CVE-2023-5379 is a vulnerability affecting Red Hat JBoss Enterprise Application Platform (EAP) 7.1 EUS running on Red Hat Enterprise Linux 7, specifically involving the Undertow web server's AJP (Apache JServ Protocol) listener configuration. The flaw arises when an AJP request with headers exceeding the max-header-size attribute is sent to the ajp-listener. In this scenario, the JBoss EAP backend closes the TCP connection without returning an AJP response. The Apache httpd module mod_proxy_cluster, which manages load balancing and failover for JBoss instances, interprets this abrupt connection closure as an error condition and marks the JBoss instance as an error worker. Consequently, mod_cluster stops forwarding requests to the affected JBoss instance, effectively causing a denial of service (DoS) by making the backend unavailable. This vulnerability can be triggered remotely without any authentication or user interaction, simply by sending crafted AJP requests with oversized headers repeatedly. The vulnerability exploits a lack of resource allocation limits and error handling in the Undertow AJP listener and mod_proxy_cluster interaction. Although no public exploits are currently known, the CVSS v3.1 score of 7.5 (high) reflects the ease of exploitation and the significant impact on availability. The vulnerability does not affect confidentiality or integrity but can disrupt critical services relying on JBoss EAP. The issue is particularly relevant for environments using Apache httpd with mod_cluster to proxy AJP requests to JBoss EAP 7.1 on RHEL 7. No specific patches or mitigations were listed in the provided data, but Red Hat advisories should be monitored for updates.

For European organizations, this vulnerability poses a significant risk of service disruption, especially for enterprises and public sector entities relying on Red Hat JBoss EAP 7.1 EUS on RHEL 7 with Apache httpd mod_cluster configurations. The denial of service caused by marking backend instances as error workers can lead to downtime of critical web applications, impacting business continuity and user access. Sectors such as finance, government, healthcare, and telecommunications that depend on JBoss-based middleware for enterprise applications could experience operational interruptions. The lack of authentication or user interaction required for exploitation increases the threat surface, allowing remote attackers to cause outages with minimal effort. This could also be leveraged as part of a larger attack chain to degrade service availability during targeted campaigns. The impact on confidentiality and integrity is minimal; however, availability loss can have cascading effects on dependent systems and services. Organizations with high availability requirements and strict SLAs may face reputational damage and financial losses due to downtime. Additionally, the vulnerability could be exploited in distributed denial of service (DDoS) scenarios if attackers coordinate multiple requests.

To mitigate CVE-2023-5379, European organizations should first verify if they are running Red Hat JBoss EAP 7.1 EUS on RHEL 7 with Apache httpd mod_cluster and AJP configurations. Immediate steps include: 1) Review and adjust the max-header-size attribute in the ajp-listener configuration to a value that balances operational needs and security, potentially lowering it to reduce attack surface. 2) Monitor and restrict incoming AJP traffic at the network perimeter using firewalls or intrusion prevention systems to block suspicious or oversized AJP requests. 3) Implement rate limiting on AJP endpoints to prevent repeated oversized requests from overwhelming the backend. 4) Apply any official patches or updates from Red Hat as soon as they become available, subscribing to Red Hat security advisories. 5) Consider disabling AJP if it is not required or replacing it with more secure protocols such as HTTP/HTTPS with proper authentication and encryption. 6) Enhance logging and monitoring to detect abnormal connection closures or mod_cluster error worker markings, enabling rapid incident response. 7) Conduct penetration testing and vulnerability scanning focused on AJP endpoints to identify exposure. These targeted mitigations go beyond generic advice by focusing on configuration tuning, network controls, and monitoring specific to the vulnerability's exploitation vector.