CVE-2023-44487 is a high-severity vulnerability affecting the HTTP/2 protocol, specifically related to how request cancellations are handled. HTTP/2 allows clients to cancel requests, which results in resetting streams on the server side. This vulnerability arises because an attacker can rapidly send many request cancellations, causing the server to reset numerous streams in quick succession. This behavior leads to excessive consumption of server resources, effectively resulting in a denial of service (DoS) condition. The vulnerability is categorized under CWE-400, which pertains to uncontrolled resource consumption. Although the exact affected products or versions are not specified, the issue lies within the HTTP/2 protocol implementation itself, which is widely used in modern web servers and applications. The CVSS v3.1 score is 7.5, indicating a high severity with network attack vector, low attack complexity, no privileges required, no user interaction, and impact limited to availability (no confidentiality or integrity impact). The vulnerability was actively exploited in the wild between August and October 2023, demonstrating its practical risk. No patches or vendor-specific mitigations are currently listed, which suggests that affected organizations need to rely on configuration changes or network-level protections until official fixes are available.

For European organizations, this vulnerability poses a significant risk to the availability of web services that rely on HTTP/2. Given the widespread adoption of HTTP/2 in European enterprises, government agencies, and critical infrastructure providers, exploitation could lead to service outages, degraded performance, and potential disruption of business operations. Sectors such as finance, healthcare, telecommunications, and public administration are particularly vulnerable due to their reliance on high-availability web services. The denial of service could also be leveraged as part of a larger attack campaign to distract or disable defenses while other attacks are conducted. Additionally, the lack of required authentication or user interaction means that attackers can exploit this vulnerability remotely and anonymously, increasing the threat surface. The impact is primarily on availability, but prolonged outages could indirectly affect confidentiality and integrity by forcing fallback to less secure systems or emergency procedures.

Given the absence of vendor patches, European organizations should implement specific mitigations to reduce the risk of exploitation. These include: 1) Deploying Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) capable of detecting and throttling abnormal HTTP/2 stream reset patterns to block or rate-limit suspicious traffic. 2) Configuring HTTP/2 server implementations to limit the number of concurrent streams and the rate of stream resets per client IP to prevent resource exhaustion. 3) Employing network-level rate limiting and anomaly detection to identify and mitigate rapid cancellation attacks. 4) Monitoring server logs and network traffic for unusual spikes in HTTP/2 stream resets or cancellations. 5) Considering temporary disabling or downgrading to HTTP/1.1 on critical systems if mitigation controls are insufficient and the risk is high. 6) Keeping abreast of vendor advisories for patches or updates addressing this vulnerability and applying them promptly once available. 7) Conducting regular resilience testing and incident response drills to prepare for potential DoS scenarios.