CVE-2025-24806 in Authelia
Summary
by MITRE • 02/19/2025
Authelia is an open-source authentication and authorization server providing two-factor authentication and single sign-on (SSO) for applications via a web portal. If users are allowed to sign in via both username and email the regulation system treats these as separate login events. This leads to the regulation limitations being effectively doubled assuming an attacker using brute-force to find a user password. It's important to note that due to the effective operation of regulation where no user-facing sign of their regulation ban being visible either via timing or via API responses, it's effectively impossible to determine if a failure occurs due to a bad username password combination, or a effective ban blocking the attempt which heavily mitigates any form of brute-force. This occurs because the records and counting process for this system uses the method utilized for sign in rather than the effective username attribute. This has a minimal impact on account security, this impact is increased naturally in scenarios when there is no two-factor authentication required and weak passwords are used. This makes it a bit easier to brute-force a password. A patch for this issue has been applied to versions 4.38.19, and 4.39.0. Users are advised to upgrade. Users unable to upgrade should 1. Not heavily modify the default settings in a way that ends up with shorter or less frequent regulation bans. The default settings effectively mitigate any potential for this issue to be exploited. and 2. Disable the ability for users to login via an email address.
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Analysis
by VulDB Data Team • 02/19/2025
CVE-2025-24806 represents a significant authentication vulnerability within Authelia's access control mechanisms that stems from improper handling of user identification during login attempts. This flaw manifests when the system allows users to authenticate using either their username or email address, creating a fundamental inconsistency in how authentication attempts are tracked and regulated. The vulnerability operates through a critical design oversight where the system's rate limiting and regulation mechanisms count login attempts based on the authentication method used rather than the actual user identity, effectively doubling the regulation limits for accounts that can be accessed via multiple identifiers.
The technical implementation of this vulnerability aligns with CWE-305 authentication bypass patterns where the system fails to properly correlate authentication attempts to individual user accounts. When an attacker targets a user account that can be accessed via both username and email, they can effectively double their chances of bypassing rate limiting protections by alternating between the two authentication methods. This creates a scenario where the system's built-in security controls become less effective, as demonstrated by the specific impact where the regulation limitations appear to be doubled, making brute-force attacks more feasible than they should be under normal circumstances.
The operational impact of this vulnerability extends beyond simple rate limiting considerations, as it introduces a covert mechanism that prevents users from understanding why authentication attempts are failing. This characteristic creates a significant blind spot in the security posture, as attackers cannot distinguish between legitimate authentication failures due to incorrect credentials versus failures caused by the system's regulation mechanisms. The lack of user-facing indicators or API response differences means that the system operates in a way that hides the actual cause of authentication failures, which fundamentally undermines the security model's ability to provide meaningful protection against automated attack vectors.
The vulnerability's exploitation potential is particularly concerning in environments where two-factor authentication is not enforced, as it creates a direct pathway for password brute-forcing attacks. When combined with weak password policies, this vulnerability becomes significantly more dangerous as the reduced authentication complexity makes the doubled rate limiting effect more impactful. The default configuration of Authelia effectively mitigates this risk through its conservative regulation settings, but administrators who modify these defaults without understanding the implications create additional attack surface. This behavior aligns with ATT&CK technique T1110.003 for credential stuffing and password spraying attacks where attackers exploit system weaknesses in authentication controls.
Organizations implementing Authelia must understand that this vulnerability operates at the intersection of authentication design and access control enforcement. The patch released in versions 4.38.19 and 4.39.0 addresses the core issue by ensuring that authentication attempts are properly correlated to user identities regardless of the authentication method used. System administrators should prioritize upgrading to these patched versions as the most effective mitigation strategy. For environments where immediate upgrades are not possible, the recommended mitigations include maintaining default regulation settings and disabling email-based authentication options, which effectively eliminates the vulnerability's exploitation vectors. The vulnerability demonstrates how seemingly minor configuration decisions can significantly impact overall system security and highlights the importance of proper authentication correlation mechanisms in security-critical applications.