Apache has a serious vulnerability, and the HTTP/2 service may be subject to remote code execution

A serious security vulnerability has been found in the open-source server software Apache HTTP Server. Attackers can exploit this vulnerability to corrupt server memory by crafting requests when they have access to the affected service, allowing them to execute code with the privileges of the web service process. The vulnerability is located in the HTTP/2 module, and attackers can trigger a concurrent synchronization flaw without authentication, leading to heap memory corruption. If successfully exploited, it allows code execution with the privileges of the Apache worker process and access to data that the process can read.

The affected range includes Apache HTTP Server versions 2.4.55 to 2.4.70, as well as mod_h2 versions 2.0.8 to 2.0.42 used separately from GitHub. Red Hat stated that the risk involves servers that enable HTTP/2 through the Protocols directive, including H2 for encrypted connections and H2C for plaintext connections. Administrators need to check both global configurations and individual virtual host configurations; if a CDN or reverse proxy is deployed on the website frontend, it is also necessary to check whether the Apache origin server can be accessed directly via HTTP/2.

Apache released HTTP Server 2.4.71 on November 11, 2026, and it is recommended that websites using Apache upgrade immediately. If an upgrade cannot be performed temporarily, HTTP/2 can be disabled as a temporary measure. The issue lies in the assign_headers() function of mod_http2. HTTP/2 allows multiple requests to be processed concurrently over the same connection, and the affected code has a synchronization flaw when handling shared resources, which may lead to heap memory corruption. This vulnerability was discovered by the Anthropic OSS Scanner open-source project and the Google Cloud vulnerability research team. Anthropic reported it to the Apache Foundation on October 26, and the Google Cloud team reported the same vulnerability on November 3.