TT-CSIRT – 463.12.11.26- Critical Remote Code Execution Vulnerability in Apache HTTP Server.

A critical vulnerability, CVE-2026-119618, exists in the Apache HTTP Server's HTTP/2 component (modhttp2), which can be exploited to achieve remote code execution. This flaw stems from a race condition within the assignheaders() function of the module, potentially leading to heap memory corruption if synchronization is improper. The vulnerability affects Apache HTTP Server versions 2.4.55 through 2.4.70 when HTTP/2 functionality is active. The Apache Software Foundation released security update Apache HTTP Server 2.4.71 on November 11, 2026, to remediate this issue, and the vulnerability carries a CVSS v3.1 score of 9.8 (Critical) according to Red Hat's assessment.
Affected systems include Apache HTTP Server versions 2.4.55 through 2.4.70, provided the modhttp2 module is loaded and HTTP/2 is enabled. Standalone modh2 versions 2.0.8 through 2.0.42 are also affected. To mitigate the risk, systems must upgrade to Apache HTTP Server 2.4.71 or install the vendor-patched httpd/modhttp2 package. If immediate patching is not feasible, disabling HTTP/2 in the Protocols configuration and reverting to HTTP/1.1 offers a temporary reduction in exposure.

* Vulnerability identifier: CVE-2026-119618.
* Affected component: Apache HTTP Server HTTP/2 component (modhttp2).
* Vulnerability mechanism: Race condition in the assignheaders() function of modhttp2, potentially causing heap memory corruption and remote code execution.
* Affected software versions: Apache HTTP Server versions 2.4.55 through 2.4.70, where HTTP/2 is enabled.
* Remediation release: Apache HTTP Server 2.4.71, released on November 11, 2026.
* CVSS score: 9.8 (Critical), assessed by Red Hat.
* Affected module dependencies: Standalone modh2 versions 2.0.8 through 2.0.42 are also affected.
* Prerequisite for vulnerability: modhttp2 must be loaded and HTTP/2 (h2 or h2c) must be enabled.
* Impact: Remote execution of attacker-controlled code with the privileges of the Apache worker process, unauthorized access to application data, and potential service disruption.
* Affected packages: Linux distribution packages may have fixed versions via vendor backports.

This advisory details a specific software flaw rooted in timing issues within low-level implementation code, demonstrating how subtle synchronization errors can cascade into catastrophic security failures like remote code execution, even in mature server components. The pattern here is the inherent tension between feature enablement (HTTP/2) and secure state management, where adding functionality introduces complexity that threatens core stability. The emphasis on disabling HTTP/2 as a temporary mitigation highlights a systemic failure: relying on complex, feature-rich protocols introduces an attack surface that must be actively managed through strict configuration boundaries, rather than assuming security is inherent.
The narrative structure leans heavily on the necessity of immediate patching, which pushes readers toward a single solution while underscoring the operational reality that system architects often have to choose between security mandates and service availability. The underlying implication is that the complexity introduced by modern protocol features must be weighed against the risk, suggesting that feature-rich systems require rigorous procedural controls (like strict protocol configuration checks) before deployment rather than just patching the resulting flaw.
Bridge Questions: If a system is running older, secure software but has HTTP/2 enabled, what other implicit assumptions about its configuration or patch history might also be vulnerable? What frameworks exist for balancing necessary performance features against the inherent risk of timing-based memory corruption in high-throughput network services?