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CryptoApplication · Golang

CVE-2026-39831

CRITICAL · 9.1 CVSS v3.1 Published 2026-05-22
Fix available
A fix is available. Upgrade to 0.52.0 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
The Verify() method for FIDO/U2F security key types ([email protected], [email protected]) 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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

OpenSSH's Verify() method for FIDO/U2F security key types ([email protected] and [email protected]) failed to validate the User Presence flag, allowing signatures to be accepted without physical touch of the security key. This critical flaw enables unattended use of hardware security keys, completely undermining their physical authentication guarantee.

MitigationApply the vendor patch to restore proper User Presence flag verification, or if using a custom implementation, ensure the Verify() method returns the 'no-touch-required' extension in Permissions.Extensions from PublicKeyCallback to explicitly indicate when touch is not required.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
CryptoApplication
Affected:< 0.52.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check Golang crypto library version
    Run 'go list -m all | grep golang.org/x/crypto' or check go.mod for 'golang.org/x/crypto' version entry
    Affected if The version is less than 0.52.0 (e.g., 0.51.0, 0.50.0, etc.)
  2. Verify OpenSSH uses FIDO/U2F security keys
    Check SSH configuration files (~/.ssh/authorized_keys) for key types containing 'sk-' prefix such as '[email protected]' or '[email protected]'
    Affected if Any authorized_keys entries use the sk-* FIDO/U2F key types
  3. Confirm FIDO/U2F key is hardware-backed
    Inspect the full public key blob in authorized_keys or run 'ssh-keygen -l -f <public_key_file>' to verify it is a FIDO/WebAuthn security key (look for 'ontoken' or 'resident' indicators in key comments)
    Affected if The key is a hardware security key (not a software/mock implementation)
  4. Check if OpenSSH binary links to vulnerable crypto library
    Run 'ldd $(which ssh) | grep crypto' or 'otool -L $(which ssh) | grep crypto' on macOS to check linked crypto library version, or inspect the Go application's dependencies
    Affected if The linked or bundled golang.org/x/crypto library version is below 0.52.0

You are affected if your environment uses Golang Crypto version below 0.52.0 with OpenSSH configured to accept FIDO/U2F hardware security key authentication using [email protected] or [email protected] key types.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 0.52.0 or later
Fixed in 0.52.0
Interim mitigation

Apply the vendor patch to restore proper User Presence flag verification, or if using a custom implementation, ensure the Verify() method returns the 'no-touch-required' extension in Permissions.Extensions from PublicKeyCallback to explicitly indicate when touch is not required.

Recommended fix High confidence

golang.org/x/crypto v0.52.0 or later

  1. Update the golang.org/x/crypto dependency to version 0.52.0 or later by running: go get golang.org/x/[email protected]
  2. Run go mod tidy to update go.mod and go.sum files
  3. Verify the update by running: go list -m golang.org/x/crypto
  4. Rebuild and test the application to ensure the upgrade does not break existing functionality
Caveat Applications relying on the previous behavior (accepting signatures without user presence) must now explicitly return a 'no-touch-required' extension in Permissions.Extensions from PublicKeyCallback to maintain that behavior

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Crypto Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing8.0 h
  • Review / QA3.0 h
20.0 hours of engineering $3,420
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-39831 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data