CVE-2026-39831Network attack vector

Authentication bypass via unchecked user-presence flag

Published May 22, 2026 · Updated May 22, 2026

Improper authentication in golang.org/x/crypto/ssh before 0.52.0 allows remote attackers to authenticate with touch-free security-key signatures. The skECDSAPublicKey.Verify and skEd25519PublicKey.Verify methods accept signed authenticator data without requiring its User Presence bit. Exploitation requires signing capability for an authorized FIDO/U2F key and removes the intended physical-touch gate; it does not by itself expose the private key.

CVSS severity9.1
Critical
EPSS probability0.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Improper authentication in golang.org/x/crypto/ssh before 0.52.0 allows remote attackers to authenticate with touch-free security-key signatures. The skECDSAPublicKey.Verify and skEd25519PublicKey.Verify methods accept signed authenticator data without requiring its User Presence bit. Exploitation requires signing capability for an authorized FIDO/U2F key and removes the intended physical-touch gate; it does not by itself expose the private key.

The record

CVE
CVE-2026-39831
Published
May 22, 2026
Updated
May 22, 2026
Vendor
golang.org/x/crypto
Product
golang.org/x/crypto/ssh
Classifications
CWE-862, T1078
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 22, 2026CVE publishedPublication date reported by the CVE source.
  2. May 22, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <0.52.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

golang.org/x/crypto · golang.org/x/crypto/sshversion=0 <0.52.0

Published CVSS scores

9.1CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-862Missing Authorization
T1078Valid Accounts

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo