CVE-2026-76646: Resource Exhaustion DOS Vulnerability

CVE-2026-76646 Overview

CVE-2026-76646 is a resource consumption vulnerability [CWE-400] affecting an Apache project. A remote attacker can supply specially crafted request parameters that trigger excessive resource use on the target. The resulting exhaustion can produce a denial of service (DoS) condition against affected services.

The issue affects multiple release branches. Fixed versions are 2.3.12, 2.3-next-M9, 3.0.4, 4.0.4, and 4.1.4. Older unsupported versions may also be affected. The advisory was published through Apache and Openwall channels on 2026-09-16.

Critical Impact
A remote, unauthenticated attacker can trigger service-wide denial of service by sending crafted request parameters, disrupting availability for all consumers of the affected endpoint.

Affected Products

Affected Apache product versions prior to 2.3.12
Affected Apache product versions prior to 3.0.4 and 4.0.4
Affected Apache product versions prior to 4.1.4 and 2.3-next-M9

Discovery Timeline

2026-09-16 - CVE-2026-76646 published to NVD
2026-09-16 - Coordinated disclosure via Apache mailing list and Openwall OSS-Security
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-76646

Vulnerability Analysis

The vulnerability is classified as Uncontrolled Resource Consumption [CWE-400]. The affected component fails to bound the work performed while parsing or processing request parameters supplied by remote clients. An attacker who crafts specific parameter values can force the server to consume disproportionate CPU, memory, or thread resources relative to the size of the request.

Sustained exploitation degrades response times and can render the service unavailable to legitimate clients. Because the flaw is triggered through normal request handling paths, exploitation does not require authentication or user interaction. Refer to the Apache Mailing List Discussion and the Openwall OSS Security Update for advisory details.

Root Cause

The root cause is missing or insufficient limits on the resources consumed while processing attacker-controlled request parameters. The affected code paths lack input size validation, iteration caps, or complexity bounds. Crafted inputs therefore drive worst-case processing behavior.

Attack Vector

Exploitation occurs over the network by issuing HTTP requests containing crafted parameter values to an exposed endpoint of a vulnerable Apache instance. Repeated or parallel requests amplify the impact and can exhaust available worker threads or heap memory. See the referenced Apache advisory for scope and endpoint specifics.

Detection Methods for CVE-2026-76646

Indicators of Compromise

Sudden and sustained increases in CPU or memory utilization on Apache service hosts that correlate with inbound HTTP traffic.
Growing request queue depth, thread pool saturation, or rising HTTP 5xx error rates without a corresponding rise in legitimate traffic volume.
Repeated requests from a small set of source addresses containing unusually large, deeply nested, or repetitive parameter values.

Detection Strategies

Inventory Apache deployments and compare installed versions against the fixed releases 2.3.12, 2.3-next-M9, 3.0.4, 4.0.4, and 4.1.4.
Deploy web application firewall (WAF) rules that flag oversized query strings, excessive parameter counts, and abnormal parameter structures.
Correlate application performance metrics with access logs to identify request patterns that precede resource spikes.

Monitoring Recommendations

Ingest Apache access and error logs into a centralized analytics platform and alert on anomalies in request duration and parameter size distributions.
Enable process-level telemetry on Apache hosts to detect abrupt memory growth, thread saturation, and out-of-memory events.
Track rate-limit and connection-limit counters to identify sources sending traffic patterns consistent with resource exhaustion.

How to Mitigate CVE-2026-76646

Immediate Actions Required

Upgrade affected Apache installations to 2.3.12, 2.3-next-M9, 3.0.4, 4.0.4, or 4.1.4 as applicable to your release branch.
Restrict network exposure of the affected endpoints to trusted clients while patching is in progress.
Enable rate limiting and request-size limits at the reverse proxy or WAF layer in front of Apache services.

Patch Information

The vendor advisory instructs users to upgrade to 2.3.12, 2.3-next-M9, 3.0.4, 4.0.4, or 4.1.4, which fix this issue. Older, unsupported branches may also be affected and should be migrated to a supported fixed release. See the Apache Mailing List Discussion for release notes and upgrade guidance.

Workarounds

Enforce maximum request body and query string sizes at an upstream proxy or load balancer.
Apply per-source connection and request rate limits to constrain the volume of crafted requests any single client can send.
Configure resource ceilings such as worker thread caps, request timeouts, and JVM heap limits to contain the blast radius of exhaustion attempts.

bash

# Configuration example: nginx front-proxy hardening against parameter abuse
http {
    client_max_body_size 1m;
    large_client_header_buffers 4 8k;
    limit_req_zone $binary_remote_addr zone=req_limit:10m rate=10r/s;

    server {
        listen 443 ssl;
        location / {
            limit_req zone=req_limit burst=20 nodelay;
            proxy_read_timeout 15s;
            proxy_pass http://apache_backend;
        }
    }
}