnerabilityCVEPublished
High7.2Unauthenticated Stored Cross-Site Scripting via Comment User-Agent Header
EZ SQL Reports Shortcode Widget and DB Backup≤5.25.25Update to 5.26.45
CVE-2026-120688
Critical9.8Unauthenticated Arbitrary File Upload via File Upload via Public Form Submission
Chatterbug Forms – Fast, Flexible WordPress Form Builder≤1.0.2Update to 1.1
CVE-2026-125055
Critical9.8Unauthenticated PHP Object Injection to Remote Code Execution via 'form' Parameter
ELEX WordPress HelpDesk & Customer Ticketing System≤3.3.9Update to 3.4.0
CVE-2026-119077
Medium5.3Unauthenticated Sensitive Information Exposure in 'search' Parameter
Customer Reviews for WooCommerce≤5.127.0Update to 5.128.0
CVE-2026-121518

Timeline

  1. CVE published

    Severity critical, CVSS 9.8

  2. Record last updated

Sources & licenses

Wordfence record
Vulnerability data
Wordfence Intelligence. Copyright 2012-2026 Defiant Inc. Licensed under the CC BY-SA 4.0.
CVE® identifiers
Copyright 1999-2026 The MITRE Corporation. Used under the CVE Program. CVE® is a registered trademark of The MITRE Corporation.
CVSS / CWE
National Vulnerability Database (NVD), shown unmodified. This product uses the NVD API but is not endorsed or certified by the NVD.
EPSS
Exploit Prediction Scoring System by FIRST.org.
VulnCrest content
Summary, remediation guidance and page layout © VulnCrest. Not sourced from NVD.

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