# CVE-2026-39831: Go x/crypto/ssh physical interaction bypass for FIDO/U2F keys

Source: https://junglewise.ai/threats/cve-2026-39831-go-x-crypto-ssh-physical-interaction-bypass-for-fido-u2f-keys  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-22. Updated: 2026-06-25  
License: CC BY 4.0 with a link back

CVE-2026-39831 · Severity: critical · CVSS 9.1 · Published 2026-05-22

A vulnerability in the Go SSH library allows attackers to bypass the physical touch requirement on FIDO/U2F hardware security keys. This means a hardware key could be used to sign in or authorize actions without the owner actually pressing the button on the device. This flaw could lead to unauthorized access to systems or data even when hardware-based multi-factor authentication is enforced.

Technologies: [golang.org/x/crypto (Go)](https://junglewise.ai/threats/technologies/golang-org-x-crypto), [golang.org/x/crypto/ssh (Go)](https://junglewise.ai/threats/technologies/golang-org-x-crypto-ssh). Vendors: [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is CVE-2026-39831 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-39831 being exploited in the wild.

**How severe is CVE-2026-39831?** Critical severity, with a CVSS score of 9.1, published 22 May 2026.

**Which products and versions are affected?** golang.org/x/crypto (Go) SEMVER:introduced=0,fixed=0.52.0; golang.org/x/crypto/ssh (Go) < 0.52.0.

**Is there a fix for CVE-2026-39831?** Yes. golang.org/x/crypto (Go): upgrade to 0.52.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-39831 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-39831?** Check whether you run golang.org/x/crypto (Go) or golang.org/x/crypto/ssh (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- golang.org/x/crypto (Go): upgrade to 0.52.0 or later

  ```sh
  go get golang.org/x/crypto@v0.52.0
  ```


## Technical details

The Verify() method for FIDO/U2F security key types (sk-ecdsa-sha2-nistp256@openssh.com and sk-ssh-ed25519@openssh.com) in golang.org/x/crypto/ssh failed to validate the User Presence (UP) flag in the authenticator data. This allows an attacker or malicious software to utilize a connected hardware security key for SSH authentication without the required physical interaction from the user. The vulnerability is reachable over the network if the library is used in an SSH server or client context. The issue is fixed in version 0.52.0, which restores the check; developers can manually allow touchless operation by returning a 'no-touch-required' extension in Permissions.Extensions.

## Affected products

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

## Identifiers

- CVE-2026-39831
- GHSA-89gr-r52h-f8rx
- GO-2026-5019

## Timeline

- 2026-05-22: disclosed: NVD and Go project initial publication
- 2026-06-25: advisory: GitHub Advisory published
- 2026-06-25: patched: Version 0.52.0 released

## References

- [https://go.dev/cl/781662](https://go.dev/cl/781662)
- [https://go.dev/issue/79566](https://go.dev/issue/79566)
- [https://groups.google.com/g/golang-announce/c/a082jnz-LvI](https://groups.google.com/g/golang-announce/c/a082jnz-LvI)
- [https://pkg.go.dev/vuln/GO-2026-5019](https://pkg.go.dev/vuln/GO-2026-5019)

## Related threats

- [Go SSH deadlock vulnerability in channel handling](https://junglewise.ai/threats/cve-2026-56855-go-ssh-deadlock-vulnerability-in-channel-handling)
- [Go x/crypto/ssh deadlock denial of service on undecided channel](https://junglewise.ai/threats/cve-2026-78662-go-2026-6354-prevent-dos-on-deadlocked-undecided-channel-in)
- [Go SSH source-address permission validation bypass in authentication callbacks](https://junglewise.ai/threats/cve-2026-56854-go-ssh-source-address-permission-validation-bypass-in)
- [GO-2026-5932 - The golang.org/x/crypto/openpgp package is unmaintained, unsafe by design, and has known security issues](https://junglewise.ai/threats/go-2026-5932-the-golang-org-x-crypto-openpgp-package-is-unmaintained-7e8ca4de)
- [Go x/crypto denial of service in SSH agent Ed25519 parsing](https://junglewise.ai/threats/cve-2026-46598-go-x-crypto-denial-of-service-in-ssh-agent-ed25519-parsing)