CVE-2026-48913: Apache HTTP Server mod_http2 Use-After-Free (File Handle Exhaustion)

Technical summary

CVE-2026-48913 is a use-after-free vulnerability (CWE-416) in the mod_http2 module of Apache HTTP Server. The flaw emerges in a resource exhaustion scenario: when the operating system or application has exhausted available file descriptors, the module's HTTP/2 connection handling code fails to properly manage object lifecycle, resulting in freed memory being accessed in subsequent operations. This memory safety violation can corrupt heap state and enable arbitrary read or write primitives. The vulnerability has a CVSS v3.1 score of 7.3 (HIGH severity) with a network attack vector, low attack complexity, and no privilege or user interaction requirements.

Business impact

Organizations running affected Apache HTTP Server versions face potential service availability disruption if the vulnerability is triggered. The combination of information disclosure and integrity impact means an attacker could exfiltrate sensitive data (including session tokens or configuration details) or modify server responses in transit. In multi-tenant or upstream proxy scenarios, a single compromised connection could leak or corrupt data for multiple downstream clients. Remediation requires coordinated patching, which may necessitate brief maintenance windows during low-traffic periods.

Affected systems

Apache HTTP Server versions 2.4.55 through 2.4.67 are affected. Organizations should inventory deployments with mod_http2 enabled (HTTP/2 support is often enabled by default in modern configurations). Systems running older versions (pre-2.4.55) are not impacted. Verify your exact version via 'httpd -v' or in your vendor's system information. This vulnerability does not affect Apache HTTP Server 2.2.x or earlier branches.

Exploitability

The vulnerability requires no authentication and can be triggered remotely over the network. However, practical exploitation depends on inducing a file handle exhaustion condition on the target server—a prerequisite that requires either sustained connection flooding or awareness of the system's resource limits. Once file descriptors are exhausted and an HTTP/2 request arrives, the use-after-free is likely to be triggered on vulnerable versions. Exploit code has not been publicly disclosed as of the vulnerability publication date, and the issue is not currently tracked on CISA's Known Exploited Vulnerabilities (KEV) catalog.

Remediation

Upgrade Apache HTTP Server to a patched version released after June 17, 2026 (the last modification date in the advisory). Consult the official Apache HTTP Server security advisory for the specific patched version number and upgrade path. If immediate patching is not feasible, consider disabling mod_http2 or restricting HTTP/2 connections to trusted clients via firewall rules. Monitor file descriptor usage on production systems to identify resource pressure that could trigger the vulnerability.

Patch guidance

Check the Apache HTTP Server official security advisory (apache.org) for the specific patched version available for your release branch. Most deployments will upgrade to the first available version after 2.4.67 that contains the fix. If you manage source builds, apply the relevant patch from the Apache repository. For packaged distributions (Red Hat, Debian, etc.), monitor vendor security bulletins—patches often arrive within 1–2 weeks of the upstream fix. Test patched versions in a staging environment before production rollout to ensure compatibility with your module configuration and workloads.

Detection guidance

Monitor system logs for repeated file descriptor exhaustion warnings (check ulimit and /proc/sys/fs/file-max on Linux). Enable Apache access and error logging at DEBUG level on a test system to observe HTTP/2 frame processing during file handle saturation. Look for segmentation faults or abort signals in httpd error logs that coincide with high connection counts. Use tools like 'lsof' to track open file descriptors per httpd process in real time. Network-based detection is challenging without deep packet inspection of HTTP/2 frames, so prioritize log-based and system-level indicators.

Why prioritize this

This vulnerability merits prompt but not emergency patching. The 7.3 CVSS score reflects genuine impact (information disclosure, integrity, and availability), but exploitation requires an uncommon prerequisite (file descriptor exhaustion). Organizations with robust connection rate limiting and resource monitoring in place face lower immediate risk. Prioritize patching internet-facing web servers, reverse proxies, and edge deployments before internal services. The lack of active exploitation in the wild (KEV status: false) allows a brief window for coordinated rollout planning.

Risk score, explained

The CVSS 7.3 (HIGH) score reflects three key factors: (1) network-accessible attack vector with low complexity, (2) no authentication or user interaction required, (3) multiple impact categories (confidentiality, integrity, availability). The score is not critical (8.0+) because exploitation requires triggering a specific resource exhaustion state, which is not trivial in well-tuned production environments. Organizations with file descriptor limits properly tuned to their workload and connection rate limiting in place will have substantially lower practical risk.

Frequently asked questions