CVE-2018-1000168 is a high-severity vulnerability affecting the nghttp2 library versions from 1.10.0 up to and including 1.31.0. The vulnerability arises from improper input validation (CWE-20) in the handling of ALTSVC frames within the HTTP/2 protocol implementation. Specifically, malformed ALTSVC frames can trigger a segmentation fault due to a null pointer dereference (CWE-476), leading to a denial of service (DoS) condition. This vulnerability can be exploited remotely by an unauthenticated attacker over the network, as no privileges or user interaction are required. The flaw is triggered when a client processes a malicious ALTSVC frame, causing the application using the vulnerable nghttp2 library to crash. The issue was addressed and fixed in version 1.31.1 of nghttp2. Given the CVSS v3.1 base score of 7.5 (high), the vulnerability poses a significant risk to services relying on vulnerable versions of nghttp2, especially those exposing HTTP/2 endpoints to untrusted networks. Although no known exploits are reported in the wild, the ease of exploitation and potential for service disruption make this a critical patching priority for affected systems.

For European organizations, the impact of this vulnerability primarily involves service availability. Organizations using nghttp2 in their HTTP/2 implementations—such as web servers, proxies, or client applications—may experience denial of service attacks that disrupt normal operations. This can lead to downtime, degraded user experience, and potential loss of business continuity. Sectors with high reliance on web services, including finance, government, healthcare, and e-commerce, could face operational disruptions. Additionally, denial of service incidents may have regulatory implications under the EU's NIS Directive, which mandates security and availability of essential services. While confidentiality and integrity are not directly impacted, the availability impact can indirectly affect trust and reputation. The vulnerability's network-exploitable nature means attackers can launch DoS attacks remotely without authentication, increasing the threat surface for organizations with public-facing HTTP/2 services.

European organizations should immediately verify whether their infrastructure uses nghttp2 versions between 1.10.0 and 1.31.0. If so, upgrading to version 1.31.1 or later is essential to remediate the vulnerability. Organizations should audit all software components and dependencies that incorporate nghttp2, including web servers, reverse proxies, HTTP/2 clients, and embedded systems. Where immediate patching is not feasible, implementing network-level mitigations such as rate limiting, deep packet inspection, or firewall rules to detect and block malformed ALTSVC frames can reduce exposure. Monitoring application logs for crashes or segmentation faults related to HTTP/2 traffic can help detect exploitation attempts. Additionally, organizations should ensure robust incident response plans are in place to quickly address potential denial of service events. Regular vulnerability scanning and dependency management practices should be enforced to prevent similar issues.