---
title: "CVE-2026-39831: golang.org/x/crypto: FIDO/U2F security key physical presence check can be bypassed"
url: https://erroneo.us/security/cve/CVE-2026-39831/
description: "CVE-2026-39831 (golang.org/x/crypto (Go)): The Verify() method for FIDO/U2F security key types (sk-ecdsa-sha2-nistp256@openssh.com…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-05-22
date_modified: 2026-07-07
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-39831"
kev: false
cvss: 9.1
epss: 0.00487
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-39831: golang.org/x/crypto: FIDO/U2F security key physical presence check can be bypassed

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.5% , percentile 41: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 41% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes golang.org/x/crypto (Go) < 0.52.0, fixed in 0.52.0 . Check your lockfile, including transitive dependencies.

## What it is

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 packages

- Go `golang.org/x/crypto` < 0.52.0 → fixed: 0.52.0

## Affected products (CVE record)

- golang.org/x/crypto golang.org/x/crypto/ssh: < 0.52.0

## Severity

- CISA-ADP CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`
- GitHub CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.49% probability of exploitation activity in the next 30 days; percentile 41.

## Sources

- [GitHub Advisory GHSA-89gr-r52h-f8rx](https://github.com/advisories/GHSA-89gr-r52h-f8rx)
- [CVE.org record CVE-2026-39831](https://www.cve.org/CVERecord?id=CVE-2026-39831)
- [NVD entry CVE-2026-39831](https://nvd.nist.gov/vuln/detail/CVE-2026-39831)
- [go.dev](https://go.dev/issue/79566)
- [groups.google.com](https://groups.google.com/g/golang-announce/c/a082jnz-LvI)
- [go.dev](https://go.dev/cl/781662)
- [pkg.go.dev](https://pkg.go.dev/vuln/GO-2026-5019)

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Source page: https://erroneo.us/security/cve/CVE-2026-39831/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt