CVE-2021-36369: 
Linux Debian vulnerability analysis and mitigation

A vulnerability (CVE-2021-36369) was discovered in Dropbear through version 2020.81, affecting the client-side SSH code. The issue stems from a non-RFC-compliant check of the available authentication methods, which could allow an SSH server to manipulate the login process (CVE Details, NVD).

The vulnerability arises from a non-RFC-compliant implementation in the client-side SSH authentication method verification. This flaw could enable a malicious SSH server to alter the authentication process in its favor, potentially bypassing additional security measures such as FIDO2 tokens or SSH-Askpass. The issue was particularly concerning when using agent forwarding, as it could allow unnoticed authentication to other servers (Debian LTS).

The vulnerability's primary impact is the potential bypass of additional security measures, including FIDO2 tokens and SSH-Askpass. More critically, it enables an attacker to abuse a forwarded agent for logging on to another server without the user's knowledge (CVE Details).

The vulnerability was fixed in Dropbear version 2022.82 by adding a new client option '-o DisableTrivialAuth' to prevent the server from immediately accepting successful authentication before any auth request. This option helps prevent UI confusion and security issues with agent forwarding. Users are recommended to upgrade to version 2022.82 or later (Dropbear Release).