CVE-2026-41418: 4ga Boards Auth Bypass Vulnerability

CVE-2026-41418 Overview

CVE-2026-41418 is a timing side-channel vulnerability in 4ga Boards, a realtime project management boards system. Prior to version 3.3.5, the application is vulnerable to user enumeration via timing analysis of the login endpoint (POST /api/access-tokens). An attacker can determine whether a username or email exists in the system by measuring response times, as valid accounts trigger a computationally expensive bcrypt.compareSync() operation while invalid accounts return immediately.

Critical Impact
Attackers can enumerate valid user accounts through timing analysis, facilitating targeted credential stuffing, phishing campaigns, and brute-force attacks against known-valid usernames.

Affected Products

4ga Boards versions prior to 3.3.5

Discovery Timeline

2026-04-24 - CVE CVE-2026-41418 published to NVD
2026-04-27 - Last updated in NVD database

Technical Details for CVE-2026-41418

Vulnerability Analysis

This vulnerability represents a classic timing side-channel attack (CWE-208) that exploits the observable behavioral difference in how the authentication system handles valid versus invalid usernames. The root issue lies in the authentication flow's conditional execution of computationally expensive password verification operations.

When a user submits login credentials to the /api/access-tokens endpoint, the server follows different code paths depending on whether the submitted username exists in the database. For non-existent usernames, the server responds almost immediately with an average response time of approximately 17 milliseconds. However, when a valid username is provided (even with an incorrect password), the server must perform a bcrypt.compareSync() password hash comparison, which introduces significant computational overhead resulting in an average response time of approximately 74 milliseconds.

The approximately 4.4× timing difference between these two scenarios is substantial enough to be reliably detected over network connections. Unlike many timing side-channels that require statistical analysis of thousands of requests, this vulnerability is exploitable with a single request per username, making enumeration highly efficient and difficult to rate-limit effectively.

Root Cause

The vulnerability stems from the authentication endpoint's failure to normalize response times for all authentication attempts. The application only invokes the expensive bcrypt.compareSync() operation when a valid user account is found, creating a measurable timing discrepancy. Proper secure authentication implementations should perform equivalent computational work regardless of whether the username exists, typically by comparing the submitted password against a dummy hash when no account is found.

Attack Vector

The attack is conducted over the network against the login endpoint without requiring any authentication or special privileges. An attacker can systematically probe the /api/access-tokens endpoint with lists of potential usernames or email addresses, measuring the response time for each request. Responses returning in approximately 17ms indicate non-existent accounts, while responses taking approximately 74ms confirm valid accounts exist in the system.

This enumeration data can then be leveraged for:

Targeted credential stuffing attacks against confirmed valid accounts
Spear phishing campaigns with verified email addresses
Password brute-forcing focused only on known-valid usernames
Social engineering attacks with confirmed user identity information

Detection Methods for CVE-2026-41418

Indicators of Compromise

Unusual patterns of sequential authentication failures to the /api/access-tokens endpoint from single source IPs
High volume of login attempts with unique usernames/emails from the same source
Consistent rapid-fire requests to the login endpoint with varying response times
Authentication log entries showing systematic testing of email formats or username patterns

Detection Strategies

Monitor authentication endpoint request rates and flag anomalous patterns exceeding normal user behavior thresholds
Implement logging that captures response time distributions for failed authentication attempts
Deploy web application firewall (WAF) rules to detect sequential enumeration-style request patterns
Configure intrusion detection systems to alert on high-frequency login attempts from single sources

Monitoring Recommendations

Enable detailed timing metrics for the authentication endpoint in application performance monitoring tools
Set up alerts for authentication failure rates exceeding baseline thresholds per source IP
Review authentication logs regularly for patterns suggesting systematic username enumeration
Monitor for reconnaissance activity that may precede credential-based attacks

How to Mitigate CVE-2026-41418

Immediate Actions Required

Upgrade 4ga Boards to version 3.3.5 or later immediately
Review authentication logs for evidence of prior enumeration attempts
Consider implementing additional rate limiting on the login endpoint
Enable account lockout policies to limit brute-force attack effectiveness

Patch Information

The vulnerability is fixed in 4ga Boards version 3.3.5. Organizations should upgrade to this version or later to remediate the timing side-channel issue. For detailed information about the security fix, refer to the GitHub Security Advisory.

Workarounds

Implement aggressive rate limiting on the /api/access-tokens endpoint to slow enumeration attempts
Deploy a reverse proxy or WAF with timing normalization capabilities
Add artificial random delays to authentication responses (note: this is a temporary measure that may impact user experience)
Consider implementing CAPTCHA or proof-of-work challenges after initial failed attempts

bash

# Example nginx rate limiting configuration for the login endpoint
# Add to your nginx server configuration
limit_req_zone $binary_remote_addr zone=login_limit:10m rate=5r/m;

location /api/access-tokens {
    limit_req zone=login_limit burst=3 nodelay;
    proxy_pass http://backend;
}