CVE-2024-35176 is a denial of service (DoS) vulnerability classified under CWE-400 (Uncontrolled Resource Consumption) and CWE-770 (Allocation of Resources Without Limits or Throttling) affecting the Ruby REXML gem versions prior to 3.2.7. REXML is a pure Ruby XML toolkit widely used for XML parsing. The vulnerability occurs when REXML parses XML documents containing attribute values with a large number of '<' characters. This malformed input causes excessive resource consumption, such as CPU and memory, leading to application slowdown or crash, effectively resulting in a denial of service. The vulnerability can be triggered remotely without requiring authentication or user interaction, making it exploitable in network-facing applications that parse untrusted XML inputs. The root cause is insufficient input validation and lack of resource usage limits during XML parsing. The issue was addressed in REXML version 3.2.7 by implementing proper input handling and resource consumption controls. No public exploits have been reported yet, but the vulnerability's nature makes it a credible threat to availability in affected environments. Organizations using REXML in Ruby applications that handle untrusted XML should prioritize upgrading to version 3.2.7 or later. As a temporary mitigation, avoiding parsing untrusted XML inputs can reduce exposure.

For European organizations, this vulnerability primarily threatens the availability of services relying on Ruby applications that use the REXML gem for XML parsing. Denial of service attacks exploiting this vulnerability could disrupt business-critical applications, especially those processing XML data from external or untrusted sources, such as web services, APIs, or integration platforms. This could lead to downtime, degraded performance, and potential loss of customer trust. Sectors such as finance, healthcare, government, and telecommunications, which often handle XML-based data exchanges, may face operational interruptions. Additionally, organizations with automated workflows or DevOps pipelines using Ruby scripts for XML processing might experience cascading failures. While confidentiality and integrity are not directly impacted, the availability disruption could have significant operational and reputational consequences. The medium CVSS score (5.3) reflects moderate severity, but the ease of exploitation without authentication increases the risk profile. Proactive mitigation is essential to prevent service outages and maintain compliance with European cybersecurity regulations.

1. Upgrade all Ruby environments using the REXML gem to version 3.2.7 or later immediately to apply the official patch. 2. Audit all applications and services that parse XML data to identify usage of vulnerable REXML versions. 3. Implement input validation and sanitization to reject XML inputs containing suspiciously large numbers of '<' characters or other malformed constructs before parsing. 4. Where possible, avoid parsing XML from untrusted or unauthenticated sources. 5. Introduce resource limits and timeouts on XML parsing operations to prevent excessive CPU or memory consumption. 6. Monitor application logs and resource usage metrics for signs of abnormal spikes during XML processing. 7. Employ Web Application Firewalls (WAFs) or XML gateways that can detect and block malicious XML payloads targeting this vulnerability. 8. Educate development teams about secure XML parsing practices and the risks of uncontrolled resource consumption. 9. Establish incident response plans to quickly address denial of service events related to XML parsing. 10. Regularly review and update dependencies to incorporate security patches promptly.