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VulnerabilityPublished

CVE-2026-39831: golang.org/x/crypto/ssh · Authentication Bypass by Spoofing

Affects golang.org/x/crypto/sshSource CVE Database V5

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Not known to be exploited · CVSS 9.1 Critical : upgrade to 0.52.0 as a priority.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score
9.1Critical
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.4% chance of exploitation in 30 days – higher than 41% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 0.52.0
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 22 May 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade golang.org/x/crypto/ssh to 0.52.0.

Affected software

ProductAffectedFixed in
golang.org/x/cryptogolang.org/x/crypto/sshAffected
  • <0.52.0
Fixed in
  • 0.52.0
Gogolang.org/x/crypto/sshpkg:golang/golang.org/x/crypto/sshOther threatsAffected
  • =0
Fixed in–
Gogolang.org/x/crypto/sshpkg:golang/golang.org/x/crypto/sshOther threatsAffected
  • <0.52.0
Fixed in
  • 0.52.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Mitigation can be applied by returning a specific extension in Permissions.Extensions to enforce user presence checks. If you cannot patch yet, implement this mitigation if possible.

Description

A critical authentication bypass vulnerability (CVE-2026-39831) exists in golang.org/x/crypto/ssh affecting FIDO/U2F security key types. The Verify() method fails to check the User Presence flag, allowing signatures generated without physical user interaction to be accepted. This flaw enables unauthorized use of hardware security keys without user touch unless mitigated by a specific extension in Permissions.Extensions. The vulnerability has a high CVSS score of 9.1 and impacts authentication security.

References

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