2FA Bypass Using a Brute Force Attack

Overview

The Nagios Fusion application (version 2024R1.2 and 2024R2) is vulnerable to a Brute-Force attack on its Two-Factor Authentication (2FA) mechanism. Specifically, the 2FA implementation does not adequately enforce rate-limiting or account lockout mechanisms, allowing an attacker to bypass 2FA by repeatedly guessing the One-Time Password (OTP).

The following issues were observed:

• Lack of Rate-Limiting: The 2FA endpoint does not limit the number of OTP submission attempts.
• Weak Lockout Policy: No account lockout is triggered after repeated failed OTP attempts, enabling brute-force attacks to succeed.
• Potential for Unauthorized Access: With sufficient computational resources, an attacker could bypass 2FA and gain unauthorized access to sensitive accounts, including administrator accounts.

This vulnerability stems from the absence of proper defences against brute-force attacks, rendering the 2FA mechanism ineffective against targeted attacks.

Severity

• Severity: High
• CWE: CWE-307 (primary); CWE-287 (secondary)
• CVSS Score (v3.0): 7.6 High
• CVSS Vector: AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:L

Affected Components

• 2FA Verification Endpoint (e.g., /verify-otp)
• Authentication Middleware
• Session Issuance Service
• Rate Limiting / Anti-Automation Controls

Affected Vendor/Product

• Product Name- Nagios Fusion
• Affected Version: 2024R1.2 and 2024R2
• Fixed Version: 2024R2.1

Summary of the Issue

What Happens:

1. User attempts login with valid username and password.
2. System prompts for OTP from authenticator app/SMS/email.
3. Attacker scripts automated requests to /verify-otp endpoint.
4. Due to lack of rate limiting and lockout, attacker can attempt unlimited guesses.
5. Within feasible time, attacker predicts correct OTP and bypasses 2FA.

Security Posture Gap: 2FA is meant to increase entropy and reduce brute-force feasibility. Without proper anti-automation controls, OTP becomes brute-forceable, negating the second factor.

Abuse Scenarios:

• Automated credential stuffing + brute-force OTP to achieve mass account takeover.
• Targeted attack against high-value accounts where password was phished or leaked.

Mitigation Recommendations

• Enforce strict rate limiting per account/IP/device for OTP attempts.
• Lock account after N failed OTP attempts and require re-authentication.
• Introduce back-off delays (e.g., exponential) on repeated failures.

Disclosure Timeline

• [05-01-2025]: Vulnerability discovered

• [05-01-2025]: Reported to vendor

• [10-01-2025]: Vendor verified the vulnerability

• [23-07-2025]: Vendor patched the vulnerability with a new release

• [16-08-2025]: Apply For CVE

• [23-10-2025]: Assign CVE

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