CVE-2026-39831 Invoking bypass of FIDO/U2F security keys physical interaction in golang.org/x/crypto/ssh

Critical 9.1 Published 22 May 2026 Updated 22 May 2026

Attackers can bypass physical touch requirements for FIDO/U2F security keys in Go SSH, enabling unattended authentication.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2026-39831?

CVE-2026-39831 is a critical vulnerability in golang.org/x/crypto/ssh, published on 22 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

The Verify() method for FIDO/U2F security key types ([email protected], [email protected]) 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.

Weakness: CWE-862

Which versions are affected by CVE-2026-39831?

3 open source packages ship an affected version, including golang.org/x/crypto. It affects 1 product.

Package	Affected	Fixed in
`golang.org/x/crypto` Go	All versions	`0.52.0`
`golang.org/x/crypto` Go	All versions	`0.52.0`
`golang.org/x/crypto` Go	All versions	`0.52.0`

Products include Golang Crypto.

How do I fix CVE-2026-39831?

Upgrade golang.org/x/crypto to 0.52.0 or later.

Is CVE-2026-39831 being exploited?

There is no known exploitation of CVE-2026-39831 in the wild and no public exploit code.

Sources

Also known as AZL-87173, AZL-87206, AZL-87281, BELL-CVE-2026-39831, CLEANSTART-2026-CE49224, CLEANSTART-2026-CF84977 and 1119 more.