CVE-2026-44631: 
Apache HTTP Server vulnerability analysis and mitigation

CVE-2026-44631 is a Buffer Underwrite (Buffer Underflow) vulnerability in Apache HTTP Server triggered by crafted regular expressions in the server configuration. It affects Apache HTTP Server versions 2.4.0 through 2.4.67, and was reported on 2026-04-27, fixed in the 2.4.x branch on 2026-06-05, and publicly disclosed with the release of version 2.4.68 on 2026-06-08. The vulnerability carries a CVSS v3.1 base score of 9.8 (Critical), requiring no authentication, privileges, or user interaction (GitHub Advisory, Apache Advisory).

The vulnerability is classified as CWE-124 (Buffer Underwrite / Buffer Underflow) and is rooted in a signed char overflow in the ap_regname function, which processes regular expressions used in Apache HTTP Server configuration (oss-security). When a specially crafted regular expression is supplied in the server configuration, the signed char overflow causes a write to a memory location prior to the beginning of a buffer (heap underflow), potentially enabling arbitrary code execution. The attack vector is network-based with low complexity, and no privileges or user interaction are required. The vulnerability was discovered independently by Zhenpeng (Leo) Lin at depthfirst and Bartlomiej Dmitruk (oss-security).

Successful exploitation of this vulnerability can result in complete compromise of the affected Apache HTTP Server instance, with high impact to confidentiality, integrity, and availability. An unauthenticated remote attacker could achieve arbitrary code execution with the privileges of the web server process, potentially enabling data exfiltration, service disruption, or lateral movement within the hosting environment (GitHub Advisory, Apache Advisory).

As of the time of disclosure, there is no public proof-of-concept exploit and no evidence of active in-the-wild exploitation (Feedly). The EPSS score is approximately 0.505%, placing it in the 39th percentile for exploitation probability within 30 days (GitHub Advisory). No threat actor attribution or CISA KEV catalog listing has been reported at this time. The vulnerability is detectable by Nessus (plugins 319901, 320880) and Qualys scanners.

Apache has released version 2.4.68, which fixes this vulnerability; all users running Apache HTTP Server 2.4.0 through 2.4.67 should upgrade immediately (Apache Advisory). As an interim measure until patching is possible, administrators should restrict write access to Apache configuration files and carefully audit any regular expressions used in the server configuration to prevent introduction of malicious patterns. Monitoring for unexpected configuration changes is also recommended (Feedly).

The vulnerability received coverage from multiple cybersecurity news outlets including CyberSecurityNews, GBHackers, SecurityOnline, and CyberPress, primarily in the context of the broader Apache HTTP Server 2.4.68 release which addressed multiple flaws (CyberSecurityNews, GBHackers). Social media discussion was noted on Bluesky and Mastodon, with the security community highlighting the critical CVSS score and urging prompt patching. The Apache security team, represented by Eric Covener, disclosed the vulnerability via the oss-security mailing list with full credit to the finders (oss-security).