CVE-2024-26578: Apache Answer Race Condition Vulnerability

CVE-2024-26578 Overview

CVE-2024-26578 is a race condition vulnerability affecting Apache Answer versions through 1.2.1. The flaw resides in the user registration workflow, where concurrent execution using a shared resource lacks proper synchronization [CWE-362]. Attackers can script rapid, parallel registration submissions to create multiple user accounts that share the same username. This breaks the uniqueness constraint on user identities and undermines account integrity across the platform. The Apache Software Foundation addressed the issue in Apache Answer version 1.2.5.

Critical Impact
Unauthenticated attackers can bypass username uniqueness enforcement by submitting concurrent registration requests, producing duplicate accounts that compromise identity integrity in Apache Answer deployments.

Affected Products

Apache Answer versions through 1.2.1
All deployments exposing the registration endpoint to network clients
Self-hosted Q&A community instances built on Apache Answer

Discovery Timeline

2024-02-22 - CVE CVE-2024-26578 published to NVD
2024-02-22 - Apache Software Foundation published advisory on the Apache Mailing List Thread
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-26578

Vulnerability Analysis

The vulnerability stems from missing synchronization around the shared username uniqueness check during account registration. Apache Answer verifies that a requested username does not already exist before writing the new user record to the database. Between that check and the insert, no lock or atomic constraint blocks parallel requests from passing the same validation. Attackers exploit this Time-of-Check to Time-of-Use (TOCTOU) window by submitting many registration requests simultaneously with identical username payloads.

Each concurrent request observes an empty result during the existence check, then proceeds to create a distinct user row. The outcome is multiple accounts sharing the same display name, which corrupts user attribution, breaks moderation workflows, and enables impersonation. Because the attack requires only unauthenticated network access to a public registration endpoint, exploitation is straightforward once the timing window is understood.

Root Cause

The root cause is Concurrent Execution using Shared Resource with Improper Synchronization [CWE-362]. The registration handler in Apache Answer through 1.2.1 performs the uniqueness check and the subsequent user insert as separate, non-atomic operations without a mutex, unique database constraint enforcement path, or transactional isolation sufficient to serialize concurrent writers.

Attack Vector

Exploitation requires network access to the Apache Answer registration endpoint and no authentication or user interaction. An attacker uses a scripted client to fire multiple POST requests to the registration API in parallel, each carrying the same target username and valid registration fields. When the requests reach the server within the vulnerable window, the application creates several accounts with the same name.

No verified public exploit code is available. See the OpenWall OSS Security Update for the vendor's technical description of the flaw.

Detection Methods for CVE-2024-26578

Indicators of Compromise

Multiple user records sharing an identical username or display_name in the Apache Answer database
Bursts of POST requests to the /answer/api/v1/user/register/email endpoint from a single source within a narrow time window
Registration success events for the same username originating from concurrent HTTP connections

Detection Strategies

Query the users table for duplicate usernames or display names created within seconds of each other
Alert on registration request rates exceeding a baseline threshold per source IP or per username value
Correlate web server access logs with application audit logs to identify registration bursts that produce more than one successful account creation

Monitoring Recommendations

Instrument the registration endpoint with rate-limit metrics and log the outcome of each request, including the created user ID
Forward Apache Answer application logs and reverse proxy access logs to a centralized SIEM or data lake for correlation
Schedule periodic integrity checks that flag any username collision or unexpected duplication in the identity store

How to Mitigate CVE-2024-26578

Immediate Actions Required

Upgrade Apache Answer to version 1.2.5 or later, which fixes the race condition in the registration flow
Audit the existing user database for duplicate usernames and remediate affected accounts before restoring normal operations
Place a rate limit on the registration endpoint at the reverse proxy or web application firewall layer to reduce exploitation windows

Patch Information

The Apache Software Foundation fixed CVE-2024-26578 in Apache Answer 1.2.5. Administrators should follow the upgrade guidance in the Apache Mailing List Thread and validate the deployed version after upgrading. No supported downgrade path preserves the fix.

Workarounds

Enforce a unique index on the username column at the database layer to reject duplicate inserts even if the application check races
Restrict access to the registration endpoint with CAPTCHA, email verification, or invitation flows to slow scripted concurrent submissions
Deploy a WAF rule that throttles repeated registration attempts from the same source or targeting the same username field value

bash

# Configuration example: rate-limit the Apache Answer registration endpoint with Nginx
limit_req_zone $binary_remote_addr zone=answer_register:10m rate=5r/m;

server {
    location /answer/api/v1/user/register/email {
        limit_req zone=answer_register burst=2 nodelay;
        proxy_pass http://answer_backend;
    }
}