CVE-2026-2471: WP Mail Logging Plugin RCE Vulnerability

CVE-2026-2471 Overview

The WP Mail Logging plugin for WordPress is vulnerable to PHP Object Injection in all versions up to, and including, 1.15.0 via deserialization of untrusted input from the email log message field. This insecure deserialization vulnerability (CWE-502) occurs because the BaseModel class constructor calls maybe_unserialize() on all properties retrieved from the database without proper validation. Unauthenticated attackers can inject a PHP Object by submitting a double-serialized payload through any public-facing form that sends email, such as Contact Form 7.

Critical Impact

When a malicious email is logged and subsequently viewed by an administrator, the payload is deserialized into an arbitrary PHP object. If a POP (Property-Oriented Programming) chain exists via another plugin or theme, attackers may delete arbitrary files, retrieve sensitive data, or achieve remote code execution.

Affected Products

• WP Mail Logging plugin for WordPress versions up to and including 1.15.0
• WordPress installations using vulnerable versions of WP Mail Logging with public-facing contact forms
• Sites with additional plugins or themes containing POP chains are at elevated risk

Discovery Timeline

• February 28, 2026 - CVE-2026-2471 published to NVD
• March 2, 2026 - Last updated in NVD database

Technical Details for CVE-2026-2471

Vulnerability Analysis

This PHP Object Injection vulnerability exists due to unsafe deserialization practices in the WP Mail Logging plugin's ORM layer. The BaseModel class, which serves as the foundation for data model handling, indiscriminately calls maybe_unserialize() on all properties retrieved from the database. This function automatically unserializes data when it detects serialized strings, creating a dangerous pathway for object injection attacks.

The attack requires no authentication, as the malicious payload can be delivered through any public-facing form that triggers email functionality (such as Contact Form 7). When a user submits a form containing a double-serialized malicious payload, the email content including the payload is stored in the database. The vulnerability is triggered when an administrator views the email log, causing the BaseModel to deserialize the stored payload.

While no native POP chain exists within the WP Mail Logging plugin itself, WordPress sites commonly run multiple plugins and themes. If any installed component contains a suitable POP chain, the deserialized object can be leveraged to perform dangerous operations including file deletion, data exfiltration, or arbitrary code execution.

Root Cause

The root cause lies in the BaseModel class constructor at line 39 of BaseModel.php, where the plugin calls maybe_unserialize() on database-retrieved properties without validating the source or sanitizing the input. This pattern of trusting serialized data from user-controllable fields violates secure coding principles for handling untrusted input. The double-serialization technique allows attackers to bypass initial unserialize operations and have their payload processed when the log entry is rendered.

Attack Vector

The attack leverages a network-based vector requiring no privileges but necessitating user interaction (an administrator must view the logged email). An attacker crafts a double-serialized PHP object payload and submits it through a public contact form. The payload traverses through the email logging system and is stored in the database. When an administrator accesses the mail log through the WordPress admin panel, the WPML_MailRenderer_AJAX_Handler processes the log entry, triggering deserialization of the malicious object.

The double-serialization technique works because the first layer of serialization is stripped when the email is initially processed and stored, leaving the inner serialized object intact. Upon retrieval and rendering, the maybe_unserialize() call in BaseModel processes the remaining serialized data, instantiating the attacker-controlled object.

Detection Methods for CVE-2026-2471

Indicators of Compromise

• Presence of serialized PHP object patterns in email log database entries, particularly containing class names from other installed plugins or themes
• Unusual O: (object) or a: (array) serialization markers within email body fields in the wp_mail_logging database table
• Unexpected file modifications or deletions on the WordPress installation following administrator access to mail logs
• Error logs showing PHP unserialization warnings or object instantiation failures

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block serialized PHP object patterns in form submissions
• Monitor database queries for suspicious serialized content being written to mail logging tables
• Deploy file integrity monitoring to detect unauthorized file changes that may result from successful exploitation
• Review PHP error logs for deserialization-related warnings or notices

Monitoring Recommendations

• Enable detailed logging on WordPress admin actions, particularly around the mail logging interface
• Configure SIEM alerts for patterns matching PHP serialized objects in HTTP POST data
• Monitor for unusual administrative activity patterns following form submissions
• Implement real-time alerting for any changes to critical WordPress files or database tables

How to Mitigate CVE-2026-2471

Immediate Actions Required

• Update WP Mail Logging plugin to a version newer than 1.15.0 immediately
• Audit your WordPress installation for additional plugins or themes that may contain POP chains
• Review recent email logs for suspicious serialized content before the update is applied
• Consider temporarily disabling the WP Mail Logging plugin until the patch is applied if immediate updating is not possible

Patch Information

The vulnerability has been addressed in versions after 1.15.0. The WordPress Plugin ChangeSet Details contains the specific code changes implementing the fix. Additional technical analysis is available from the Wordfence Vulnerability Analysis.

Workarounds

• Disable the WP Mail Logging plugin entirely until an update can be applied
• Restrict administrative access to the mail logs section to minimize the chance of triggering deserialization
• Implement server-side input filtering to strip or neutralize serialized PHP object patterns in form submissions
• Remove unnecessary plugins and themes that may contain POP chains to reduce the attack surface

# Disable WP Mail Logging plugin via WP-CLI until patched
wp plugin deactivate wp-mail-logging

# Verify current plugin version
wp plugin get wp-mail-logging --field=version

# Update to patched version when available
wp plugin update wp-mail-logging