CVE-2026-11366 Overview
CVE-2026-11366 affects the MonsterInsights WordPress plugin in versions before 11.1.0. The plugin fails to correctly validate the HMAC signature on one of its unauthenticated AJAX actions. When the plugin is not connected to Google Analytics, the HMAC signing key remains empty. This condition allows unauthenticated attackers to forge a valid signature and overwrite a plugin configuration value. The impact disrupts server-side analytics in Manual GA4 mode. The issue is tracked under [CWE-287: Improper Authentication].
Critical Impact
Unauthenticated attackers can forge valid HMAC signatures against sites running MonsterInsights that are not connected to Google Analytics, overwriting configuration values and disrupting server-side analytics collection.
Affected Products
- MonsterInsights WordPress plugin versions prior to 11.1.0
- WordPress installations running MonsterInsights in Manual GA4 mode
- Sites where MonsterInsights is installed but not connected to Google Analytics
Discovery Timeline
- 2026-08-04 - CVE-2026-11366 published to NVD
- 2026-08-04 - Last updated in NVD database
Technical Details for CVE-2026-11366
Vulnerability Analysis
The vulnerability resides in an unauthenticated AJAX action exposed by the MonsterInsights plugin. The action relies on an HMAC signature to validate incoming requests. HMAC verification depends on a shared secret, which the plugin derives from its Google Analytics connection state.
When the plugin is not connected to Google Analytics, the HMAC signing key defaults to an empty string. An attacker who knows this state can compute a valid signature over any payload using the empty key. The AJAX handler then accepts the request as authentic and processes the attacker-supplied configuration overwrite. The EPSS score is 0.192% with a percentile of 9.097 as of 2026-08-06.
Root Cause
The root cause is a missing precondition check on the HMAC signing key. The plugin does not reject verification when the secret is empty or unset. Empty-key HMAC verification collapses signature authenticity, letting any attacker forge signed messages. This pattern maps directly to [CWE-287: Improper Authentication].
Attack Vector
Exploitation occurs over the network by sending a crafted POST request to the vulnerable WordPress AJAX endpoint. The attacker computes an HMAC using an empty key over the target payload and submits it as the signature parameter. No authentication or user interaction is required. The attack succeeds only on installations where MonsterInsights is not connected to Google Analytics, which raises attack complexity. Successful exploitation overwrites a plugin configuration value and disrupts Manual GA4 server-side analytics.
Refer to the WPScan Vulnerability Details for the technical writeup.
Detection Methods for CVE-2026-11366
Indicators of Compromise
- Unexpected changes to MonsterInsights plugin configuration options in the WordPress wp_options table
- POST requests to admin-ajax.php invoking MonsterInsights unauthenticated actions from unfamiliar IP addresses
- Sudden gaps or anomalies in Manual GA4 server-side analytics data
Detection Strategies
- Monitor web server access logs for anomalous unauthenticated POST traffic to wp-admin/admin-ajax.php referencing MonsterInsights actions
- Compare stored MonsterInsights configuration values against known-good baselines to detect unauthorized overwrites
- Alert on MonsterInsights plugin instances where the Google Analytics connection state is absent while AJAX actions are actively invoked
Monitoring Recommendations
- Enable WordPress audit logging to capture plugin option changes with source IP attribution
- Track version inventory of the MonsterInsights plugin across all managed WordPress sites and flag any version below 11.1.0
- Correlate analytics collection outages with recent AJAX activity to identify tampering events
How to Mitigate CVE-2026-11366
Immediate Actions Required
- Update the MonsterInsights WordPress plugin to version 11.1.0 or later on all WordPress installations
- Inventory WordPress sites to identify installations of MonsterInsights that are not yet connected to Google Analytics
- Review MonsterInsights configuration values for unauthorized modifications and restore known-good settings
Patch Information
Upgrade the MonsterInsights plugin to version 11.1.0 or later. The fixed release enforces proper HMAC signature validation and rejects verification attempts when the signing key is empty. See the WPScan Vulnerability Details for advisory information.
Workarounds
- Connect the MonsterInsights plugin to a Google Analytics account so the HMAC signing key is populated with a non-empty secret
- Deactivate the MonsterInsights plugin on sites where analytics is not required until the patch can be applied
- Restrict access to admin-ajax.php via a web application firewall rule that blocks unauthenticated invocations of MonsterInsights AJAX actions
# Example WP-CLI commands to identify and update vulnerable installations
wp plugin get google-analytics-for-wordpress --field=version
wp plugin update google-analytics-for-wordpress --version=11.1.0
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
