CVE-2026-39831

Summary

golang.org/x/crypto/ssh: FIDO/U2F security key physical presence check can be bypassed

Severity

critical

CVSS

9.1

EPSS

0.4% (p35)

CWE

CWE-862

Also known as

GHSA-89gr-r52h-f8rx, GO-2026-5019

Published

2026-06-25

Updated

2026-06-25

Advisory details

The Verify() method for FIDO/U2F security key types (sk-ecdsa-sha2-nistp256@openssh.com, sk-ssh-ed25519@openssh.com) did not check the User Presence flag. Signatures generated without physical touch were accepted, allowing unattended use of a hardware security key. To restore the previous behavior, return a "no-touch-required" extension in Permissions.Extensions from PublicKeyCallback.

References

• https://github.com/advisories/GHSA-89gr-r52h-f8rx
• https://nvd.nist.gov/vuln/detail/CVE-2026-39831
• https://go.dev/cl/781662
• https://go.dev/issue/79566
• https://groups.google.com/g/golang-announce/c/a082jnz-LvI
• https://pkg.go.dev/vuln/GO-2026-5019

Related advisories

• CVE-2026-46595 — critical · Go/golang.org/x/crypto/ssh
• CVE-2026-39834 — critical · Go/golang.org/x/crypto/ssh
• CVE-2026-39830 — critical · Go/golang.org/x/crypto/ssh
• CVE-2026-39829 — high · Go/golang.org/x/crypto/ssh
• CVE-2026-46597 — high · Go/golang.org/x/crypto/ssh
• CVE-2026-39827 — medium · Go/golang.org/x/crypto/ssh
• CVE-2026-39835 — medium · Go/golang.org/x/crypto/ssh
• CVE-2026-39828 — medium · Go/golang.org/x/crypto/ssh

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