Fortinet VPN Logging Flaw Enables Undetected Brute-Force Attacks

2024-11-22

Need some ammo against Fortinet? This article highlights a significant security flaw in Fortinet VPN that leaves organizations vulnerable to undetected brute-force attacks.

A design flaw in Fortinet VPN's logging system allows successful brute-force attacks to go unnoticed by logging only failed login attempts. Attackers can verify credentials after the authentication stage without proceeding to authorization, preventing successful attempts from being recorded. This vulnerability enables attackers to validate credentials without alerting defenders, posing a significant security risk as they could use or sell the verified credentials later. The flaw complicates the detection of successful breaches during incident response, although failed attempts still indicate an ongoing brute-force attack.

Key Facts

Risks:

Weak or Compromised Credentials, Other: Logging Flaw

Keywords:

Fortinet, VPN, brute-force attack, logging flaw, credential verification

CVE:

N/A

Affected:

Fortinet VPN

Article Body

Fortinet VPN Vulnerability Exposes Security Weakness

Overview of the Issue

A design flaw has been discovered in the Fortinet VPN server that can obscure successful brute-force attacks, posing a significant security risk. This flaw lies in the server's logging mechanism, which fails to record successful credential verification, misleading defenders into thinking that all login attempts have failed.

How the Flaw Works

The Fortinet VPN server logs login activity through a two-step process involving authentication and authorization. Typically, a successful login is recorded only after both steps are completed. However, researchers have found a way to stop the process after the authentication stage, allowing attackers to confirm valid credentials without logging the success.

Technical Breakdown

• Authentication and Authorization: The VPN server first checks if the credentials are valid (authentication) and then establishes a VPN session (authorization).
• Logging Mechanism: Failed login attempts are logged during the authentication phase, while successful logins are recorded only after authorization.
• Exploitation Technique: By halting the process after authentication, attackers can verify credentials without triggering a log entry for success.

Implications of the Vulnerability

This vulnerability enables attackers to conduct brute-force attacks without the risk of detection for successful attempts. Defenders may notice failed attempts, indicating an ongoing attack, but they won't be aware of any successful breaches. This gap in logging allows attackers to either use the verified credentials later or sell them to other malicious actors.

Potential Impact

The flaw complicates incident response efforts, as it hides successful logins amidst failed attempts, leaving security teams unaware of compromised credentials. While the authorization process includes additional checks, a resourceful attacker could bypass these defenses, potentially breaching an organization's network.

Read More

https://www.bleepingcomputer.com/news/security/fortinet-vpn-design-flaw-hides-successful-brute-force-attacks/