CVE-2025-49630 is a vulnerability identified in the Apache HTTP Server, specifically affecting versions 2.4.26 through 2.4.63. The issue arises in the mod_proxy_http2 module when the server is configured as a reverse proxy to an HTTP/2 backend with the ProxyPreserveHost directive set to "on." Under these conditions, untrusted clients can trigger a reachable assertion failure, classified under CWE-617 (Reachable Assertion). This means that the server performs an assertion check that can be deliberately failed by crafted input, leading to a denial of service (DoS) condition. The assertion failure causes the Apache HTTP Server process to terminate unexpectedly, disrupting service availability. The vulnerability does not require authentication, and exploitation can be performed remotely by sending malicious requests to the affected proxy configuration. Although no known exploits are currently reported in the wild, the vulnerability's nature and the widespread use of Apache HTTP Server in proxy roles make it a significant concern. The absence of a CVSS score indicates that the vulnerability is newly published and pending further evaluation. The vulnerability is technical in nature and specific to configurations involving HTTP/2 backend proxies with ProxyPreserveHost enabled, which is a common setup in modern web infrastructure to maintain host headers for backend services.

For European organizations, this vulnerability poses a risk primarily to web infrastructure relying on Apache HTTP Server as a reverse proxy to HTTP/2 backends with ProxyPreserveHost enabled. The impact is a denial of service, which can lead to service outages, degraded user experience, and potential disruption of critical business operations, especially for organizations providing web services or APIs. This could affect sectors such as finance, government, healthcare, and e-commerce, where high availability and reliability of web services are essential. Additionally, denial of service attacks can be leveraged as part of larger multi-vector attacks or to distract security teams while other attacks are conducted. Given the reliance on Apache HTTP Server across many European enterprises and public sector entities, the vulnerability could lead to significant operational disruptions if exploited. The lack of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, as attackers may develop exploits following public disclosure.

To mitigate this vulnerability, European organizations should first identify if their Apache HTTP Server instances are configured as reverse proxies to HTTP/2 backends with ProxyPreserveHost set to "on." Immediate steps include: 1) Temporarily disabling ProxyPreserveHost or modifying the proxy configuration to avoid the vulnerable setup until a patch is available. 2) Monitoring Apache HTTP Server logs for unusual assertion failures or crashes related to mod_proxy_http2. 3) Implementing rate limiting and filtering on incoming requests to reduce exposure to malicious traffic targeting this vulnerability. 4) Applying strict network segmentation and access controls to limit exposure of proxy servers to untrusted clients. 5) Staying updated with Apache Software Foundation announcements for patches or updates addressing this issue and applying them promptly once released. 6) Conducting thorough testing of proxy configurations in staging environments to verify that changes do not impact legitimate traffic. These steps go beyond generic advice by focusing on configuration auditing, proactive monitoring, and network-level protections tailored to the vulnerability's characteristics.