CVE-2026-39474: Post Duplicator PHP Object Injection Flaw

CVE-2026-39474 Overview

CVE-2026-39474 is a PHP Object Injection vulnerability affecting the Post Duplicator WordPress plugin in versions up to and including 3.0.10. The flaw allows authenticated users holding Contributor-level privileges to inject crafted PHP serialized objects into the application. Successful exploitation can result in arbitrary code execution, data tampering, or denial of service depending on the gadget chains available in the WordPress instance. The vulnerability is tracked under CWE-502: Deserialization of Untrusted Data.

Critical Impact
Authenticated Contributor accounts can trigger PHP Object Injection to compromise confidentiality, integrity, and availability of WordPress sites running Post Duplicator 3.0.10 or earlier.

Affected Products

Post Duplicator WordPress plugin versions <= 3.0.10
WordPress installations with the plugin active
Sites permitting Contributor or higher role accounts

Discovery Timeline

2026-06-15 - CVE-2026-39474 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2026-39474

Vulnerability Analysis

The Post Duplicator plugin processes user-supplied input through PHP's unserialize() function without enforcing safe class restrictions. When a Contributor submits crafted serialized data, the plugin instantiates arbitrary PHP objects within the WordPress runtime. Object instantiation triggers magic methods such as __wakeup() and __destruct(), which can chain into existing classes loaded by WordPress core, themes, or other plugins. The result is a classic POP (Property-Oriented Programming) chain attack surface mapped to [CWE-502].

Exploitation requires only Contributor-level authentication, a role widely granted to guest authors and editorial staff on multi-author WordPress sites. The attack is delivered over the network through standard HTTP requests to the plugin's duplication endpoints. Because gadget chains depend on the surrounding plugin ecosystem, impact scales with the complexity of the target site.

Root Cause

The root cause is unsafe deserialization of attacker-controlled input. The plugin fails to validate or sanitize serialized payloads before passing them to PHP's deserialization routines, violating secure coding guidance to either avoid unserialize() on untrusted data or use allowed_classes constraints.

Attack Vector

An authenticated attacker with Contributor privileges submits a serialized PHP object via a plugin parameter handled during post duplication. The crafted object exploits gadget chains in loaded PHP classes to execute attacker-defined logic. Refer to the Patchstack advisory for technical details on the affected code paths. No public proof-of-concept exploit has been published at the time of writing.

Detection Methods for CVE-2026-39474

Indicators of Compromise

Unexpected outbound network connections originating from the PHP-FPM or web server process tied to Post Duplicator request flows.
New or modified PHP files under wp-content/uploads/ or wp-content/plugins/ shortly after duplication requests from Contributor accounts.
WordPress access logs showing POST requests to Post Duplicator endpoints containing serialized payloads beginning with O: or a:.

Detection Strategies

Inspect HTTP request bodies and query parameters destined for Post Duplicator routes for serialized PHP signatures such as O:8: and s: length-prefixed strings.
Monitor WordPress audit logs for Contributor accounts invoking duplication actions outside normal editorial workflows.
Correlate web server process spawns of sh, bash, php, or curl immediately following plugin requests.

Monitoring Recommendations

Enable verbose logging on the WordPress instance and forward logs to a centralized SIEM for [CWE-502] pattern matching.
Alert on creation of new administrator accounts or modifications to wp_options directly after Post Duplicator activity.
Track file integrity on the plugin directory and document root using checksum baselines.

How to Mitigate CVE-2026-39474

Immediate Actions Required

Update the Post Duplicator plugin to a version newer than 3.0.10 as soon as a fixed release is available from the vendor.
Audit all Contributor and higher-privilege accounts and remove inactive or unverified users.
Disable the Post Duplicator plugin if a patched version cannot be deployed immediately.

Patch Information

Review the Patchstack vulnerability database entry for the current patch status and recommended upgrade target. Apply the fixed plugin version through the WordPress admin dashboard or by replacing plugin files via SFTP.

Workarounds

Restrict Contributor role assignments and require manual editorial approval before granting access.
Deploy a Web Application Firewall (WAF) rule that blocks serialized PHP payloads in requests targeting the plugin's endpoints.
Apply virtual patching through Patchstack or an equivalent WordPress security service until the official fix is installed.

bash

# Example WAF rule blocking serialized PHP payloads to Post Duplicator endpoints
SecRule REQUEST_URI "@contains /wp-admin/admin.php" \
  "chain,deny,status:403,id:1039474,msg:'CVE-2026-39474 PHP Object Injection attempt'"
SecRule ARGS "@rx O:[0-9]+:\"[A-Za-z_][A-Za-z0-9_]*\":[0-9]+:" \
  "t:none"