CVE-2026-48913

What it actually does

CVE-2026-48913 is a use-after-free vulnerability in Apache HTTP Server's mod_http2 module affecting versions 2.4.55 through 2.4.67. When the server has exhausted available file handles, mod_http2 can incorrectly continue operating on memory associated with an object that has already been freed. Because the flaw is reachable over the network without authentication and without user interaction, an attacker able to make HTTP/2 requests to an affected server may be able to trigger memory corruption. The stated CVSS impact is low confidentiality, integrity, and availability impact, meaning exploitation could potentially disclose limited process memory, corrupt request-handling state, or crash/unstabilize Apache worker processes, but the available public information does not indicate reliable remote code execution.

Why it matters to the business

Organizations running affected Apache HTTP Server versions with HTTP/2 enabled may face service instability or limited data exposure if an attacker can trigger the vulnerable error path during file-handle exhaustion. The most likely operational consequence is degradation or interruption of web services, especially under high connection or file descriptor pressure. Although this issue is not currently listed in CISA KEV, has no reported ransomware use, and has a low EPSS score, it is remotely reachable and affects a widely deployed internet-facing web server, so exposed systems should still be prioritized for normal patch cycles and hardening.

How an attack unfolds

An attacker first identifies an Apache HTTP Server instance that supports HTTP/2 and is running an affected version between 2.4.55 and 2.4.67. The attacker then creates conditions that exhaust or contribute to exhaustion of the server's available file handles, such as many concurrent connections, requests, streams, or interactions that cause Apache to open files or sockets. Once the file-handle exhaustion condition is reached, the attacker sends crafted HTTP/2 traffic intended to drive mod_http2 through the vulnerable cleanup/error-handling path. In that state, mod_http2 may reference memory that has already been freed, causing memory corruption. Depending on runtime behavior, allocator state, and server configuration, exploitation may result in worker crashes, abnormal HTTP/2 errors, limited memory disclosure, or corrupted request-handling behavior. No public exploit maturity or named threat actor activity was provided, so defenders should treat exploitation as plausible but not currently observed at scale based on the supplied intelligence.

How to fix it

Upgrade Apache HTTP Server to a vendor-released version that fixes this issue when available for the deployed distribution or appliance. The affected upstream range is Apache HTTP Server 2.4.55 through 2.4.67; apply the first fixed version or later from Apache or the operating system package maintainer. If an immediate upgrade is not possible, reduce exposure by disabling HTTP/2 support where it is not required, typically by removing or disabling mod_http2 and removing 'h2'/'h2c' from Protocols directives. Also harden resource limits to make file-handle exhaustion harder to reach: review operating system file descriptor limits, Apache worker limits, connection/request timeouts, MaxRequestWorkers, per-IP rate limits, reverse-proxy limits, and web application firewall or load balancer connection controls. Restart Apache after configuration changes or package upgrades, and confirm the active binary/module version rather than relying only on package metadata.

How to confirm the fix worked

Confirm whether Apache HTTP Server is in the affected range 2.4.55 through 2.4.67 and whether mod_http2 is loaded. Validate the remediated state by checking the active Apache version, loaded modules, and HTTP/2 protocol negotiation. Use commands such as 'httpd -v' or 'apache2 -v' to confirm version, 'httpd -M' or 'apache2ctl -M' to verify whether 'http2_module' is loaded, and configuration review to ensure 'Protocols' does not include 'h2' or 'h2c' if HTTP/2 was disabled as a mitigation. From a client, use 'curl --http2 -I https://example.com' or TLS ALPN checks to verify whether HTTP/2 is still negotiated. Review vendor package changelogs or security advisories to confirm the installed package includes the fix for CVE-2026-48913. After remediation, monitor error logs under controlled load for absence of file descriptor exhaustion messages, segmentation faults, child process crashes, and HTTP/2 stream errors.

Typical attack path

1. Reconnaissance: scan for internet-facing Apache HTTP Server instances that advertise HTTP/2 support.
2. Version assessment: infer or confirm the server is running Apache HTTP Server 2.4.55 through 2.4.67.
3. Resource pressure: open many concurrent connections, HTTP/2 sessions, streams, or requests to push the server toward file descriptor exhaustion.
4. Trigger condition: send HTTP/2 traffic while file handles are exhausted to exercise the vulnerable mod_http2 error-handling path.
5. Impact realization: cause Apache worker instability, crashes, request failures, or possible limited memory exposure/corruption.
6. Post-exploitation or follow-on activity: repeat triggering to create denial-of-service conditions or use instability as cover for other web-facing attacks.

How to detect it

To assess possible prior exploitation, review Apache access logs, error logs, system journals, crash reports, and reverse-proxy/load-balancer logs for patterns where high volumes of HTTP/2 requests or connections coincide with file descriptor exhaustion and Apache worker crashes. Key log sources include Apache error_log, access_log with protocol fields if enabled, systemd journal entries for httpd/apache2, kernel logs for segmentation faults, core dump metadata, load balancer HTTP/2 telemetry, and WAF/rate-limit logs. Look for bursts of HTTP/2 traffic from one or a small set of source IPs, many concurrent streams or short-lived requests, HTTP/2 protocol errors, 'Too many open files' messages, child process segmentation faults, unexpected graceful restarts, and 5xx spikes. If core dumps are available, preserve them and inspect whether crashes occurred in or near mod_http2 code paths. Because no specific public exploit payload or actor-specific artifacts are provided, detection should focus on behavioral correlation: HTTP/2-heavy resource exhaustion followed by mod_http2/Apache instability.

• Too many open files
• AH00015: Unable to open logs
• AH00016: Configuration Failed
• AH00484: server reached MaxRequestWorkers setting
• AH01114: HTTP: failed to make connection to backend
• AH02951: child pid
• segmentation fault
• core dumped
• http2_module
• mod_http2
• AH030
• AH034
• AH100
• AH101
• AH102
• AH103
• AH104
• AH105
• AH106
• AH02951: h2
• AH10034
• AH10035
• AH10036
• AH10037
• AH10038
• AH10039
• AH10040
• AH10041
• AH10042
• AH10043
• AH10044
• AH10045
• AH10046
• AH10047
• AH10048
• AH10049
• AH10050
• AH10051
• AH10052
• AH10053
• AH10054
• AH10055
• AH10056
• AH10057
• AH10058
• AH10059
• AH10060
• AH10061
• AH10062
• AH10063
• AH10064
• AH10065
• AH10066
• AH10067
• AH10068
• AH10069
• AH10070
• AH10071
• AH10072
• AH10073
• AH10074
• AH10075
• AH10076
• AH10077
• AH10078
• AH10079
• AH10080
• AH10081
• AH10082
• AH10083
• AH10084
• AH10085
• AH10086
• AH10087
• AH10088
• AH10089
• AH10090
• AH10091
• AH10092
• AH10093
• AH10094
• AH10095
• AH10096
• AH10097
• AH10098
• AH10099

What your security team should do

• Inventory Apache HTTP Server deployments and identify systems running versions 2.4.55 through 2.4.67 with mod_http2 enabled.
• Prioritize internet-facing, high-traffic, or business-critical web servers for upgrade or mitigation first.
• Apply vendor fixes as soon as available; where fixes are not yet deployed, disable HTTP/2 if it is not required.
• Review and tune file descriptor limits, Apache concurrency settings, request timeouts, and per-source connection limits to reduce the likelihood of file-handle exhaustion.
• Add monitoring for Apache error-log messages indicating 'Too many open files', HTTP/2 module failures, child process crashes, segmentation faults, or abnormal restart frequency.
• Check historical logs around traffic spikes for signs of HTTP/2-heavy connection bursts followed by Apache worker instability.
• Ensure load balancers, reverse proxies, and WAFs enforce sane HTTP/2 stream, connection, and request-rate limits.
• Track Apache and operating system vendor advisories for the exact fixed package version and backported patches.