CVE-2024-41123 is a denial-of-service (DoS) vulnerability classified under CWE-400 (Uncontrolled Resource Consumption) affecting the REXML gem, an XML parsing toolkit for Ruby. Versions prior to 3.3.3 are vulnerable due to inefficient handling of XML inputs containing numerous specific characters such as whitespace, ">]", and "]>" sequences. When parsing such crafted XML documents, the REXML parser consumes excessive CPU and memory resources, potentially exhausting system resources and causing application or service unavailability. The vulnerability does not impact confidentiality or integrity but affects availability by enabling attackers to degrade or disrupt services. Exploitation requires no privileges or user interaction and can be triggered remotely by submitting malicious XML payloads to applications that parse XML using the vulnerable REXML versions. The issue was addressed in REXML version 3.3.3 with patches that optimize parsing logic to prevent resource exhaustion. No known exploits are currently reported in the wild, but the medium CVSS score of 5.3 reflects the moderate impact and ease of exploitation. Organizations using Ruby applications that rely on REXML for XML processing should assess their dependency versions and apply updates promptly to mitigate this risk.

For European organizations, this vulnerability poses a risk primarily to availability of services that utilize Ruby applications with vulnerable REXML versions. Industries such as finance, healthcare, government, and telecommunications that process XML data in backend systems or APIs may experience service disruptions or outages if targeted. Denial-of-service attacks exploiting this vulnerability could lead to operational downtime, impacting business continuity and potentially causing financial losses or regulatory compliance issues. Since no authentication or user interaction is required, attackers can remotely trigger the DoS condition, increasing the threat surface. The impact is more pronounced for organizations with high XML processing workloads or exposed XML interfaces. While no data breach or integrity compromise is involved, the availability impact can degrade user trust and service reliability. Given the widespread use of Ruby in web applications and automation tools, the vulnerability could affect a broad range of sectors across Europe.

European organizations should take the following specific mitigation steps: 1) Identify all Ruby environments and applications using the REXML gem and determine the version in use. 2) Upgrade REXML to version 3.3.3 or later, which contains patches addressing the resource consumption issue. 3) If immediate upgrade is not feasible, implement input validation and filtering to detect and block XML payloads containing suspicious patterns such as excessive whitespace or problematic character sequences (">]", "]>"). 4) Employ rate limiting and anomaly detection on XML processing endpoints to mitigate potential abuse. 5) Monitor application logs and resource usage metrics for unusual spikes during XML parsing operations. 6) Consider deploying Web Application Firewalls (WAFs) with custom rules to detect and block malicious XML payloads targeting this vulnerability. 7) Incorporate this vulnerability into vulnerability management and patching cycles to ensure timely updates. 8) Educate developers and DevOps teams about secure XML parsing practices and the importance of using updated libraries.