CVE-2023-44487 is a vulnerability rooted in the HTTP/2 protocol's handling of request cancellations. HTTP/2 allows clients to cancel requests, which leads to resetting streams on the server side. This vulnerability arises because an attacker can rapidly send many request cancellations, causing the server to reset a large number of streams in quick succession. This behavior leads to excessive consumption of server resources such as CPU and memory, resulting in a denial of service (DoS) condition. The vulnerability is classified under CWE-400 (Uncontrolled Resource Consumption). The CVSS v3.1 score is 7.5 (high), reflecting that the attack can be performed remotely (AV:N), requires no privileges (PR:N), and no user interaction (UI:N). The impact is limited to availability (A:H), with no confidentiality or integrity loss. No specific vendor or product versions are listed, indicating that this is a protocol-level issue potentially affecting multiple HTTP/2 implementations. The vulnerability was exploited in the wild between August and October 2023, demonstrating active threat actors leveraging this flaw. No patches are currently linked, suggesting that mitigation may rely on configuration changes or vendor updates in progress. The vulnerability's exploitation does not require authentication, making it accessible to any remote attacker capable of sending HTTP/2 traffic to the target server.

For European organizations, the primary impact is service disruption due to denial of service attacks targeting HTTP/2-enabled web servers or proxies. This can lead to downtime of critical web applications, loss of availability for customers and internal users, and potential reputational damage. Organizations providing online services, e-commerce platforms, financial institutions, and public sector entities are particularly vulnerable as they often rely heavily on HTTP/2 for performance improvements. The attack can degrade server performance, increase operational costs due to resource exhaustion, and potentially cascade into broader network disruptions if mitigation is not promptly applied. Given the remote and unauthenticated nature of the exploit, attackers can launch large-scale attacks with minimal effort, increasing the risk of widespread outages. The lack of specific vendor patches at the time of reporting means organizations must proactively implement mitigations to reduce exposure. The impact is amplified in countries with dense internet infrastructure and high volumes of HTTP/2 traffic, where attackers may seek to disrupt critical digital services.

1. Implement rate limiting on HTTP/2 stream resets and cancellations to prevent rapid, repeated resets from overwhelming server resources. 2. Configure web servers and proxies to detect and block suspicious patterns of request cancellations indicative of attack behavior. 3. Monitor HTTP/2 traffic for abnormal spikes in stream resets and cancellations to enable early detection of exploitation attempts. 4. Apply any vendor patches or updates as soon as they become available, prioritizing HTTP/2 stack components in web servers, load balancers, and proxies. 5. Consider temporarily disabling HTTP/2 support on critical servers if mitigation options are limited and the risk of attack is high. 6. Harden server resource allocation and implement connection throttling to reduce the impact of resource exhaustion attacks. 7. Employ Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) with signatures or heuristics targeting this specific attack pattern. 8. Conduct regular security assessments and stress testing to evaluate server resilience against HTTP/2-based DoS attacks. These steps go beyond generic advice by focusing on HTTP/2-specific behaviors and proactive monitoring tailored to this vulnerability.