CVE-2026-0726: Nexter WordPress Plugin RCE Vulnerability

CVE-2026-0726 Overview

The Nexter Extension – Site Enhancements Toolkit plugin for WordPress contains a PHP Object Injection vulnerability in all versions up to and including 4.4.6. The vulnerability exists due to improper deserialization of untrusted input in the nxt_unserialize_replace function, allowing unauthenticated attackers to inject malicious PHP objects into the application.

Critical Impact

Unauthenticated attackers can exploit this vulnerability to inject PHP objects. When combined with a Property Oriented Programming (POP) chain from another installed plugin or theme, attackers may delete arbitrary files, retrieve sensitive data, or execute arbitrary code on the target system.

Affected Products

• Nexter Extension – Site Enhancements Toolkit plugin for WordPress versions up to and including 4.4.6
• WordPress installations with the vulnerable Nexter Extension plugin
• Systems with additional plugins or themes containing exploitable POP chains

Discovery Timeline

• 2026-01-20 - CVE-2026-0726 published to NVD
• 2026-01-20 - Last updated in NVD database

Technical Details for CVE-2026-0726

Vulnerability Analysis

This vulnerability is classified as CWE-502 (Deserialization of Untrusted Data), a common weakness in PHP applications that handle serialized data without proper validation. The vulnerability resides in the nxt_unserialize_replace function within the nexter-ext-replace-url.php file, which processes user-supplied serialized data without adequate security controls.

PHP Object Injection occurs when an application deserializes untrusted data, allowing attackers to control the properties of instantiated objects. While the Nexter Extension plugin itself does not contain a known POP (Property Oriented Programming) chain, the injection of crafted PHP objects becomes dangerous when combined with other WordPress components that do contain exploitable chains.

The attack requires no authentication, meaning any remote attacker with network access to the WordPress site can attempt exploitation. The potential impact depends entirely on the presence of exploitable POP chains in other installed plugins or themes on the target system.

Root Cause

The root cause of this vulnerability is the use of PHP's unserialize() function on untrusted input within the nxt_unserialize_replace function. The application fails to validate or sanitize the serialized data before deserialization, allowing arbitrary PHP objects to be instantiated with attacker-controlled properties. Secure alternatives such as json_encode()/json_decode() or implementing strict type checking before deserialization were not employed.

Attack Vector

The vulnerability is exploitable over the network without requiring user interaction or authentication. An attacker crafts a malicious serialized PHP object payload and sends it to the vulnerable endpoint. When the nxt_unserialize_replace function processes this payload, the malicious object is instantiated. If a compatible POP chain exists in another installed component, the attacker can chain object method calls to achieve various malicious outcomes including:

• Arbitrary file deletion leading to site compromise or denial of service
• Sensitive data exfiltration including database credentials
• Remote code execution through file manipulation or direct code evaluation

The exploitation mechanism relies on PHP's magic methods (such as __wakeup(), __destruct(), or __toString()) being triggered during or after unserialization, which then execute attacker-controlled actions through the POP chain.

Detection Methods for CVE-2026-0726

Indicators of Compromise

• Unusual serialized data patterns in HTTP request logs, particularly containing PHP object notation (e.g., O: prefixes followed by class names)
• Web server logs showing requests to plugin endpoints with large or malformed payloads
• Unexpected file modifications or deletions in the WordPress installation directory
• Anomalous PHP process execution or memory usage patterns

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block serialized PHP object patterns in incoming requests
• Monitor application logs for deserialization errors or unusual object instantiation
• Deploy file integrity monitoring to detect unauthorized changes to WordPress files
• Use SentinelOne Singularity XDR to detect post-exploitation behaviors such as unauthorized file access or code execution

Monitoring Recommendations

• Enable verbose logging for the Nexter Extension plugin and review logs for suspicious activity
• Configure alerts for failed authentication attempts followed by plugin endpoint access
• Monitor outbound network connections from the WordPress server for potential data exfiltration
• Implement real-time monitoring of critical WordPress directories for unexpected modifications

How to Mitigate CVE-2026-0726

Immediate Actions Required

• Update the Nexter Extension plugin to version 4.4.7 or later immediately
• Audit installed plugins and themes for known POP chains that could be leveraged in conjunction with this vulnerability
• Review web server logs for any suspicious serialized data submissions
• Consider temporarily disabling the Nexter Extension plugin until patching is complete

Patch Information

The vulnerability has been addressed in Nexter Extension version 4.4.7. The fix can be reviewed in the WordPress Changeset Update. Additional technical details are available in the Wordfence Vulnerability Report.

Workarounds

• If immediate patching is not possible, disable the Nexter Extension plugin until the update can be applied
• Implement WAF rules to block requests containing serialized PHP object patterns targeting plugin endpoints
• Restrict access to WordPress admin and plugin endpoints using IP allowlisting
• Remove unnecessary plugins and themes to reduce the attack surface and potential POP chain availability

# Configuration example - Disable plugin via WP-CLI
wp plugin deactivate nexter-extension

# Update plugin to patched version
wp plugin update nexter-extension --version=4.4.7

# Verify plugin version after update
wp plugin get nexter-extension --field=version