tinyauthapp Tinyauth up to 5.0.x Login Endpoint user_controller.go loginHandler improper authorization

Summaryinfo

A vulnerability identified as problematic has been detected in tinyauthapp Tinyauth up to 5.0.x. This affects the function loginHandler of the file internal/controller/user_controller.go of the component Login Endpoint. The manipulation leads to improper authorization. This vulnerability is traded as CVE-2026-77561. It is possible to initiate the attack remotely. There is no exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in tinyauthapp Tinyauth up to 5.0.x. This issue affects the function loginHandler of the file internal/controller/user_controller.go of the component Login Endpoint. The manipulation with an unknown input leads to a improper authorization vulnerability. Using CWE to declare the problem leads to CWE-285. The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action. Impacted is availability. The summary by CVE is:

Tinyauth is an authentication and authorization server. Prior to 5.1.0, an unauthenticated remote attacker can send POST /api/user/login requests with 257 distinct nonexistent usernames to fill MaxLoginAttemptRecords and activate a global login lockdown. internal/controller/user_controller.go loginHandler passes each attacker-controlled identifier to internal/service/auth_service.go RecordLoginAttempt, which invokes lockdownMode after the map reaches its cap. IsAccountLocked checks that global state before validating unrelated accounts, causing valid users to receive HTTP 429 until auth.loginTimeout expires, approximately 300 seconds by default. The attack can be repeated, but existing authenticated sessions are not invalidated. This issue is fixed in version 5.1.0.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-77561 since 08/20/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1548.002 according to MITRE ATT&CK.

Upgrading to version 5.1.0 eliminates this vulnerability.

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Productinfo

Vendor

• tinyauthapp

Name

• Tinyauth

Version

• 5.0

Website

• Product: https://github.com/tinyauthapp/tinyauth/

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