CVE-2020-28032: WordPress Deserialization Vulnerability

CVE-2020-28032 Overview

CVE-2020-28032 is a critical insecure deserialization vulnerability affecting WordPress versions prior to 5.5.2. The flaw exists in the wp-includes/Requests/Utility/FilteredIterator.php file, where deserialization requests are improperly handled. This vulnerability allows remote attackers to potentially achieve arbitrary code execution by exploiting the unsafe deserialization of user-controlled data.

Critical Impact

Remote attackers can exploit this deserialization flaw without authentication, potentially leading to complete system compromise including unauthorized access, data manipulation, and server takeover.

Affected Products

• WordPress versions prior to 5.5.2
• Fedora Linux 31, 32, and 33
• Debian Linux 9.0 and 10.0

Discovery Timeline

• 2020-10-29 - WordPress releases security patch in version 5.5.2
• 2020-11-02 - CVE-2020-28032 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-28032

Vulnerability Analysis

This vulnerability is classified as CWE-502 (Deserialization of Untrusted Data). The FilteredIterator.php component within the WordPress Requests library fails to properly validate and sanitize data before deserialization operations. PHP object injection vulnerabilities of this nature can be particularly dangerous because they allow attackers to inject arbitrary objects into the application's runtime environment.

When exploited, this vulnerability can lead to remote code execution if suitable "gadget chains" exist within the WordPress codebase or installed plugins. The attack can be conducted remotely over the network without requiring any prior authentication or user interaction, making it highly exploitable in real-world scenarios.

Root Cause

The root cause of CVE-2020-28032 lies in the improper handling of deserialization requests within the FilteredIterator class. The component fails to implement adequate validation of serialized data before processing, allowing malicious payloads to be deserialized and executed. This is a common security anti-pattern in PHP applications where unserialize() is called on data that can be influenced by external input.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can craft malicious serialized PHP objects and submit them to the vulnerable WordPress installation. When the FilteredIterator class processes these requests, the malicious objects are deserialized, potentially triggering dangerous magic methods like __destruct() or __wakeup() that can lead to code execution.

The vulnerability manifests in the FilteredIterator.php file within the WordPress Requests library component. When this class deserializes attacker-controlled input, it fails to validate the integrity and safety of the serialized data. Exploitation typically involves crafting a serialized PHP object that, when deserialized, triggers a chain of method calls (gadget chain) that ultimately leads to arbitrary code execution. For detailed technical analysis of the fix, refer to the GitHub WordPress Commit.

Detection Methods for CVE-2020-28032

Indicators of Compromise

• Unusual serialized PHP object payloads in HTTP request parameters, POST data, or cookies containing unexpected class names
• Web server logs showing requests with encoded serialized data targeting WordPress endpoints
• Unexpected PHP processes spawning or network connections originating from the web server
• Modified files in WordPress core directories, particularly within wp-includes/

Detection Strategies

• Monitor web application firewall (WAF) logs for patterns indicative of PHP object injection attempts
• Implement intrusion detection rules to identify serialized PHP objects in inbound HTTP traffic
• Review WordPress error logs for deserialization-related exceptions or warnings
• Deploy file integrity monitoring on WordPress core files to detect unauthorized modifications

Monitoring Recommendations

• Enable comprehensive logging for all HTTP requests to WordPress installations
• Configure SIEM alerts for suspicious patterns in web traffic targeting PHP applications
• Implement real-time monitoring for process creation and network connections from web server contexts
• Regularly audit WordPress version and ensure patch compliance across all installations

How to Mitigate CVE-2020-28032

Immediate Actions Required

• Upgrade WordPress immediately to version 5.5.2 or later to address this vulnerability
• Review web server access logs for signs of exploitation attempts
• Implement WAF rules to block serialized PHP object patterns in incoming requests
• Audit installed plugins and themes for additional deserialization vulnerabilities

Patch Information

WordPress addressed this vulnerability in version 5.5.2, released in October 2020. The security fix modifies how the FilteredIterator class handles deserialization requests to prevent malicious object injection. Organizations should apply this update immediately as the vulnerability is remotely exploitable without authentication.

For detailed patch information, see the WordPress 5.5.2 Security Release announcement and the GitHub WordPress Commit.

Distribution-specific patches are available via Debian Security Advisory DSA-4784 and Fedora package announcements.

Workarounds

• Deploy a web application firewall with rules to block PHP serialized object patterns in HTTP requests
• Restrict network access to WordPress admin interfaces and sensitive endpoints
• Implement PHP runtime protections such as disable_functions to limit dangerous function calls
• Consider using a security plugin that provides virtual patching capabilities until the update can be applied

# Verify WordPress version and update
wp core version
wp core update

# Check for file integrity issues
wp core verify-checksums

# Review access logs for exploitation attempts
grep -E "(serialize|unserialize|FilteredIterator)" /var/log/apache2/access.log