Critical CVE-2026-23918 Apache HTTP/2 flaw enables DoS, RCE

Affected Environment
Internet-facing Apache HTTP Server 2.4.66 deployments using the HTTP/2 module (mod_http2) are directly exposed. Any organisation relying on Apache for public web services should assume potential impact and verify deployed versions.

Threat Overview
CVE-2026-23918 is a critical double-free flaw in Apache HTTP/2 handling that can cause process crashes and service outages. Under specific memory conditions, the same flaw may allow remote code execution in the web server context, leading to compromise.

Exposure Timeline
The vulnerability and fixed Apache HTTP Server version 2.4.67 were disclosed on 2026-05-06 in vendor security notes. Exposure persists on any systems still running 2.4.66 with HTTP/2 enabled until patching or effective mitigation is applied.

Attack Surface
The main attack surface is publicly reachable Apache sites using HTTP/2 where mod_http2 is enabled by default or configuration. Remote, unauthenticated attackers can send crafted HTTP/2 requests to reachable services, making broad scanning feasible.

Technical Root Cause
A double-free memory corruption bug exists in HTTP/2 stream handling logic within Apache HTTP Server 2.4.66. Improper memory management allows repeated deallocation of the same memory, creating conditions for crashes or code execution.

Exploitation Pathway
An attacker sends specially crafted HTTP/2 requests to trigger the double-free in the mod_http2 processing pipeline. This can reliably cause denial-of-service, and in certain memory layouts may be leveraged to execute arbitrary code on the server.