CVE-2026-44631: Apache HTTP Server Buffer Overflow Flaw

CVE-2026-44631 Overview

CVE-2026-44631 is a buffer underwrite vulnerability in Apache HTTP Server triggered by crafted regular expressions in the configuration. The flaw affects Apache HTTP Server versions 2.4.0 through 2.4.67 and is fixed in 2.4.68. The vulnerability is classified under CWE-124: Buffer Underwrite ('Buffer Underflow') and carries a network attack vector with no required privileges or user interaction. Administrators running affected versions should upgrade immediately to prevent potential memory corruption and code execution scenarios.

Critical Impact
A remote attacker can leverage crafted regular expressions processed by Apache HTTP Server configuration handling to corrupt memory, potentially leading to denial of service or arbitrary code execution.

Affected Products

Apache HTTP Server 2.4.0 through 2.4.67
Deployments using regular expressions in httpd.conf directives
All operating system platforms running affected httpd versions

Discovery Timeline

2026-06-08 - CVE-2026-44631 published to NVD
2026-06-11 - Last updated in NVD database

Technical Details for CVE-2026-44631

Vulnerability Analysis

The vulnerability resides in how Apache HTTP Server processes regular expressions defined in its configuration. A buffer underwrite occurs when the server writes data before the start of an allocated buffer. This memory corruption primitive can overwrite adjacent process memory, including heap metadata or function pointers. The flaw is reachable over the network, meaning an attacker who can influence regex-based directives or trigger their evaluation may corrupt server state without authentication. Successful exploitation can compromise confidentiality, integrity, and availability of the web server process.

Root Cause

The root cause is improper boundary handling during regex compilation or matching in Apache HTTP Server prior to version 2.4.68. The code path writes to memory locations preceding the allocated buffer when processing specifically crafted regular expression patterns, violating safe memory access boundaries as described by CWE-124.

Attack Vector

Exploitation requires that a crafted regular expression be processed by the server configuration. An attacker who can inject configuration content, influence virtual host configuration, or trigger regex evaluation via request data targeting vulnerable directives can drive the underwrite condition. No user interaction or prior authentication is required for the network-accessible attack path.

No verified public proof-of-concept code is currently available. Refer to the Apache HTTPD Vulnerabilities List and the Openwall OSS-Security Discussion for technical context.

Detection Methods for CVE-2026-44631

Indicators of Compromise

Unexpected httpd worker crashes or segmentation faults logged in system journals
Anomalous child process restarts or core dumps in the Apache process tree
Configuration files containing unusual or attacker-supplied regular expression patterns in directives such as LocationMatch, DirectoryMatch, or RewriteRule

Detection Strategies

Inventory all Apache HTTP Server instances and identify any running versions 2.4.0 through 2.4.67
Audit httpd.conf and included configuration files for regex-based directives that accept untrusted input
Monitor for abnormal memory faults associated with httpd processes using OS-level crash reporting

Monitoring Recommendations

Enable verbose error logging in Apache and forward logs to a centralized SIEM for correlation
Alert on repeated httpd worker terminations or signal 11 events on web-facing hosts
Track configuration file changes through file integrity monitoring to detect injected regex patterns

How to Mitigate CVE-2026-44631

Immediate Actions Required

Upgrade Apache HTTP Server to version 2.4.68 or later on all affected hosts
Identify and validate all regex-based configuration directives before reloading httpd
Restrict write access to Apache configuration files to trusted administrators only

Patch Information

The Apache Software Foundation has released Apache HTTP Server 2.4.68, which remediates CVE-2026-44631. Administrators should obtain the update from the official Apache HTTPD Vulnerabilities List and apply it across all affected deployments. Restart the httpd service after upgrading to ensure the patched binary is active.

Workarounds

If immediate patching is not possible, remove or simplify regex-based directives in configuration files
Restrict network exposure of affected httpd instances using firewall rules or reverse proxies until upgrade completes
Apply strict file permissions on configuration files to prevent unauthorized modification of regex patterns

bash

# Verify installed Apache HTTP Server version
httpd -v

# Example upgrade on Debian/Ubuntu
sudo apt-get update && sudo apt-get install --only-upgrade apache2

# Example upgrade on RHEL/CentOS
sudo yum update httpd

# Restart service after upgrade
sudo systemctl restart httpd