Summary
CVE-2026-11976 is a critical supply chain compromise affecting MonsterInsights Pro, a Google Analytics plugin for WordPress. Attackers breached the plugin’s official AWS S3 update distribution bucket and injected a malicious class-system-check.php file into releases 10.2.0 and 10.2.2, creating a covert backdoor (CWE-912: Hidden Functionality) that grants full remote control of affected sites. Severity is rated 10.0 (Critical).
Technical details
- Root cause: The official update distribution bucket (
monster-insights.s3.amazonaws.com) was compromised, allowing attackers to embed a maliciousclass-system-check.phpfile directly into legitimate plugin release packages. - Trigger conditions: Installing or updating to the backdoored MonsterInsights Pro 10.2.0 or 10.2.2 executes the injected code on the target WordPress site.
- Malware behavior: Multiple payload variants were identified, all sharing the same AES-256-GCM encryption key. The most severe variant hijacks the MonsterInsights and ExactMetrics update mechanisms and redirects future update checks to attacker infrastructure, creates a persistent backdoor WordPress administrator account, and implements an authentication bypass via a GET parameter. The backdoor persists even after the plugin is removed.
- Attack vector: Network — malicious code was distributed through compromised cloud infrastructure and executes server-side once installed.
- Impact: Full compromise of confidentiality, integrity, and availability, including persistent administrative access and attacker-controlled updates.
Affected software
- MonsterInsights Pro 10.2.0
- MonsterInsights Pro 10.2.2
Severity
- CVSS v3.1 base score: 10.0 (Critical)
- Vector:
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Mitigation and recommended actions
- Immediate: Update MonsterInsights Pro to version 11.0.0 or later, which is unaffected.
- If a compromised version was installed: Removing the plugin alone is insufficient, as the backdoor persists. Review all WordPress administrator accounts and remove any unauthorized entries, audit for unexpected update-check redirects to external infrastructure, and inspect for the injected
class-system-check.phpfile. Rotate credentials and rebuild from a known-clean state where compromise is confirmed.
How IONIX identifies potentially affected assets
IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.
- URL of a loaded script:
/wp-content/plugins/google-analytics-for-wordpress/….js

