CVE-2023-26326: BuddyForms WordPress Plugin RCE Vulnerability

CVE-2023-26326 Overview

The BuddyForms WordPress plugin, in versions prior to 2.7.8, contains an unauthenticated insecure deserialization vulnerability. An unauthenticated attacker can exploit this issue by leveraging a PHAR wrapper to call files that will deserialize data and execute arbitrary PHP Objects. When combined with a suitable POP (Property-Oriented Programming) chain, this vulnerability enables a variety of malicious actions including remote code execution.

Critical Impact

Unauthenticated attackers can achieve remote code execution on WordPress sites running vulnerable versions of the BuddyForms plugin by exploiting insecure deserialization with PHAR wrapper techniques.

Affected Products

• ThemeKraft BuddyForms versions prior to 2.7.8
• WordPress installations with vulnerable BuddyForms plugin installed and active

Discovery Timeline

• 2023-02-23 - CVE-2023-26326 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-26326

Vulnerability Analysis

This vulnerability is classified as CWE-502 (Deserialization of Untrusted Data). The BuddyForms plugin fails to properly validate and sanitize user-controlled input before passing it to PHP's deserialization functions. The vulnerability is particularly severe because it requires no authentication, allowing any remote attacker to exploit it.

The attack leverages PHP's PHAR (PHP Archive) deserialization mechanism. When a PHAR file is accessed via a stream wrapper (e.g., phar://), PHP automatically deserializes the metadata stored within the archive. If an attacker can control the path used in a file operation and a PHAR file with malicious serialized objects exists on the system, they can trigger arbitrary object instantiation.

Root Cause

The root cause lies in the plugin's improper handling of user-supplied input in file operations. The plugin does not adequately validate or sanitize paths before using them in operations that support stream wrappers. This allows attackers to inject PHAR wrapper references that trigger PHP's automatic deserialization of PHAR metadata, leading to object injection.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Uploading or positioning a malicious PHAR file containing a crafted serialized payload on the target system
2. Triggering a file operation in the BuddyForms plugin using the phar:// wrapper pointing to the malicious file
3. PHP automatically deserializes the PHAR metadata, instantiating the attacker-controlled objects
4. If a suitable POP chain exists in the application or its dependencies, the attacker achieves arbitrary code execution

The exploitation requires a POP chain to be present in the WordPress installation or its plugins/themes. Common WordPress plugins often provide gadget chains that can be leveraged for this purpose.

For detailed technical analysis, see the Tenable Security Research Advisory.

Detection Methods for CVE-2023-26326

Indicators of Compromise

• Suspicious web requests containing phar:// wrapper references in request parameters
• Unusual file access patterns targeting PHAR archive files
• Unexpected PHP object instantiation in WordPress error logs
• Web server logs showing requests with serialized PHP data or PHAR wrapper paths

Detection Strategies

• Monitor web application logs for requests containing phar:// or other PHP stream wrapper references
• Implement Web Application Firewall (WAF) rules to detect and block PHAR deserialization attempts
• Audit installed WordPress plugins for versions of BuddyForms prior to 2.7.8
• Deploy file integrity monitoring on WordPress installations to detect unauthorized PHAR files

Monitoring Recommendations

• Enable verbose logging for WordPress and the web server to capture detailed request information
• Configure security monitoring tools to alert on PHP deserialization-related error messages
• Implement network-level monitoring for unusual file upload patterns that could indicate PHAR staging
• Regularly scan plugin directories for unexpected or suspicious file types

How to Mitigate CVE-2023-26326

Immediate Actions Required

• Update BuddyForms plugin immediately to version 2.7.8 or later
• If immediate patching is not possible, temporarily deactivate the BuddyForms plugin until it can be updated
• Review server logs for evidence of exploitation attempts
• Conduct a security audit of the WordPress installation to identify any signs of compromise

Patch Information

ThemeKraft has addressed this vulnerability in BuddyForms version 2.7.8. Users should update to this version or later through the WordPress plugin repository. The update can be applied via the WordPress admin dashboard under Plugins > Installed Plugins, or by using WP-CLI.

For more information, refer to the Tenable Security Research Advisory.

Workarounds

• Implement WAF rules to block requests containing phar:// and other potentially dangerous PHP stream wrappers
• Restrict file upload capabilities and validate file types at the server level
• Use PHP configuration to disable the PHAR stream wrapper if not required: stream_wrapper_unregister('phar');
• Apply principle of least privilege to WordPress file permissions to limit potential PHAR file staging locations

# Configuration example - Disable PHAR stream wrapper in PHP
# Add to wp-config.php or custom PHP initialization file
# This prevents PHAR deserialization attacks site-wide

# Option 1: Add to wp-config.php (before "That's all, stop editing!")
# stream_wrapper_unregister('phar');

# Option 2: Check current plugin version via WP-CLI
wp plugin list --name=buddyforms --fields=name,version,update_version

# Option 3: Update BuddyForms via WP-CLI
wp plugin update buddyforms