CVE-2024-5971 is a vulnerability discovered in the Undertow web server framework, which is widely used in Java applications for handling HTTP requests and responses. The issue arises specifically when Undertow is deployed on Java 17 environments utilizing TLS 1.3. During chunked transfer encoding responses, Undertow fails to send the terminating chunk sequence (0\r\n) after flushing the response body. Although the response headers and body are transmitted, the client continues to wait for the termination signal, causing the connection to hang. This behavior leads to uncontrolled recursion in resource consumption on the server side, as connections remain open and resources are not released properly. The vulnerability does not compromise confidentiality or integrity but severely impacts availability by enabling denial of service attacks. The CVSS v3.1 base score is 7.5 (high), reflecting network attack vector, low attack complexity, no privileges required, no user interaction, and an impact limited to availability. No public exploits have been reported yet, but the flaw is critical for environments using Undertow versions up to 2.3.0.Alpha1 on Java 17 with TLS 1.3. The root cause is a protocol handling bug in chunked transfer encoding implementation under these specific conditions.

The primary impact of CVE-2024-5971 is denial of service due to resource exhaustion on servers running vulnerable Undertow versions with Java 17 TLS 1.3. Attackers can exploit this remotely without authentication or user interaction by sending specially crafted HTTP requests that trigger the chunked response hang. This can lead to server unavailability, degraded performance, and potential downtime for web applications relying on Undertow. Organizations with critical services exposed to the internet using this stack may face operational disruptions and reputational damage. Since the vulnerability affects availability only, data confidentiality and integrity remain intact. However, prolonged denial of service can indirectly affect business continuity and customer trust. The lack of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits following public disclosure.

To mitigate CVE-2024-5971, organizations should first upgrade Undertow to a patched version beyond 2.3.0.Alpha1 once available from official maintainers. Until patches are released, consider the following specific actions: 1) Disable or avoid using TLS 1.3 on Java 17 environments running Undertow if feasible, reverting to TLS 1.2 to prevent triggering the bug. 2) Implement rate limiting and connection timeouts on HTTP endpoints to reduce the impact of hanging connections. 3) Monitor server resource usage and connection states to detect abnormal accumulation of hanging chunked responses. 4) Use web application firewalls (WAFs) or reverse proxies to filter or block suspicious chunked transfer requests. 5) Review and update Java runtime environments and Undertow configurations to ensure compatibility and stability. 6) Conduct thorough testing in staging environments before deploying changes to production. These targeted mitigations go beyond generic advice by focusing on the specific conditions that trigger the vulnerability.