CVE-2024-42516 is an HTTP response splitting vulnerability rooted in improper input validation (CWE-20) within the Apache HTTP Server core, specifically affecting the handling of Content-Type response headers. This flaw allows an attacker who can manipulate these headers to inject malicious payloads that split the HTTP response, potentially enabling various attacks such as HTTP header injection, cache poisoning, cross-site scripting (XSS), and web cache deception. The vulnerability affects all Apache HTTP Server versions starting from 2.4.0 up to 2.4.63. Notably, a prior attempt to fix a similar issue (CVE-2023-38709) in version 2.4.59 was incomplete, leaving the vulnerability exploitable until the release of version 2.4.64, which contains the definitive patch. The CVSS v3.1 score of 7.5 reflects a high severity due to the vulnerability’s network attack vector, low attack complexity, no required privileges or user interaction, and a significant impact on data integrity. Although no public exploits have been reported, the vulnerability’s characteristics make it a viable target for attackers aiming to manipulate web server responses to compromise client security or disrupt web services. The flaw’s exploitation could undermine trust in web communications, enabling attackers to inject malicious content or manipulate cached responses, thereby affecting the confidentiality and integrity of data exchanged via the server.

For European organizations, the impact of CVE-2024-42516 can be substantial, especially for those operating critical web infrastructure or providing web services to customers. Exploitation could lead to HTTP response splitting attacks that enable injection of malicious headers or content, potentially facilitating cross-site scripting, session hijacking, or cache poisoning. This undermines the integrity of web communications and can lead to data manipulation or exposure of sensitive information. Organizations in sectors such as finance, government, healthcare, and e-commerce are particularly vulnerable due to the sensitive nature of their data and the reliance on Apache HTTP Server for web hosting or proxying. Additionally, compromised web responses can damage organizational reputation and erode user trust. Given the widespread deployment of Apache HTTP Server across Europe, failure to patch this vulnerability could result in large-scale exploitation attempts targeting European digital infrastructure, disrupting services and exposing users to further downstream attacks.

European organizations should immediately upgrade all affected Apache HTTP Server instances to version 2.4.64 or later, which contains the definitive fix for this vulnerability. Beyond upgrading, organizations should implement strict input validation and sanitization on all user-controllable headers, especially Content-Type headers, to prevent injection of malicious payloads. Employing web application firewalls (WAFs) with rules designed to detect and block HTTP response splitting attempts can provide an additional layer of defense. Regularly auditing and monitoring HTTP response headers for anomalies can help detect exploitation attempts early. Organizations should also review proxy and reverse proxy configurations to ensure they do not inadvertently forward manipulated headers. Finally, integrating vulnerability scanning and patch management processes that prioritize critical web infrastructure will reduce the window of exposure to similar vulnerabilities in the future.