CVE-2025-49630 is a high-severity vulnerability affecting Apache HTTP Server versions 2.4.26 through 2.4.63. The issue arises specifically in configurations where Apache is used as a reverse proxy to an HTTP/2 backend, with the ProxyPreserveHost directive set to "on". The vulnerability is classified as CWE-617, which corresponds to a reachable assertion flaw. In this context, an assertion failure occurs within the mod_proxy_http2 module when processing requests from untrusted clients. This assertion failure can be deliberately triggered by an attacker, causing the Apache HTTP Server process to terminate unexpectedly, resulting in a denial of service (DoS). The vulnerability does not impact confidentiality or integrity but directly affects availability by crashing the server. The CVSS v3.1 base score is 7.5, reflecting a high severity due to the 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), and high impact on availability (A:H). No known exploits are reported in the wild as of the publication date, and no patches are linked yet. The vulnerability is triggered only under specific proxy configurations involving HTTP/2 backends and ProxyPreserveHost enabled, which limits the attack surface but still poses a significant risk to affected deployments.

For European organizations, this vulnerability can lead to service disruptions in web infrastructure relying on Apache HTTP Server as a reverse proxy to HTTP/2 backends with the specified configuration. Such disruptions could affect critical public-facing services, internal applications, or cloud-hosted environments. The denial of service could be exploited by attackers to cause downtime, impacting business continuity, customer trust, and potentially leading to financial losses. Sectors with high reliance on web services, such as finance, government, healthcare, and e-commerce, are particularly vulnerable. Additionally, the ease of exploitation (no authentication or user interaction required) increases the risk of automated attacks from external threat actors. Given the widespread use of Apache HTTP Server in Europe, especially in enterprise and public sector environments, the potential for disruption is significant if mitigations are not applied promptly.

1. Immediate mitigation involves reviewing and modifying Apache HTTP Server configurations to disable ProxyPreserveHost or avoid using HTTP/2 backends in reverse proxy setups until a patch is available. 2. Implement strict access controls and network-level filtering to restrict untrusted client access to proxy endpoints, reducing exposure to potential attackers. 3. Monitor server logs and set up alerts for abnormal crashes or assertion failures in mod_proxy_http2 to detect exploitation attempts early. 4. Stay updated with Apache Software Foundation advisories and apply official patches as soon as they are released. 5. Consider deploying redundant proxy servers or load balancers to maintain service availability during potential DoS events. 6. Conduct internal audits of proxy configurations across all environments to identify and remediate vulnerable setups proactively. 7. Employ Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) capable of detecting and blocking malformed HTTP/2 requests targeting this vulnerability.