CVE-2024-55636: Drupal Core RCE Vulnerability

CVE-2024-55636 Overview

CVE-2024-55636 is a critical insecure deserialization vulnerability affecting Drupal Core that enables Object Injection attacks. The vulnerability exists because Drupal Core contains a chain of methods (commonly known as a "gadget chain") that can be exploited when an insecure deserialization condition exists on the site. While the gadget chain itself does not present a direct threat, it serves as a vector that attackers can leverage to achieve remote code execution if the application deserializes untrusted data due to another vulnerability in the system.

Critical Impact

This vulnerability enables attackers to potentially achieve remote code execution through object injection when combined with other deserialization flaws, posing a severe risk to Drupal installations with network-accessible attack vectors requiring no authentication.

Affected Products

• Drupal Core versions 8.0.0 through 10.2.10 (fixed in 10.2.11)
• Drupal Core versions 10.3.0 through 10.3.8 (fixed in 10.3.9)
• Drupal Core versions 11.0.0 through 11.0.7 (fixed in 11.0.8)

Discovery Timeline

• 2024-12-10 - CVE-2024-55636 published to NVD
• 2025-06-02 - Last updated in NVD database

Technical Details for CVE-2024-55636

Vulnerability Analysis

This vulnerability falls under CWE-502 (Deserialization of Untrusted Data) and CWE-915 (Improperly Controlled Modification of Dynamically-Determined Object Attributes). The core issue stems from the presence of exploitable gadget chains within Drupal Core that can be weaponized when untrusted data is deserialized.

In PHP applications like Drupal, object injection vulnerabilities occur when user-controllable data is passed to the unserialize() function. When malicious serialized objects are deserialized, they can trigger special "magic methods" such as __wakeup(), __destruct(), or __toString(). Attackers craft serialized payloads that chain together multiple class methods (gadget chains) to achieve arbitrary code execution.

The network-accessible nature of this vulnerability, combined with the lack of required privileges or user interaction, makes it particularly dangerous for internet-facing Drupal installations. An attacker exploiting this vulnerability in combination with another deserialization flaw could gain complete control over the affected system.

Root Cause

The root cause is the presence of exploitable gadget chains within Drupal Core's codebase. These gadget chains consist of sequences of class methods that, when triggered during deserialization, can be manipulated to perform unintended actions. While Drupal Core should not directly deserialize untrusted user input, the existence of these gadget chains creates a risk when combined with other vulnerabilities that may introduce unsafe deserialization points—such as contributed modules, custom code, or additional security flaws.

Attack Vector

The attack vector is network-based, requiring no privileges or user interaction. An attacker would need to identify or introduce a deserialization entry point on the target Drupal site. Once such an entry point exists, the attacker can craft a malicious serialized PHP object that leverages Drupal Core's internal gadget chain. When the payload is deserialized, the gadget chain executes, potentially allowing:

• Arbitrary PHP code execution on the server
• File system manipulation (read, write, delete files)
• Database access and data exfiltration
• Lateral movement within the network
• Complete server compromise

The attack typically involves crafting a serialized payload containing malicious objects that exploit the __destruct() or __wakeup() magic methods to trigger the gadget chain. For detailed technical information, refer to the Drupal Security Advisory SA-CORE-2024-006.

Detection Methods for CVE-2024-55636

Indicators of Compromise

• Unexpected serialized PHP data in HTTP request parameters, cookies, or POST bodies
• Unusual patterns in web server logs containing base64-encoded or serialized object data
• Unexplained file modifications in Drupal installation directories
• Creation of new PHP files or web shells in accessible directories
• Anomalous outbound network connections from the web server

Detection Strategies

• Monitor web application firewall (WAF) logs for serialized PHP object patterns in requests
• Implement signature-based detection for common PHP deserialization attack payloads
• Audit Drupal Core and contributed module versions against known vulnerable versions
• Review server access logs for suspicious requests targeting endpoints that may handle serialized data

Monitoring Recommendations

• Enable detailed PHP error logging to capture deserialization-related errors
• Configure intrusion detection systems to alert on PHP object injection patterns
• Implement file integrity monitoring on critical Drupal directories
• Monitor for unexpected process spawning from the web server process

How to Mitigate CVE-2024-55636

Immediate Actions Required

• Upgrade Drupal Core to version 10.2.11, 10.3.9, or 11.0.8 immediately
• Audit all contributed modules and custom code for potential deserialization entry points
• Review and restrict network access to the Drupal administrative interface
• Implement web application firewall rules to block serialized object payloads

Patch Information

Drupal has released security patches addressing this vulnerability. Administrators should upgrade to the following fixed versions:

• Drupal 10.2.x: Upgrade to 10.2.11 or later
• Drupal 10.3.x: Upgrade to 10.3.9 or later
• Drupal 11.0.x: Upgrade to 11.0.8 or later

For complete patch details and upgrade instructions, see the Drupal Security Advisory SA-CORE-2024-006.

Workarounds

• If immediate patching is not possible, implement strict input validation on all entry points
• Configure PHP's unserialize_allowed_classes option to restrict deserialization to known safe classes
• Deploy a web application firewall with rules specifically designed to detect PHP serialization attacks
• Conduct a thorough security audit of contributed modules that may handle user-supplied data

# Drupal upgrade commands using Composer
composer update drupal/core "drupal/core-*" --with-all-dependencies
drush updatedb
drush cache:rebuild