An authentication gap is a mismatch in login protection, where one access path requires strong controls such as multi-factor authentication while another still accepts passwords alone. In practice, this often happens when cloud applications are protected better than VPN, RDP, Windows sign-ins, or other legacy systems. The result is a patchwork identity environment, not a single security policy.
This matters because attackers do not need to break strong MFA if a weaker path still exists. Stolen or reused credentials can be tested against the least protected login route and may succeed as a normal, valid-account sign-in. That makes detection harder and gives attackers a foothold for internal access, privilege abuse, or lateral movement. Defenders reduce the risk by inventorying every authentication entry point, enforcing MFA everywhere possible, removing password-only exceptions, and monitoring for inconsistent login patterns across cloud, remote access, and on-prem systems.