CVE-2023-5379 is a vulnerability identified in the Undertow web server component used by Red Hat JBoss Enterprise Application Platform (EAP) 7.1 EUS running on Red Hat Enterprise Linux 7. The flaw arises when an Apache JServ Protocol (AJP) request exceeds the configured max-header-size attribute in the ajp-listener configuration. Under these conditions, the JBoss EAP instance enters an error state as detected by mod_cluster in the Apache httpd server. Specifically, when the backend JBoss EAP closes the TCP connection without returning an AJP response due to the oversized header, mod_proxy_cluster marks the instance as an error worker and ceases forwarding requests to it. This behavior can be exploited by an unauthenticated attacker who repeatedly sends AJP requests with headers exceeding the max-header-size, causing a denial of service by effectively taking the JBoss EAP instance offline from the load balancer's perspective. The vulnerability has a CVSS 3.1 score of 7.5 (high), reflecting its network attack vector, low complexity, no privileges or user interaction required, and a significant impact on confidentiality due to the potential for service disruption and information exposure through error states. While no public exploits are known, the vulnerability's nature makes it a viable target for denial of service attacks against enterprise applications relying on JBoss EAP 7.1 and mod_cluster setups. The issue highlights the importance of proper resource allocation and request size validation in AJP connectors and load balancing modules.

For European organizations, the primary impact of CVE-2023-5379 is the potential for denial of service against critical enterprise applications hosted on Red Hat JBoss EAP 7.1 on RHEL 7. This can disrupt business operations, degrade service availability, and potentially expose sensitive data through error states or misconfigurations. Industries such as finance, government, telecommunications, and manufacturing that rely on JBoss EAP for middleware services are particularly vulnerable. The disruption caused by mod_cluster marking backend instances as error workers can lead to load balancing failures and service outages, impacting end-users and business continuity. Additionally, the vulnerability could be leveraged as part of a larger attack chain to degrade defenses or distract security teams. Given the widespread use of Red Hat products in Europe and the critical role of JBoss EAP in enterprise Java applications, the threat poses a significant operational risk, especially in countries with large enterprise IT infrastructures and digital services dependent on these platforms.

1. Apply official patches from Red Hat as soon as they become available to address the vulnerability in Undertow and mod_cluster components. 2. Review and tighten the max-header-size configuration in the ajp-listener to reasonable limits that prevent oversized headers without impacting legitimate traffic. 3. Implement monitoring and alerting on mod_cluster error states and backend instance health to detect early signs of exploitation or misconfiguration. 4. Use network-level controls such as firewalls or intrusion prevention systems to detect and block AJP requests with headers exceeding expected sizes. 5. Consider disabling or restricting AJP connectors if not required, or isolate them behind secure network segments to reduce exposure. 6. Conduct regular security assessments and penetration tests focusing on load balancer and backend communication protocols. 7. Educate operations teams about this vulnerability and ensure incident response plans include steps to handle mod_cluster-related DoS scenarios. 8. Evaluate alternative load balancing or proxy solutions if mod_cluster is critical and cannot be adequately secured.