Summary

Vulnerability: Improper Session Invalidation on Account Deactivation (Broken Access Control / Logic Flaw)

• This vulnerability is caused by a backend logic flaw that maintains a false trust assumption that already-authenticated users remain trustworthy, even after their accounts are explicitly deactivated. As a result, administrative security actions do not behave as intended, allowing persistent unauthorized access.

Description

The application fails to immediately revoke active user sessions when an account is deactivated. Due to a logic flaw in the backend design, account state changes are enforced only during authentication (login), not for already-established sessions.

The system implicitly assumes that authenticated users remain trusted for the lifetime of their session. There is no session expiration or account expiration mechanism in place, causing deactivated accounts to retain indefinite access until the user manually logs out. This behavior breaks the intended access control policy and results in persistent unauthorized access, representing a critical security flaw.

Affected Functionality

• User session management and authentication logic
• Account deactivation mechanism
• All authenticated endpoints, including administrative and content interfaces

Attack Scenario

• A user logs into the application.
• An administrator deactivates the user account.
• The user remains fully logged in and can continue performing all actions allowed by their role indefinitely, as there is no session expiration.
• The user can continue invoking backend methods, triggering application actions, accessing sensitive interfaces (including user management if permitted), and interacting with the system as if the account were still active.
• Access is only lost if the user manually logs out, which may never occur.

Impact

• Unauthorized Continued Access: Deactivated users retain full access indefinitely, violating intended access control and expected security behavior.
• Bypass of Administrative Controls: Administrative actions (deactivation) fail to immediately restrict active sessions.
• Logic Flaw Resulting in Broken Behavior: Backend authorization logic relies on a flawed trust assumption that authenticated users remain valid, enforcing account state only at login.
• Full Functional Access Retained: Deactivated users can continue invoking application methods, executing actions, interacting with protected endpoints, and using the system exactly as before being deactivated.
• Privilege Abuse: Users with elevated roles (moderator, editor, administrator) can continue performing privileged actions after account deactivation, including accessing user management interfaces and modifying application state.