Full Report
A vulnerability has been discovered in Apache HTTP Server with the HTTP/2 protocol that could allow for remote code execution. Apache is a free, open-source web server software that enables the delivery of web content over the internet. Successful exploitation could result in denial of service, crashing worker processes with minimal effort. In certain setups, especially those using APR with mmap (common on Debian systems and official Docker images), it may also be exploited for remote code execution.
Analysis Summary
# Vulnerability: Apache HTTP Server mod_http2 Double-Free RCE
## CVE Details
- **CVE ID:** CVE-2026-23918
- **CVSS Score:** Not explicitly listed in the source, but categorized as **High** risk for government and business entities.
- **CWE:** Double-Free (CWE-415)
## Affected Systems
- **Products:** Apache HTTP Server
- **Versions:** All versions prior to 2.4.67
- **Configurations:** Systems running the `mod_http2` module. Risk is elevated to Remote Code Execution (RCE) in setups using **APR (Apache Portable Runtime) with mmap**, which is standard in:
- Debian-based Linux distributions
- Official Apache Docker images
## Vulnerability Description
CVE-2026-23918 is a **double-free memory corruption flaw** located within the `mod_http2` module of Apache HTTP Server 2.4.66. The vulnerability is triggered when a specially crafted sequence of HTTP/2 requests causes the server to attempt to clean up the same data stream twice. This memory mismanagement can lead to immediate crashes of worker processes (Denial of Service) or, under specific memory mapping configurations, allow an attacker to execute arbitrary code with the privileges of the web server process.
## Exploitation
- **Status:** PoC (Proof of Concept) code currently exists for both Denial of Service (DoS) and Remote Code Execution (RCE).
- **Complexity:** Low (minimal effort required for DoS; RCE potential varies by environment).
- **Attack Vector:** Network (Remote)
## Impact
- **Confidentiality:** High (Potential for RCE)
- **Integrity:** High (Potential for RCE)
- **Availability:** High (Worker process crashing/DoS)
## Remediation
### Patches
- **Upgrade to Apache HTTP Server version 2.4.67** or later.
### Workarounds
- If patching is not immediately possible, disable the HTTP/2 protocol by removing `h2` and `h2c` from the `Protocols` configuration in `httpd.conf`.
- Enable anti-exploitation features such as Data Execution Prevention (DEP) or Address Space Layout Randomization (ASLR) at the OS level to hinder RCE attempts.
## Detection
- **Indicators of Compromise:** Unusual spikes in Apache worker process crashes (segmentation faults) or unexpected memory usage patterns.
- **Detection Methods and Tools:**
- Perform automated vulnerability scans using SCAP-compliant tools.
- Monitor web server logs for irregular HTTP/2 stream sequences.
- Conduct external penetration testing to verify susceptibility.
## References
- **Vendor Advisory:** hxxps[://]httpd[.]apache[.]org/security/vulnerabilities_24[.]html
- **CVE Record:** hxxps[://]www[.]cve[.]org/CVERecord?id=CVE-2026-23918
- **Security Analysis:** hxxps[://]securityaffairs[.]com/191759/security/apache-fixes-critical-http-2-double-free-flaw-cve-2026-23918-enabling-rce[.]html