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Setting MAX_AUTH_TRIES (or -T) to 0 is a valid configuration - it requires the first authentication attempt to succeed.
A ssh client queries a server whether a public key will be accepted prior to performing a real signature. Previously there was no limit on the number of queries. Public key queries are a user enumeration/privacy concern if an attacker iterates with known public keys such as those published by github (mapping to github usernames). If total privacy is required, the proper solution is to use separate authorized_keys compared to publicly used ones (or avoid services that publish public keys). As a mitigation for reused public keys, Dropbear now limits to 15 public keys attempts per session. Public key queries start being counted as failed authentication attempts after (MAX_AUTH_TRIES - MAX_PUBKEY_QUERIES). This provides a rate limit on public key queries. Reported by HD Moore, details are in the SSHamble presentation.
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A ssh client queries a server whether a public key will be accepted
prior to performing a real signature. Previously there was no limit on
the number of queries.
Public key queries are a user enumeration/privacy concern if an attacker
iterates with known public keys such as those published by github
(mapping to github usernames). If total privacy is required, the proper
solution is to use separate authorized_keys compared to publicly used
ones (or avoid services that publish public keys).
As a mitigation for reused public keys, Dropbear now limits to 15 public
keys attempts per session. Public key queries start being counted as
failed authentication attempts after (MAX_AUTH_TRIES - MAX_PUBKEY_QUERIES).
This provides a rate limit on public key queries.
Reported by HD Moore, details are in the SSHamble presentation.