CVE-2026-48834: Apache Answer DoS Vulnerability

CVE-2026-48834 Overview

CVE-2026-48834 is a denial-of-service vulnerability in Apache Answer affecting all versions through 2.0.1. The flaw stems from improper handling of length parameter inconsistency [CWE-400] when parsing the HTTP Accept-Language header. Unauthenticated attackers can send a specially crafted Accept-Language header that triggers excessive CPU consumption during parsing. Apache has released version 2.0.2 to address the issue.

Critical Impact
Remote unauthenticated attackers can exhaust server CPU resources with a single crafted HTTP header, disrupting availability of Apache Answer deployments.

Affected Products

Apache Answer versions through 2.0.1
Apache Answer 2.0.2 (fixed version)
Q&A community platforms deploying Apache Answer

Discovery Timeline

2026-08-05 - CVE CVE-2026-48834 published to NVD
2026-08-05 - Last updated in NVD database

Technical Details for CVE-2026-48834

Vulnerability Analysis

Apache Answer processes the Accept-Language HTTP header on incoming requests to determine the user's preferred locale. The parser fails to validate length parameter consistency during header processing. An attacker can craft a header value that forces the parser into computationally expensive operations. Each malicious request consumes significant CPU time, and repeated requests degrade or halt service for legitimate users.

Because the vulnerable code path executes before authentication, any client that can reach the application can trigger the condition. The issue falls under [CWE-400] (Uncontrolled Resource Consumption), a class of algorithmic complexity flaws that convert small inputs into large computational costs.

Root Cause

The parser accepts length parameters in the Accept-Language header without reconciling them against the actual data present. This inconsistency drives inefficient parsing behavior. Apache's fix in version 2.0.2 adjusts input handling so length parameters are validated and parsing costs remain bounded.

Attack Vector

Exploitation requires only network access to the Apache Answer instance. The attacker sends HTTP requests containing a crafted Accept-Language header. No authentication, user interaction, or prior foothold is required. Concurrent requests amplify the impact, allowing a single low-bandwidth attacker to saturate CPU resources on the target host.

See the Apache Mailing List Thread and the Openwall OSS Security Update for the vendor announcement.

Detection Methods for CVE-2026-48834

Indicators of Compromise

Sustained high CPU utilization on Apache Answer application processes with no corresponding user activity spike.
HTTP request logs containing unusually long, malformed, or repetitive Accept-Language header values.
Elevated request latency and increased HTTP 5xx responses from Apache Answer endpoints.

Detection Strategies

Inspect web server and reverse proxy logs for Accept-Language headers exceeding normal length or containing repeated locale tokens.
Correlate spikes in CPU usage on Apache Answer hosts with request volume from single source IP addresses.
Deploy WAF rules that flag anomalously large or malformed Accept-Language headers before they reach the application.

Monitoring Recommendations

Alert on Apache Answer process CPU utilization exceeding baseline thresholds for sustained periods.
Track request-rate anomalies per source IP against Apache Answer endpoints.
Log full HTTP header values at the reverse proxy for forensic review of DoS attempts.

How to Mitigate CVE-2026-48834

Immediate Actions Required

Upgrade Apache Answer to version 2.0.2 or later, which contains the vendor fix.
Place Apache Answer behind a reverse proxy or WAF that enforces maximum header size and rejects malformed Accept-Language values.
Apply per-IP rate limiting on unauthenticated endpoints to reduce impact of DoS attempts.

Patch Information

Apache has released Apache Answer 2.0.2, which addresses the improper handling of length parameter inconsistency in Accept-Language parsing. All users running versions through 2.0.1 should upgrade immediately. Refer to the Apache Mailing List Thread for the official advisory.

Workarounds

Configure the upstream reverse proxy (for example, Nginx or Apache HTTPD) to cap Accept-Language header length and drop oversized values.
Restrict access to Apache Answer to trusted networks until the patch is applied.
Enable CPU and request-rate quotas at the container or process level to contain resource exhaustion.

bash

# Nginx example: limit Accept-Language header length and apply rate limiting
http {
    limit_req_zone $binary_remote_addr zone=answer_rl:10m rate=10r/s;

    server {
        listen 443 ssl;
        server_name answer.example.com;

        # Reject oversized Accept-Language headers before proxying
        if ($http_accept_language ~* ".{512,}") {
            return 400;
        }

        location / {
            limit_req zone=answer_rl burst=20 nodelay;
            proxy_pass http://apache_answer_backend;
        }
    }
}