Nagios Fusion versions prior to R2.1 contain a vulnerability due to the application not requiring re-authentication or session rotation when a user has enabled two-factor authentication (2FA). As a result, an adversary who has obtained a valid session could continue using the active session after the target user enabled 2FA, potentially preventing the legitimate user from locking the attacker out and enabling persistent account takeover.
According to WASC, “Insufficient Session Expiration is when a web site permits an attacker to reuse old session credentials or session IDs for authorization.”