CVSS 8.1 CVE-2021-36369
CVSS 8.1 CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
The Dropbear client through 2020.81 proceeds with establishing an SSH session even if it has never sent a substantive authentication response. This makes it easier for an attacker-controlled SSH server to present a later spoofed authentication prompt (that the attacker can use to capture credential data, and use that data for purposes that are undesired by the client user).
The trivial authentication phishing attack is described in Trivial Authentication.
Added client option “-o DisableTrivialAuth”. This can be used to prevent the server immediately accepting successful authentication (before any auth request) which could cause UI confusion and security issues with agent forwarding - it isn’t clear which host is prompting to use a key. Thanks to Manfred Kaiser from Austrian MilCERT