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Vulnerability record · CVE-2016-20012 · published 15 September 2021

CVE-2016-20012: Openbsd openssh observable discrepancy vulnerability

Openbsd · Openssh

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

5.3 CVSS 3.1 Medium EPSS 5.3% · top 7.7% CWE-203 · Observable discrepancy
5.3CVSS 3.1 base score, v2 4.3
5.3%EPSS exploitation probability, 30 days
NoNot in CISA KEV
5Affected product versions listed by NVD
17References, 5 tagged exploit
17 Jun 2026Last modified by NVD

Description

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

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Affected products

5 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

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

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Source: NIST National Vulnerability Database (record CVE-2016-20012), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.