CVE-2026-44631

What it actually does

CVE-2026-44631 is a memory corruption vulnerability in Apache HTTP Server 2.4.0 through 2.4.67 caused by a buffer underwrite when processing crafted regular expressions in server configuration. If vulnerable regular-expression handling is reachable during request processing, memory before an allocated buffer can be corrupted, potentially causing worker process crashes, denial of service, or, in the worst case, arbitrary code execution in the context of the Apache HTTP Server process. The CVSS vector indicates unauthenticated network reachability with low attack complexity and high confidentiality, integrity, and availability impact, although practical exploitability depends on how crafted regular expressions are introduced into or exercised by configuration.

Why it matters to the business

Successful exploitation could disrupt public web services, expose sensitive data handled by the web server, or allow attackers to tamper with served content and backend traffic routing. Because Apache HTTP Server is widely deployed as an internet-facing component, vulnerable versions can create broad operational risk even though the issue is not currently listed in CISA KEV, is not marked as ransomware-used, has low EPSS, and has no reported public exploit maturity. Organizations should still treat this as high priority due to the critical CVSS score and the role web servers play at the edge of production environments.

How an attack unfolds

An attacker first identifies an Apache HTTP Server instance running a vulnerable 2.4.x release. Exploitation requires the vulnerable regular-expression path to be present in configuration and reachable, such as configuration directives that evaluate regular expressions against request attributes. The attacker then sends crafted HTTP requests designed to exercise the vulnerable expression handling. When Apache processes the expression, the buffer underwrite corrupts adjacent memory. Depending on allocator behavior, process isolation, build options, and the exact configuration, the result may range from child process termination and repeated service instability to controlled memory corruption that could enable code execution as the web server user. If an attacker can also influence configuration content through a compromised deployment pipeline, control panel, or local administrative access, they may attempt to place a crafted expression directly into configuration and then trigger it remotely.

How to fix it

Upgrade Apache HTTP Server to version 2.4.68 or later. All Apache HTTP Server versions from 2.4.0 through 2.4.67 should be considered affected. Prefer vendor-supported packages from the operating system or appliance vendor when Apache is supplied as part of a distribution. After upgrading, fully restart Apache rather than relying only on graceful reloads where old worker processes may remain. As interim mitigation where immediate upgrade is not possible, restrict access to administrative interfaces and configuration deployment paths, review and simplify complex regular expressions in Apache configuration, disable unused modules that evaluate regular expressions, apply WAF/rate-limiting controls for crash attempts, and ensure the Apache process runs with least privilege and strong system confinement such as SELinux, AppArmor, systemd sandboxing, or chroot where applicable.

How to confirm the fix worked

Confirm the installed runtime version reports Apache HTTP Server 2.4.68 or later using commands such as `httpd -v`, `apache2 -v`, package manager inventory, or container image metadata. Verify that all running Apache master and worker processes were restarted after the upgrade and are not still using an older binary. Check that load-balanced pools, standby nodes, container base images, golden images, and appliance-managed instances were also updated. Review Apache configuration for complex or externally managed regular expressions and confirm only trusted administrators or deployment systems can modify them. Run a controlled configuration test with `apachectl configtest` or equivalent after patching, then monitor error logs and service health for segmentation faults or abnormal worker exits.

Typical attack path

1. Identify internet-facing Apache HTTP Server instances and determine whether they are running versions 2.4.0 through 2.4.67.
2. Fingerprint modules and behavior that suggest request-time regular-expression evaluation is in use, such as rewrite, access-control, header, environment, proxy, or matching rules.
3. Send crafted HTTP requests intended to trigger configured regular expressions and observe crashes, abnormal responses, or timing differences.
4. Refine payloads to achieve reliable process crashes or memory corruption under the target configuration.
5. If exploitation is successful, abuse the Apache worker process context to disrupt service, access data available to the web server process, modify web content, pivot to backend services, or establish persistence through web-accessible files or configuration changes.

How to detect it

There are no widely reliable, CVE-specific public indicators of exploitation provided for this issue. To determine whether exploitation may have occurred, review Apache access logs, error logs, system journals, crash reports, core dumps, EDR telemetry, and configuration audit logs from the period before patching. Focus on unexplained Apache worker crashes, repeated segmentation faults, abnormal restart loops, suspicious bursts of unusual HTTP requests immediately preceding crashes, and recent unauthorized changes to Apache configuration files containing regular expressions. Correlate HTTP requests before crashes with source IPs, user agents, request paths, headers, and request rates. Investigate any newly created or modified web content, unexpected Apache modules, changed virtual host files, altered rewrite rules, unexpected outbound connections from the Apache process, or child processes spawned by the web server user. Because exploitation may be configuration-dependent, absence of a single signature does not prove absence of exploitation.

• Apache/2.4.0
• Apache/2.4.1
• Apache/2.4.2
• Apache/2.4.3
• Apache/2.4.4
• Apache/2.4.5
• Apache/2.4.6
• Apache/2.4.7
• Apache/2.4.8
• Apache/2.4.9
• Apache/2.4.10
• Apache/2.4.11
• Apache/2.4.12
• Apache/2.4.13
• Apache/2.4.14
• Apache/2.4.15
• Apache/2.4.16
• Apache/2.4.17
• Apache/2.4.18
• Apache/2.4.19
• Apache/2.4.20
• Apache/2.4.21
• Apache/2.4.22
• Apache/2.4.23
• Apache/2.4.24
• Apache/2.4.25
• Apache/2.4.26
• Apache/2.4.27
• Apache/2.4.28
• Apache/2.4.29
• Apache/2.4.30
• Apache/2.4.31
• Apache/2.4.32
• Apache/2.4.33
• Apache/2.4.34
• Apache/2.4.35
• Apache/2.4.36
• Apache/2.4.37
• Apache/2.4.38
• Apache/2.4.39
• Apache/2.4.40
• Apache/2.4.41
• Apache/2.4.42
• Apache/2.4.43
• Apache/2.4.44
• Apache/2.4.45
• Apache/2.4.46
• Apache/2.4.47
• Apache/2.4.48
• Apache/2.4.49
• Apache/2.4.50
• Apache/2.4.51
• Apache/2.4.52
• Apache/2.4.53
• Apache/2.4.54
• Apache/2.4.55
• Apache/2.4.56
• Apache/2.4.57
• Apache/2.4.58
• Apache/2.4.59
• Apache/2.4.60
• Apache/2.4.61
• Apache/2.4.62
• Apache/2.4.63
• Apache/2.4.64
• Apache/2.4.65
• Apache/2.4.66
• Apache/2.4.67
• exit signal Segmentation fault
• segfault at
• core dumped
• AH00051: child pid
• AH00052: child pid

What your security team should do

• Prioritize patching internet-facing Apache HTTP Server deployments to 2.4.68 or later despite the currently low EPSS and absence from CISA KEV, because the CVSS impact is critical.
• Inventory Apache HTTP Server versions across servers, containers, appliances, reverse proxies, and embedded application stacks.
• Restart services after patching and verify no vulnerable Apache worker processes remain resident.
• Review configuration-management permissions and audit recent changes to Apache configuration files, especially directives containing regular expressions.
• Monitor Apache error logs, system logs, core dumps, EDR telemetry, and WAF logs for crashes or probing against regex-driven request handling.
• Temporarily increase monitoring and rate limiting on exposed Apache services until patch coverage is confirmed.
• Disable unused Apache modules and remove unnecessary complex regular expressions from configuration to reduce reachable attack surface.
• If unexplained Apache crashes are found, preserve logs, core dumps, binaries, configuration, and process telemetry before remediation for forensic review.