The Vulnerability in Authelia

 The Vulnerability in Authelia

Authelia is an open-source authentication and authorization server designed to provide secure access to applications through features like two-factor authentication and single sign-on (SSO) via a web portal. It plays a crucial role in identity and access management (IAM) for web applications. 

CVE-2025-24806 is a vulnerability affecting Authelia's regulation system when users are allowed to sign in using both usernames and email addresses. The regulation system treats these login methods as separate events, effectively doubling the number of attempts an attacker can make using brute-force methods to guess passwords. This vulnerability does not provide visible indicators of regulation bans, making it difficult to distinguish between login failures due to incorrect credentials or an active ban. 

The impact of this vulnerability is minimal on account security, but it increases in scenarios where two-factor authentication is not required and weak passwords are used. In such cases, it becomes slightly easier for attackers to brute-force passwords. However, the lack of user-facing indicators for regulation bans mitigates the risk by making it harder for attackers to determine if their attempts are being blocked by a ban or incorrect credentials.

To address CVE-2025-24806, users are advised to update Authelia to versions 4.38.19 or 4.39.0. For those unable to upgrade, two temporary measures can be taken:

1. : Do not alter the default settings in a way that results in shorter or less frequent regulation bans. The default settings effectively mitigate the potential for exploitation.

2. : Disable the ability for users to log in via email addresses. This prevents the regulation system from treating username and email logins as separate events. 

Consider a scenario where an organization uses Authelia to manage access to its internal web applications. The organization allows users to log in using both their usernames and email addresses. An attacker attempts to brute-force a user's password by trying multiple combinations. Because Authelia treats these login methods separately, the attacker can effectively double the number of attempts before triggering a regulation ban. However, if the organization disables email login or upgrades to a patched version of Authelia, the vulnerability is mitigated, reducing the risk of successful brute-force attacks.

Conclusion

CVE-2025-24806 highlights the importance of maintaining up-to-date security patches and configuring authentication systems carefully to prevent exploitation. By understanding and addressing this vulnerability, organizations can enhance the security of their authentication processes and protect against brute-force attacks

• https://nvd.nist.gov/