CVE-2024-5971 is a vulnerability discovered in the Undertow web server framework, specifically affecting its handling of HTTP chunked transfer encoding responses when running on Java 17 with TLSv1.3 enabled. Normally, chunked transfer encoding requires the server to send a terminating chunk of "0\r\n" to signal the end of the response body. Due to this flaw, Undertow sends the response headers and body but fails to send the terminating chunk, causing the client to wait indefinitely for the completion signal. This hanging state leads to uncontrolled resource consumption on the server side, as connections remain open and resources tied up, effectively enabling a denial of service (DoS) attack. The vulnerability is remotely exploitable without any authentication or user interaction, increasing its risk profile. It affects Undertow versions from 0 up to 2.3.0.Alpha1. The CVSS v3.1 base score is 7.5, reflecting high severity due to the impact on availability and ease of exploitation over the network. No known exploits have been reported in the wild yet, but the vulnerability poses a significant risk to services relying on Undertow in Java 17 TLSv1.3 environments. The issue is particularly relevant for applications that handle high volumes of HTTP requests and rely on chunked transfer encoding for streaming or large responses. The root cause lies in the improper handling of the chunked response termination sequence, which is a protocol-level defect. Until a patch is released, affected users must consider mitigation strategies to prevent resource exhaustion and service disruption.

For European organizations, this vulnerability presents a serious risk to the availability of web services and applications using Undertow on Java 17 with TLSv1.3. The uncontrolled resource consumption can lead to denial of service conditions, potentially disrupting critical business operations, customer-facing portals, and internal services. Industries such as finance, healthcare, government, and telecommunications, which often deploy Java-based middleware and web servers, could experience outages or degraded performance. The lack of required authentication or user interaction for exploitation means attackers can remotely trigger the DoS condition, increasing the attack surface. Additionally, the vulnerability could be leveraged as part of a larger attack chain to distract or disable defenses. Given the widespread use of Java and Undertow in enterprise environments across Europe, the impact could be significant, especially for organizations with high traffic volumes or those that rely on TLSv1.3 for secure communications. The absence of known exploits in the wild provides a window for proactive mitigation, but the potential for rapid exploitation remains.

1. Monitor Undertow project communications and promptly apply official patches or updates once released that address CVE-2024-5971. 2. If immediate patching is not possible, consider disabling TLSv1.3 temporarily or reverting to an earlier Java version where the issue does not manifest, understanding the trade-offs in security and compatibility. 3. Implement rate limiting and connection timeouts at the web server or network edge to limit the impact of hanging connections and resource exhaustion. 4. Use web application firewalls (WAFs) or intrusion prevention systems (IPS) to detect and block abnormal request patterns that could trigger the vulnerability. 5. Conduct thorough testing of Undertow-based applications in staging environments with Java 17 TLSv1.3 to identify if they are affected and to validate mitigation strategies. 6. Review and optimize server resource allocation and monitoring to quickly detect unusual resource consumption indicative of exploitation attempts. 7. Educate development and operations teams about the vulnerability to ensure rapid response and awareness. 8. Consider architectural changes to reduce reliance on chunked transfer encoding where feasible or implement alternative response handling mechanisms.