CVE-2026-39831

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.

  • Published May 22, 2026
  • CVSS 9.1 critical
  • 0.5% chance of exploitation in the next 30 days (EPSS)

Affected software

In the news

CVE-2026-39831 at the National Vulnerability Database