CVE-2024-23327 is a high-severity vulnerability affecting Envoy Proxy, a widely used high-performance edge, middle, and service proxy. The vulnerability is a NULL pointer dereference (CWE-476) that occurs when Proxy Protocol version 2 (PPv2) is enabled both on a listener and a subsequent cluster. Specifically, the Envoy instance will experience a segmentation fault (crash) when attempting to craft the upstream PPv2 header if the downstream request has a command type of LOCAL and lacks the protocol block. This results in the proxy process crashing, causing a denial of service (DoS) condition. The issue affects multiple versions of Envoy, including all versions from 1.26.0 up to but not including patched releases 1.26.7, 1.27.3, 1.28.1, and 1.29.1. The vulnerability requires no privileges or user interaction to exploit and can be triggered remotely by sending crafted requests that meet the conditions described. There are currently no known exploits in the wild, and no workarounds exist other than upgrading to a fixed version. The CVSS v3.1 base score is 7.5 (high), reflecting the network attack vector, low complexity, no privileges required, no user interaction, and an impact limited to availability (service crash).

For European organizations, the impact of this vulnerability can be significant, especially for those relying on Envoy Proxy as a critical component in their infrastructure, such as cloud providers, telecom operators, financial institutions, and large enterprises using service mesh architectures or edge proxies. A successful exploitation leads to a denial of service by crashing the Envoy process, potentially disrupting traffic flow, degrading application availability, and causing outages in services dependent on Envoy for load balancing, routing, or security enforcement. This can affect customer-facing applications and internal services, leading to operational downtime and potential financial and reputational damage. Given Envoy's popularity in modern microservices and cloud-native environments, the vulnerability could be exploited to target high-value infrastructure components. The lack of known exploits currently reduces immediate risk, but the ease of triggering the crash and the absence of workarounds necessitate prompt remediation to avoid service disruptions.

The primary and most effective mitigation is to upgrade Envoy Proxy to one of the patched versions: 1.26.7, 1.27.3, 1.28.1, or 1.29.1 or later. Organizations should prioritize this update in their patch management cycles. In environments where immediate upgrade is not feasible, consider temporarily disabling Proxy Protocol v2 on listeners and clusters to prevent the vulnerable code path from being exercised, though this may impact legitimate traffic handling and should be tested carefully. Additionally, implement network-level protections such as filtering or rate limiting traffic that could trigger the vulnerability, especially from untrusted sources. Monitoring Envoy logs and metrics for unexpected crashes or restarts can help detect exploitation attempts. Finally, incorporate this vulnerability into incident response and vulnerability management workflows to ensure timely detection and remediation.