CVE-2025-11230 identifies a vulnerability in HAProxy Community Edition related to inefficient algorithmic complexity within the mjson JSON parsing library. Specifically, the vulnerability arises because the JSON parser does not efficiently handle certain crafted JSON inputs, leading to excessive computational resource consumption. This inefficiency can be exploited remotely by attackers who send specially crafted JSON requests to HAProxy instances, causing the service to consume excessive CPU or memory resources, ultimately resulting in a denial of service (DoS) condition. The vulnerability affects multiple versions of HAProxy Community Edition, from 2.4.0 through 3.2.0, indicating a broad impact across recent releases. The CVSS 3.1 base score of 7.5 reflects a high severity rating, with the vector indicating network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), no impact on confidentiality or integrity (C:N/I:N), but high impact on availability (A:H). No patches were listed at the time of publication, and no known exploits have been observed in the wild, but the vulnerability's characteristics suggest it could be weaponized for DoS attacks against HAProxy deployments. HAProxy is widely used as a high-performance TCP/HTTP load balancer and proxy, often deployed in front of web applications and APIs, making this vulnerability particularly relevant for internet-facing infrastructure.

For European organizations, the primary impact of CVE-2025-11230 is the potential for denial of service attacks that can disrupt critical web services and applications relying on HAProxy for load balancing and proxy functions. This can lead to service outages, degraded user experience, and potential financial losses, especially for sectors such as finance, e-commerce, telecommunications, and public services that depend on high availability. The vulnerability does not compromise confidentiality or integrity directly but threatens availability, which can indirectly affect business continuity and trust. Organizations with large-scale or high-traffic HAProxy deployments are at greater risk, as attackers can exploit the inefficient JSON parsing to exhaust server resources rapidly. Additionally, the lack of required authentication and user interaction lowers the barrier for attackers, increasing the likelihood of exploitation attempts. The absence of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, especially as public knowledge of the vulnerability grows.

To mitigate CVE-2025-11230, European organizations should prioritize the following actions: 1) Monitor HAProxy vendor communications closely and apply official patches or updates as soon as they become available to address the inefficient algorithmic complexity in mjson. 2) Implement network-level rate limiting and filtering to restrict the volume and frequency of JSON requests reaching HAProxy instances, reducing the risk of resource exhaustion. 3) Deploy Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) with rules designed to detect and block anomalous or malformed JSON payloads that could trigger the vulnerability. 4) Conduct regular performance and resource usage monitoring on HAProxy servers to detect unusual spikes indicative of exploitation attempts. 5) Where feasible, isolate HAProxy instances behind additional proxy layers or use containerization to limit the impact of potential DoS attacks. 6) Review and harden JSON input validation in upstream applications to reduce reliance on HAProxy for filtering malformed requests. 7) Educate security and operations teams about the vulnerability and signs of exploitation to enable rapid response. These measures go beyond generic advice by focusing on proactive detection, containment, and layered defense tailored to the nature of this algorithmic complexity vulnerability.