OpenSSH through 8.7 allows remote attackers, who have a suspicion that a certain combination of username and public key is known to an SSH server, to test whether this suspicion is correct. This occurs because a challenge is sent only when that combination could be valid for a login session. NOTE: t...

References

• https://github.com/openssh/openssh-portable/blob/d0fffc88c8fe90c1815c6f4097bc8cbcabc0f3dd/auth2-pubkey.c#L261-L265
• https://github.com/openssh/openssh-portable/pull/270
• https://github.com/openssh/openssh-portable/pull/270#issuecomment-920577097
• https://github.com/openssh/openssh-portable/pull/270#issuecomment-943909185
• https://rushter.com/blog/public-ssh-keys/
• https://security.netapp.com/advisory/ntap-20211014-0005/
• https://utcc.utoronto.ca/~cks/space/blog/tech/SSHKeysAreInfoLeak
• https://www.openwall.com/lists/oss-security/2018/08/24/1
• https://github.com/openssh/openssh-portable/blob/d0fffc88c8fe90c1815c6f4097bc8cbcabc0f3dd/auth2-pubkey.c#L261-L265
• https://github.com/openssh/openssh-portable/pull/270

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