CVE-2026-39831: golang.org/x/crypto/ssh: FIDO/U2F security key physical presence check can be bypassed

June 25, 2026

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

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

Code Behaviors & Features

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