CVE-2025-49630 is a reachable assertion vulnerability (CWE-617) in the Apache HTTP Server's mod_proxy_http2 module affecting versions 2.4.26 through 2.4.63. The flaw manifests when Apache is configured as a reverse proxy forwarding requests to an HTTP/2 backend server, with the ProxyPreserveHost directive enabled (set to "on"). Under these conditions, specially crafted requests from untrusted clients can trigger an assertion failure within the mod_proxy_http2 code path. This assertion failure causes the Apache HTTP Server process to terminate unexpectedly, resulting in a denial of service (DoS) condition. The vulnerability does not impact confidentiality or integrity but severely affects availability by crashing the server. Exploitation requires no privileges or user interaction and can be performed remotely over the network. The CVSS v3.1 base score is 7.5, reflecting high severity due to network attack vector, low attack complexity, no privileges required, and no user interaction needed. No public exploits have been reported yet, but the vulnerability is publicly disclosed and should be considered a significant risk for affected deployments. The vulnerability is particularly relevant for environments using Apache as a reverse proxy to HTTP/2 backend services with ProxyPreserveHost enabled, a configuration common in modern web infrastructures aiming to preserve the original host header for backend routing or logging purposes.

For European organizations, this vulnerability poses a significant risk to service availability, especially for public-facing web services relying on Apache HTTP Server as a reverse proxy to HTTP/2 backends. A successful attack can cause server crashes, leading to downtime and potential disruption of critical business or government services. This can impact customer trust, operational continuity, and potentially lead to financial losses. Sectors such as finance, healthcare, government, and telecommunications, which often deploy Apache HTTP Server in proxy roles, are particularly vulnerable. Additionally, the ease of exploitation and lack of required authentication increase the likelihood of opportunistic attacks. Organizations with high traffic volumes or those relying on high availability SLAs may experience amplified operational impacts. While confidentiality and integrity are not directly affected, the denial of service can indirectly affect business processes and incident response resources.

Immediate mitigation steps include reviewing Apache HTTP Server configurations to identify if ProxyPreserveHost is set to "on" in reverse proxy setups to HTTP/2 backends. If feasible, temporarily disable ProxyPreserveHost or disable HTTP/2 proxying until a patched version is available. Monitor Apache HTTP Server releases closely for patches addressing CVE-2025-49630 and apply updates promptly once released. Employ network-level protections such as rate limiting and web application firewalls (WAFs) to detect and block suspicious traffic patterns targeting mod_proxy_http2. Implement robust monitoring and alerting on Apache server crashes or restarts to enable rapid incident response. Consider deploying redundant proxy servers or load balancers to minimize service disruption during potential attacks. Conduct internal audits of proxy configurations to ensure adherence to security best practices and minimize exposure. Engage with vendors or managed service providers to confirm patch timelines and mitigation support.