What is CVE-2026-39831?

CVE-2026-39831 is a critical-severity vulnerability in Golang Crypto, classified under Missing Authorization. CVSS score: 9.1/10. Published 2026-05-22.

How severe is CVE-2026-39831?

Critical severity. CVSS v3 base score is 9.1 out of 10.

Auth bypass in Golang Crypto

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.

Vulnerability class: Broken Access Control

Published 2026-05-22 · last modified 2026-07-23.

CVSS v3 metric

CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.

EPSS exploit prediction

EPSS: 0.005 (40.5th percentile), scored 2026-10-19.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 41st percentile — 40.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.005 · change: +0.001

Affected products

Golang Crypto
Golang.org/x/crypto Golang.org/x/crypto/ssh — versions 0

Weakness classification (CWE)

CWE-862 — Missing Authorization

References

go.dev/issue/79566 (Issue Tracking)
groups.google.com/g/golang-announce/c/a082jnz-LvI (Mailing List)
go.dev/cl/781662 (Issue Tracking)
pkg.go.dev/vuln/GO-2026-5019 (Vendor Advisory)

Frequently asked questions

What is CVE-2026-39831?: CVE-2026-39831 is a critical-severity vulnerability in Golang Crypto, classified under Missing Authorization. CVSS score: 9.1/10. Published 2026-05-22.
How severe is CVE-2026-39831?: Critical severity. CVSS v3 base score is 9.1 out of 10.