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Apache has patched CVE-2026-23918, a critical flaw in Apache HTTP Server’s HTTP/2 handling that Apache describes as a “double free and possible RCE.” The issue affects Apache HTTP Server 2.4.66 and was fixed in 2.4.67, released on May 4, 2026.
The CVE-2026-23918 vulnerability matters because it can be abused remotely and without authentication. Public reporting says the bug can cause a denial-of-service condition and, under certain conditions, may also open a path to remote code execution, making it one of the most serious issues addressed in Apache’s latest security release.
Apache credits Bartlomiej Dmitruk of striga.ai and Stanislaw Strzalkowski of isec.pl with reporting the flaw. Apache’s own vulnerability page shows it was reported to the security team on December 10, 2025, fixed in source on December 11, 2025, and shipped to users in the 2.4.67 release months later.
CVE-2026-23918 analysis
According to Apache and researcher commentary cited by The Hacker News, the bug is a double-free in mod_http2, specifically in the stream cleanup path. It can be triggered when a client sends an HTTP/2 HEADERS frame and then immediately sends RST_STREAM with a non-zero error code before the stream is fully registered by the multiplexer.
That sequence can cause two callbacks to run in a way that pushes the same stream object into the cleanup array twice. When Apache later destroys the stream entries, memory that has already been freed gets released again. In practical terms, the vulnerability in CVE-2026-23918 is a memory-management flaw that can crash worker processes and, in the right environment, be shaped into code execution.
The denial-of-service path appears to be the easiest outcome. The researchers told The Hacker News that one TCP connection and two HTTP/2 frames are enough to crash a worker in default deployments that use mod_http2 with a multi-threaded MPM. They also noted that MPM prefork is not affected, while the possible RCE path depends on an APR configuration using the mmap allocator, which is said to be the default on Debian-derived systems and in the official httpd Docker image.
As for exploitation maturity, public reporting says the researchers built a working CVE-2026-23918 poc for x86_64 in lab conditions. They also said practical exploitation still needs helpful conditions such as an information leak and favorable memory reuse, so code execution is more demanding than simple service disruption.
At this stage, public details for CVE-2026-23918 point much more clearly to process crashes and worker instability than to widely reproducible RCE in the field. There are also no vendor-published CVE-2026-23918 iocs, so defenders should focus on version exposure, unexpected worker crashes, and suspicious HTTP/2 reset patterns rather than on a stable signature set.
CVE-2026-23918 Mitigation
The core fix is to upgrade Apache HTTP Server from 2.4.66 to 2.4.67. Apache’s security advisory explicitly recommends moving to the patched version, and SecurityWeek notes that the release fixes 11 vulnerabilities, including this critical HTTP/2 issue.
For immediate triage, defenders should identify internet-facing systems where mod_http2 is enabled and where threaded MPMs are in use. That is the most practical way to detect CVE-2026-23918 exposure because the attack hinges on HTTP/2 request handling, not on a dropped malware artifact or traditional post-exploitation beacon.
If emergency patching is delayed, reducing exposure to HTTP/2 traffic may help shrink the attack surface until updates are applied. The CVE-2026-23918 payload described publicly is not a conventional file or binary but a crafted sequence of HTTP/2 frames designed to force the faulty cleanup path, so network-facing Apache instances should be prioritized first.
From a risk perspective, CVE-2026-23918 affects organizations that rely on Apache HTTP Server 2.4.66 for public web workloads, especially where HTTP/2 is enabled by default or broadly deployed for performance reasons. That includes standard Linux-based web servers as well as containerized deployments using the official Apache image.
FAQ
What is CVE-2026-23918 and how does it work?
It is a critical double-free flaw in Apache HTTP Server’s HTTP/2 handling. A specially timed sequence of HTTP/2 frames can push the same stream object into cleanup twice, leading to worker crashes and potentially enabling remote code execution under favorable conditions.
When was CVE-2026-23918 first discovered?
Apache’s vulnerability page says the issue was reported to the security team on December 10, 2025. The fix landed in source on December 11, 2025, and the patched 2.4.67 release was published on May 4, 2026.
What is the impact of CVE-2026-23918 on systems?
The most immediate impact is denial of service through crashed Apache workers. Public reporting also says the flaw may allow remote code execution, although that path appears more complex and environment-dependent than the crash scenario.
Can CVE-2026-23918 still affect me in 2026?
Yes. Systems can still be exposed in 2026 if they are running Apache HTTP Server 2.4.66 with mod_http2 enabled and have not yet been updated to 2.4.67. The risk is especially relevant for deployments using threaded MPMs.
How can I protect myself from CVE-2026-23918?
Upgrade to Apache HTTP Server 2.4.67 as soon as possible, identify exposed HTTP/2-enabled deployments, and prioritize externally reachable servers for remediation. Where patching cannot happen immediately, reducing HTTP/2 exposure can help lower short-term risk.
