What’s Vulnerable › Vulnerabilities

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

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-05-22 · updated 2026-07-23
• Weakness: CWE-862

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.

Affected products

• golang.org/x/crypto/ssh: before 0.52.0 — fixed in 0.52.0
• Golang.Org/X/Crypto: before 0.52.0 — fixed in 0.52.0

How to fix

Upgrade to a fixed version: golang.org/x/crypto/ssh 0.52.0; Golang.Org/X/Crypto 0.52.0. Check the vendor advisory for mitigations.

References

• 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

Get alerted when CVE-2026-39831 or the next vulnerability affects your stack