CVE-2016-20012

Published: 15 September 2021

** DISPUTED ** 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: the vendor does not recognize user enumeration as a vulnerability for this product.

Notes

openssh-ssh1 is provided for compatibility with old devices that
cannot be upgraded to modern protocols. Thus we may not provide security
support for this package if doing so would prevent access to equipment.
The upstream OpenSSH developers see this as an important
security feature and do not intend to 'fix' it.

Reading through the comments in PR 270, which is now closed and has
not been merged, it is possible to see that upstream does not plan
on fixing this issue because it would introduce too many possible
new problems.

Status

Severity score breakdown

References

• https://github.com/openssh/openssh-portable/pull/270
• https://github.com/openssh/openssh-portable/blob/d0fffc88c8fe90c1815c6f4097bc8cbcabc0f3dd/auth2-pubkey.c#L261-L265
• https://rushter.com/blog/public-ssh-keys/
• https://utcc.utoronto.ca/~cks/space/blog/tech/SSHKeysAreInfoLeak
• https://www.cve.org/CVERecord?id=CVE-2016-20012
• NVD
• Launchpad
• Debian