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Critical severity9.1NVD Advisory· Published May 22, 2026· Updated Jun 2, 2026

CVE-2026-39831

CVE-2026-39831

Description

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.

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Affected products

2705

Patches

Vulnerability mechanics

References

4

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