CVE-2024-39908: Ruby-lang Rexml DoS Vulnerability

CVE-2024-39908 Overview

CVE-2024-39908 is a Denial of Service (DoS) vulnerability affecting REXML, an XML toolkit for Ruby. The REXML gem before version 3.3.1 contains DoS vulnerabilities when parsing XML documents that contain many specific characters such as <, 0, and %>. Applications that parse untrusted XML input using vulnerable versions of REXML may be susceptible to resource exhaustion attacks.

Critical Impact

Applications processing untrusted XML data with vulnerable REXML versions can be targeted for denial of service attacks, potentially causing service disruption and resource exhaustion.

Affected Products

• ruby-lang rexml (versions before 3.3.1)
• netapp bootstrap_os
• netapp hci_compute_node

Discovery Timeline

• 2024-07-16 - CVE-2024-39908 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2024-39908

Vulnerability Analysis

This vulnerability is classified as CWE-400 (Uncontrolled Resource Consumption). The REXML parser experiences significant performance degradation when processing XML documents containing specific character sequences. When maliciously crafted XML input with repeated patterns of characters like <, 0, and %> is submitted to an application using a vulnerable REXML version, the parser consumes excessive computational resources attempting to process the input.

The vulnerability is exploitable over the network and requires user interaction (such as uploading or submitting an XML file). While the impact is limited to availability (denial of service) without affecting confidentiality or integrity, it can disrupt services that rely on XML parsing functionality.

Root Cause

The root cause lies in inefficient handling of specific character sequences within the REXML parsing logic. When the parser encounters XML documents containing many instances of characters like <, 0, and %>, the parsing algorithm exhibits poor performance characteristics, leading to resource exhaustion. This is a classic algorithmic complexity vulnerability where certain inputs trigger worst-case processing behavior.

Attack Vector

The attack vector is network-based, requiring an attacker to submit crafted XML content to a vulnerable application. The attack scenario involves:

1. Identifying an application endpoint that accepts XML input and uses REXML for parsing
2. Crafting an XML document containing repeated sequences of the problematic characters (<, 0, %>)
3. Submitting the malicious XML to the target application
4. The REXML parser consumes excessive CPU/memory resources attempting to process the input
5. Service degradation or complete denial of service occurs

The vulnerability requires no authentication but does require user interaction to trigger the XML parsing functionality.

Detection Methods for CVE-2024-39908

Indicators of Compromise

• Unusually high CPU utilization on servers processing XML input
• Memory exhaustion alerts from application monitoring systems
• Increased response times or timeouts on XML processing endpoints
• Application logs showing XML parsing operations taking abnormally long
• Repeated submissions of large or unusual XML documents to parsing endpoints

Detection Strategies

• Monitor application resource consumption during XML parsing operations for anomalies
• Implement logging to track XML document sizes and parsing durations
• Set up alerts for CPU or memory spikes correlated with XML processing activities
• Audit Ruby gem dependencies to identify vulnerable REXML versions (before 3.3.1)
• Use software composition analysis (SCA) tools to detect vulnerable REXML installations

Monitoring Recommendations

• Configure application performance monitoring to track XML parsing latency
• Set resource consumption thresholds and alerts on services handling XML input
• Enable detailed logging for XML processing endpoints to identify suspicious patterns
• Monitor for repeated failed or timeout XML parsing operations

How to Mitigate CVE-2024-39908

Immediate Actions Required

• Upgrade REXML gem to version 3.3.2 or later which includes patches for this vulnerability
• Audit all Ruby applications to identify those using vulnerable REXML versions
• Implement input validation to limit XML document size before parsing
• Consider implementing request rate limiting on endpoints that process XML input
• Temporarily disable XML processing endpoints if immediate patching is not possible

Patch Information

The REXML gem version 3.3.2 or later includes patches that fix these DoS vulnerabilities. Users should upgrade to the latest available version to receive the security fixes. For detailed patch information, refer to the GitHub Security Advisory and the official Ruby-lang security announcement. Additional vendor-specific guidance is available from the NetApp Security Advisory and the Debian LTS Announcement.

Workarounds

• Avoid parsing untrusted XML strings with vulnerable REXML versions
• Implement XML document size limits at the application or web server level
• Use alternative XML parsing libraries if REXML upgrade is not immediately possible
• Deploy a web application firewall (WAF) to filter potentially malicious XML payloads

# Upgrade REXML gem to patched version
gem update rexml

# Or specify minimum version in Gemfile
# gem 'rexml', '>= 3.3.2'
bundle update rexml