CVE-2023-28782: Gravity Forms Deserialization Vulnerability

CVE-2023-28782 Overview

CVE-2023-28782 is a critical deserialization of untrusted data vulnerability (CWE-502) affecting Gravity Forms, a popular WordPress form plugin developed by Rocketgenius Inc. This vulnerability allows unauthenticated attackers to exploit PHP Object Injection through the deserialization of untrusted data, potentially leading to remote code execution, data theft, or complete site compromise.

Critical Impact

Unauthenticated attackers can exploit this PHP Object Injection vulnerability to execute arbitrary code, access sensitive data, or take complete control of affected WordPress installations running vulnerable versions of Gravity Forms.

Affected Products

• Gravity Forms plugin for WordPress versions through 2.7.3
• WordPress sites using Gravity Forms <= 2.7.3
• Any web application integrating the vulnerable Gravity Forms component

Discovery Timeline

• 2023-12-20 - CVE-2023-28782 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-28782

Vulnerability Analysis

This vulnerability stems from insecure deserialization practices within the Gravity Forms WordPress plugin. When user-controlled data is passed to PHP's unserialize() function without proper validation, attackers can inject malicious serialized objects. Upon deserialization, these objects can trigger dangerous "magic methods" (such as __wakeup(), __destruct(), or __toString()) present in the application's codebase or its dependencies, leading to arbitrary code execution.

The unauthenticated nature of this vulnerability significantly increases its risk profile, as no prior authentication is required to exploit it. Attackers with network access to vulnerable WordPress installations can craft malicious payloads that, when processed by the vulnerable deserialization routine, execute attacker-controlled code on the server.

Root Cause

The root cause is the use of PHP's unserialize() function on user-controllable input without adequate sanitization or type checking. Gravity Forms versions through 2.7.3 fail to properly validate serialized data before processing, allowing attackers to inject arbitrary PHP objects. When combined with gadget chains available in WordPress core or common plugins, this can lead to complete system compromise.

Attack Vector

This vulnerability is exploitable over the network without requiring authentication or user interaction. An attacker can send specially crafted HTTP requests containing malicious serialized PHP objects to vulnerable Gravity Forms endpoints. The attack flow typically involves:

1. Identifying a vulnerable Gravity Forms installation (versions through 2.7.3)
2. Crafting a malicious serialized PHP object payload using known gadget chains
3. Sending the payload to a vulnerable endpoint that processes form data
4. The server deserializes the malicious object, triggering code execution

The exploitation relies on the presence of exploitable PHP classes (gadget chains) within the WordPress ecosystem that can be chained together to achieve code execution when their magic methods are invoked during deserialization. Common targets include file operations, database queries, or direct code execution primitives.

Detection Methods for CVE-2023-28782

Indicators of Compromise

• Unusual PHP serialized strings in HTTP request parameters or POST data containing object injection patterns
• Web server logs showing requests with O: prefixed serialized data targeting Gravity Forms endpoints
• Unexpected file modifications or new files in the WordPress installation directory
• Suspicious PHP processes spawned by the web server user

Detection Strategies

• Monitor web application firewall (WAF) logs for serialized PHP object patterns in incoming requests
• Implement input validation rules to detect and block requests containing O: serialization markers
• Deploy endpoint detection to identify unexpected child processes from web server contexts
• Use SentinelOne Singularity to detect post-exploitation behavior such as web shells or lateral movement

Monitoring Recommendations

• Enable detailed logging for Gravity Forms plugin activity and form submissions
• Configure SIEM rules to alert on serialization attack patterns in web traffic
• Monitor for changes to WordPress core files and plugin directories using file integrity monitoring
• Implement real-time alerting for any PHP process execution anomalies on web servers

How to Mitigate CVE-2023-28782

Immediate Actions Required

• Update Gravity Forms to a version higher than 2.7.3 immediately
• Audit WordPress installations for any signs of compromise or unauthorized modifications
• Review web server logs for exploitation attempts targeting Gravity Forms endpoints
• Enable Web Application Firewall (WAF) rules to block PHP object injection attempts

Patch Information

Rocketgenius Inc. has addressed this vulnerability in versions released after 2.7.3. Administrators should update Gravity Forms through the WordPress admin dashboard or by downloading the latest version directly from the Gravity Forms website. After updating, verify the installed version is higher than 2.7.3 by checking the plugin version in WordPress admin under Plugins > Installed Plugins.

For detailed vulnerability information, see the Patchstack Security Advisory.

Workarounds

• If immediate patching is not possible, temporarily disable the Gravity Forms plugin until an update can be applied
• Implement WAF rules to block requests containing serialized PHP object patterns
• Restrict access to form submission endpoints using IP allowlisting where feasible
• Monitor for and block common PHP gadget chain signatures at the network perimeter

# WordPress CLI command to update Gravity Forms
wp plugin update gravityforms

# Verify the installed version
wp plugin list --name=gravityforms --format=table

# Check for recent modifications to plugin files
find /path/to/wordpress/wp-content/plugins/gravityforms -mtime -7 -type f