CVE-2026-57744: RT-Theme 18 Deserialization Vulnerability

CVE-2026-57744 Overview

CVE-2026-57744 is a PHP Object Injection vulnerability in the stmcan RT-Theme 18 Extensions plugin (rt18-extensions) for WordPress. The flaw stems from insecure deserialization of untrusted data [CWE-502] and affects all versions from initial release through 2.5. Unauthenticated attackers can submit crafted serialized payloads over the network to trigger object injection. Successful exploitation can lead to arbitrary code execution, data tampering, or full site compromise when a suitable gadget chain is present in the WordPress environment.

Critical Impact
Unauthenticated remote attackers can inject arbitrary PHP objects into the application, potentially leading to remote code execution and full compromise of the affected WordPress site.

Affected Products

stmcan RT-Theme 18 | Extensions (rt18-extensions) plugin for WordPress
All versions from initial release through 2.5
WordPress sites running the vulnerable plugin alongside classes containing exploitable magic methods

Discovery Timeline

2026-07-13 - CVE-2026-57744 published to NVD
2026-07-13 - Last updated in NVD database

Technical Details for CVE-2026-57744

Vulnerability Analysis

The vulnerability originates from the plugin passing attacker-controlled input to PHP's unserialize() function without validation. When PHP deserializes a crafted string, it instantiates arbitrary objects and invokes their magic methods such as __wakeup(), __destruct(), or __toString(). Attackers combine these methods across available classes to build a POP (Property-Oriented Programming) chain.

Because the plugin runs inside WordPress, gadget chains can leverage classes loaded by WordPress core, other plugins, or the theme itself. The result is code execution, arbitrary file operations, or SQL query manipulation depending on the available gadgets. No authentication is required, and no user interaction is needed for exploitation.

Root Cause

The root cause is the use of PHP deserialization on untrusted data received through the plugin's request handling. The plugin does not enforce integrity checks, signatures, or an allowlist of expected classes. Any serialized payload reaching the vulnerable sink is processed as trusted input.

Attack Vector

Exploitation occurs over the network against a public-facing WordPress endpoint exposed by the plugin. An attacker sends a crafted HTTP request containing a serialized PHP object string to a parameter that reaches unserialize(). Refer to the Patchstack advisory for the affected sink details.

// No verified public exploit code available.
// Vulnerability class: PHP Object Injection via unserialize() on attacker-controlled input.
// See Patchstack advisory for technical details.

Detection Methods for CVE-2026-57744

Indicators of Compromise

HTTP requests to rt18-extensions endpoints containing serialized PHP payloads matching patterns such as O: followed by a class name and length (for example, O:8:"stdClass").
Unexpected PHP processes spawned by the web server user, or new files written under wp-content/uploads/ shortly after suspicious requests.
WordPress admin users, options, or scheduled tasks created without a corresponding administrative session.

Detection Strategies

Inspect web server and WAF logs for request bodies or query parameters containing serialized object markers (O:, a:, s:) directed at plugin endpoints.
Monitor PHP error logs for __wakeup, __destruct, or class-not-found warnings that often accompany failed injection attempts.
Correlate anomalous outbound connections from the web server with recent POST requests to rt18-extensions handlers.

Monitoring Recommendations

Enable file integrity monitoring on WordPress core, themes, and plugin directories to catch webshell drops or plugin tampering.
Alert on new administrator accounts, changes to wp_options values such as active_plugins, and modifications to .htaccess.
Retain HTTP request bodies in access logs long enough to support retrospective hunts for object injection patterns.

How to Mitigate CVE-2026-57744

Immediate Actions Required

Update the RT-Theme 18 | Extensions plugin to a version later than 2.5 once the vendor publishes a fix.
If no patched version is available, deactivate and remove the rt18-extensions plugin from affected WordPress sites.
Rotate WordPress secret keys in wp-config.php, database credentials, and administrator passwords after confirming no compromise occurred.

Patch Information

At the time of publication, the vulnerability affects all versions through 2.5. Consult the Patchstack advisory for the latest fixed version and vendor guidance.

Workarounds

Deploy a Web Application Firewall rule that blocks request parameters containing PHP serialized object markers targeting the plugin's endpoints.
Restrict access to the affected plugin routes to trusted IP addresses using web server ACLs until a patched release is deployed.
Disable the plugin at the file system level by renaming its directory under wp-content/plugins/ if immediate removal via the admin UI is not possible.

bash

# Temporarily disable the vulnerable plugin from the shell
cd /var/www/html/wp-content/plugins/
mv rt18-extensions rt18-extensions.disabled