CVE-2024-30255 is a vulnerability in the Envoy proxy's HTTP/2 codec that allows an attacker to cause CPU exhaustion by sending a flood of CONTINUATION frames without the END_HEADERS bit set. Envoy is widely used as a cloud-native edge and service proxy, handling HTTP/2 traffic. The flaw exists in versions prior to 1.29.3, 1.28.2, 1.27.4, and 1.26.8, where the HTTP/2 protocol stack does not enforce limits on the number of CONTINUATION frames after the header map limits are exceeded. An attacker can exploit this by sending a continuous stream of CONTINUATION frames, which forces Envoy to process excessive header frames, leading to high CPU utilization. The CPU consumption scales roughly at one core per 300Mbit/s of malicious traffic, potentially resulting in denial of service through resource exhaustion. This vulnerability is classified under CWE-390, indicating detection of an error condition without appropriate action, meaning Envoy detects the abnormal frame sequence but fails to mitigate or terminate the connection promptly. No authentication or user interaction is required, and the attack can be launched remotely over the network. There are no known exploits in the wild yet, but the risk remains significant due to the potential impact on availability. The recommended mitigation is to upgrade Envoy to the patched versions 1.29.3, 1.28.2, 1.27.4, or 1.26.8. As a temporary workaround, disabling HTTP/2 for downstream connections can prevent exploitation but may impact performance or functionality. This vulnerability highlights the importance of robust protocol handling and resource management in proxy software.

For European organizations, this vulnerability poses a risk of denial of service attacks targeting critical infrastructure that relies on Envoy proxies for edge routing, service mesh, or API gateway functions. High CPU utilization caused by malicious CONTINUATION frame floods can degrade service availability, leading to downtime or degraded performance of web applications, microservices, and cloud-native platforms. Organizations in sectors such as finance, telecommunications, government, and cloud service providers are particularly vulnerable due to their reliance on scalable and resilient proxy infrastructure. The attack requires no authentication, making public-facing Envoy instances attractive targets. Disruption could affect end-users and business operations, potentially causing financial loss and reputational damage. Additionally, the increased CPU load may lead to higher operational costs due to scaling or emergency incident response. While confidentiality and integrity are not directly impacted, the availability impact alone can be significant, especially for services with strict uptime requirements.

European organizations should immediately assess their Envoy deployments to identify versions affected by CVE-2024-30255. The primary mitigation is to upgrade Envoy to one of the patched versions: 1.29.3, 1.28.2, 1.27.4, or 1.26.8. This ensures the HTTP/2 codec properly limits CONTINUATION frames and prevents CPU exhaustion. If immediate upgrading is not feasible, organizations should consider disabling HTTP/2 protocol support on downstream connections to block the attack vector, understanding this may impact performance or compatibility. Network-level mitigations include deploying rate limiting or anomaly detection on HTTP/2 traffic to identify and block excessive CONTINUATION frames. Monitoring CPU usage patterns on Envoy instances can help detect ongoing exploitation attempts. Additionally, implementing Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) with HTTP/2 protocol awareness can provide further protection. Organizations should also review their incident response plans to handle potential denial of service events related to this vulnerability. Regularly updating and patching Envoy and related infrastructure components remains critical to maintaining security posture.