Apache HTTP Server 2.4.67 Patches HTTP/2 Double-Free RCE Risk and Multiple Web Server Flaws
Apache HTTP Server is not just another web service sitting in the background. It is still core internet plumbing, which means a memory-safety flaw in its HTTP/2 handling deserves immediate attention from defenders.
The Apache Software Foundation has released Apache HTTP Server 2.4.67, a security update published on May 4, 2026, to address CVE-2026-23918 and several other vulnerabilities across the server’s HTTP/2, proxy, authentication, WebDAV, and module-handling components.
The most serious issue is CVE-2026-23918, described by Apache as a double-free vulnerability in Apache HTTP Server’s HTTP/2 protocol handling. Apache says the flaw affects version 2.4.66 and may lead to possible remote code execution. The fix is included in version 2.4.67.
What Happened
Apache HTTP Server 2.4.67 patches a set of newly disclosed flaws, with CVE-2026-23918 standing out because of its potential impact and its location in HTTP/2 handling. A double-free bug occurs when software attempts to free the same memory region more than once. In network-facing software, that class of bug can create instability, denial-of-service conditions, or, in more dangerous cases, memory corruption that may be shaped into code execution.
Apache’s advisory describes CVE-2026-23918 as “Double Free and possible RCE” in the HTTP/2 protocol. The issue is tied to an early reset condition and affects Apache HTTP Server 2.4.66. Users are advised to upgrade to 2.4.67.
The release is broader than a single HTTP/2 fix. Apache’s security page also lists additional vulnerabilities fixed in 2.4.67, including issues in mod_rewrite, mod_proxy_ajp, mod_md, mod_dav_lock, mod_auth_digest, mod_authn_socache, and HTTP response handling across multiple modules.
The Vulnerabilities Fixed in 2.4.67
The key issue for most defenders is CVE-2026-23918, the HTTP/2 double-free flaw. Because Apache HTTP Server is commonly deployed on internet-facing systems, even a version-specific RCE possibility can create urgent patch pressure once details become public.
Apache also fixed CVE-2026-24072, a mod_rewrite privilege escalation issue involving ap_expr. According to Apache, the flaw affects Apache HTTP Server 2.4.66 and earlier and could allow local .htaccess authors to read files with the privileges of the httpd user.
Several fixes affect mod_proxy_ajp, including CVE-2026-28780, CVE-2026-33857, CVE-2026-34032, and CVE-2026-34059. These cover heap-based buffer overflow, out-of-bounds read, missing null-termination checks, heap over-read, and possible memory disclosure scenarios involving AJP proxy handling.
Other patched issues include CVE-2026-29168 in mod_md, involving unrestricted OCSP response resource allocation; CVE-2026-29169 in mod_dav_lock, which may allow a crash through a malicious request; CVE-2026-33006, a timing attack against mod_auth_digest that Apache says may allow Digest authentication bypass; CVE-2026-33007, a mod_authn_socache crash issue in caching forward proxy configurations; and CVE-2026-33523, an HTTP response splitting flaw involving untrusted or compromised backend servers.
Why This Stands Out
The dangerous part of this release is not just the number of CVEs. It is the mix of attack surfaces.
HTTP/2 sits directly on the request path. Authentication modules influence access control. Proxy modules sit between front-end clients and backend services. WebDAV and OCSP-related components may be less universally enabled, but they still matter in environments where Apache is heavily extended through modules.
That makes the 2.4.67 update a priority not only for public web servers, but also for reverse proxies, internal application gateways, legacy hosting platforms, developer environments, and appliances that bundle Apache HTTP Server under the hood.
The HTTP/2 flaw is especially important because modern web stacks often enable HTTP/2 for performance without treating it as a separate security surface. Protocol-level features such as stream resets, multiplexing, and connection state management can expose bugs that are not visible in simpler HTTP/1.1 request flows.
Operational Risk for Defenders
Defenders should treat the Apache advisory as a patch-and-verify event, not just a package upgrade notice.
The first step is to identify Apache HTTP Server versions across internet-facing and internal assets. Systems running Apache HTTP Server 2.4.66 should receive immediate attention because CVE-2026-23918 is specifically listed against that version. Systems running 2.4.66 or earlier may also be exposed to the wider set of flaws fixed in 2.4.67, depending on enabled modules and configuration.
Administrators should pay particular attention to servers with HTTP/2 enabled, reverse proxy deployments using AJP, configurations that allow .htaccess authors to influence rewrite behavior, Digest authentication deployments, caching forward proxy configurations, and environments where mod_dav_lock or mod_md are enabled.
Where immediate patching is delayed, defenders should reduce exposed attack surface by disabling unnecessary modules, reviewing HTTP/2 exposure, restricting administrative access, and monitoring for unusual crashes, authentication anomalies, malformed HTTP/2 traffic, and suspicious proxy behavior. These are temporary controls, not replacements for the 2.4.67 upgrade.
Bigger Picture
This release is another reminder that mature infrastructure does not mean low-risk infrastructure. Apache HTTP Server has decades of operational history, but its deployment footprint and module ecosystem make every serious flaw consequential.
The risk is also amplified by asset visibility gaps. Many organizations know which public domains they run, but not always which embedded systems, internal tools, packaged applications, lab systems, or legacy virtual machines still expose Apache HTTP Server. That gap is where patch urgency often turns into incident response.
For security teams, the practical question is not whether Apache is “in use.” It almost certainly is somewhere. The question is whether every instance is visible, versioned, owned, and patched.
NeuraCyb's Assessment
CVE-2026-23918 should be handled as a high-priority infrastructure flaw because it combines a memory-safety bug, HTTP/2 exposure, and possible RCE language in one of the internet’s most widely deployed web servers. The broader 2.4.67 release also closes multiple secondary paths involving proxying, authentication, response handling, and denial-of-service conditions.
The strongest defensive move is straightforward: inventory Apache HTTP Server assets, prioritize exposed HTTP/2 and proxy deployments, upgrade to 2.4.67, and confirm that unnecessary modules are not quietly expanding the attack surface. The teams that move fastest will not be the ones with the longest patch policy; they will be the ones that already know where Apache is running.
References
Apache HTTP Server 2.4 Vulnerabilities - Apache Software Foundation
