WordPress ARForms Plugin Critical PHP Object Injection — CVE-2024-13784

Executive Summary

A critical unauthenticated PHP object injection vulnerability has been disclosed in the ARForms – Contact Form, Survey, Quiz & Popup Form Builder WordPress plugin by ReputeInfoSystems. Tracked as CVE-2024-13784 (CVSS 9.8), the flaw allows any remote attacker without authentication to inject arbitrary PHP objects through the plugin's deserialization of untrusted form input. Successful exploitation — depending on the presence of a Property-Oriented Programming (POP) chain from a co-installed plugin or theme — can lead to arbitrary code execution, file deletion, or sensitive data disclosure.

Vulnerability Details

Technical Analysis

The vulnerability resides in ARForms' handling of submitted form data. The plugin passes user-supplied input directly to PHP's unserialize() function without adequate sanitization or validation. An attacker can craft a malicious serialized PHP object payload embedded in a form submission and send it to any site running the vulnerable plugin.

Exploitation Requirements

Exploitation requires a POP (Property-Oriented Programming) chain to be present in the WordPress environment — typically through another installed plugin or theme. The ARForms plugin itself does not ship a usable POP chain. However, given the vast WordPress plugin ecosystem, many sites will have co-installed components that introduce exploitable chains. When a suitable chain exists, an attacker can leverage object injection to:

• Execute arbitrary PHP code on the server
• Delete arbitrary files, potentially destroying the WordPress installation
• Retrieve sensitive data including credentials, API keys, and private content

Attack Vector

The attack is fully network-accessible with:

• No authentication required
• No prior knowledge of the site
• No user interaction needed
• Low attack complexity

This places the vulnerability among the most dangerous classes of WordPress plugin flaws.

Affected Software

Mitigation

No official patch has been released as of this advisory. Administrators running ARForms should take immediate defensive action:

1. Disable the ARForms plugin temporarily if it is not business-critical, until a patched version is released.
2. Audit co-installed plugins and themes for known POP chains — tools like Wordfence and Patchstack can assist with this.
3. Deploy a Web Application Firewall (WAF) configured to block PHP serialization payloads (O:<length>:"ClassName" patterns) at the HTTP layer.
4. Monitor vendor advisory channels — watch the ARForms plugin page on WordPress.org, Wordfence, and Patchstack for an updated release.
5. Limit form submission exposure — ensure the plugin's form endpoints are not exposed to unauthenticated traffic if possible.

Detection

Look for suspicious POST requests containing PHP serialized object patterns in web server logs. Indicators include:

• Request bodies containing O:<number>: patterns characteristic of PHP object serialization
• Unusual POST payloads targeting ARForms endpoints
• Unexpected file creation or deletion events following form submissions

References

• Wordfence Advisory
• NVD — CVE-2024-13784
• ARForms Plugin — WordPress.org