CVE-2024-1300 is a vulnerability identified in Eclipse Vert.x version 4.3.4, a popular toolkit for building reactive applications on the JVM. The flaw arises in the handling of TLS connections with Server Name Indication (SNI) support enabled on TCP servers. When the server receives a TLS client hello message containing an unknown or unmapped SNI server name, instead of rejecting or properly handling this input, the server assigns the default certificate but erroneously caches the SSL context associated with this default certificate in the server name map. This caching behavior leads to a memory leak because each unique unknown SNI name causes a new SSL context to be stored without ever being released, eventually exhausting the Java Virtual Machine (JVM) heap memory. An attacker can exploit this by sending multiple TLS client hello messages with fake or random server names, causing the server to consume increasing amounts of memory until it triggers an out-of-memory error, resulting in denial of service (DoS). The vulnerability requires network access (AV:N) and low privileges (PR:L) but no user interaction (UI:N). The impact is limited to availability (A:L) with no direct confidentiality or integrity compromise. No public exploits have been reported yet, and no official patches were linked at the time of publication. This flaw is particularly relevant for organizations deploying Vert.x-based TCP servers with TLS and SNI enabled, especially in microservices or reactive system architectures.

For European organizations, the primary impact of CVE-2024-1300 is the risk of denial-of-service conditions on critical TCP services that use Eclipse Vert.x 4.3.4 with TLS and SNI support. This can lead to service outages, degraded performance, and potential disruption of business operations relying on reactive Java applications. While the vulnerability does not directly expose sensitive data or allow unauthorized data modification, the availability impact can affect customer-facing services, internal APIs, and inter-service communications. Organizations in sectors such as finance, telecommunications, and government, which often rely on Java-based middleware and microservices, may experience operational risks. Additionally, the JVM out-of-memory errors could trigger cascading failures in containerized or cloud environments, complicating incident response. The absence of known exploits reduces immediate risk, but the ease of triggering the memory leak via crafted TLS handshakes means attackers could weaponize this flaw for targeted DoS attacks. European entities must consider this vulnerability in their risk assessments, especially those with Vert.x deployments exposed to untrusted networks.

To mitigate CVE-2024-1300, organizations should first verify if they are running Eclipse Vert.x version 4.3.4 with TLS and SNI enabled on TCP servers. Immediate mitigation includes restricting network access to these services by implementing firewall rules or network segmentation to limit exposure to untrusted clients. Deploying TLS termination proxies or load balancers that validate SNI values and reject unknown or suspicious server names can prevent malformed TLS handshakes from reaching vulnerable servers. Monitoring JVM memory usage and setting alert thresholds can help detect early signs of exploitation attempts. Administrators should track Eclipse Vert.x updates and apply patches as soon as they become available. In the interim, consider disabling SNI support if feasible or configuring the server to handle unknown SNI names more gracefully, if such configuration options exist. Additionally, employing runtime application self-protection (RASP) or Web Application Firewalls (WAFs) with TLS inspection capabilities may provide further defense. Finally, conducting penetration testing and red team exercises simulating this attack vector can improve detection and response readiness.