dbcve.org
CryptoApplication · Golang

CVE-2026-39835

MEDIUM · 5.3 CVSS v3.1 Published 2026-05-22
Fix available
A fix is available. Upgrade to 0.52.0 or later.
See remediation →
62/100
Remediation priority · Elevated
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
SSH servers which use CertChecker as a public key callback without setting IsUserAuthority or IsHostAuthority could be caused to panic by a client presenting a certificate. CertChecker now returns an error instead of panicking when these callbacks are nil.

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

SSH servers using the CertChecker public key callback in golang.org/x/crypto/ssh without properly setting IsUserAuthority or IsHostAuthority callbacks would panic when a client presented a certificate. The fix modifies CertChecker to return an error instead of panicking when these required callbacks are nil.

MitigationAdministrators and developers using CertChecker in SSH server implementations must ensure IsUserAuthority and IsHostAuthority callbacks are properly configured before deploying to production.

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
None
Integrity
None
Availability
Low

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

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 installed golang.org/x/crypto version
    Run 'go list -m golang.org/x/crypto' or 'go list -m all | grep crypto' in your project directory, or inspect your go.mod file for the crypto module version
    Affected if The version is below 0.52.0
  2. Identify if CertChecker is used in SSH server configuration
    Search your codebase for 'CertChecker' usage in SSH server setup code - look for patterns like 'ssh.ServerConfig{PublicKeyCallback: ...}' where CertChecker is passed
    Affected if CertChecker is used as the PublicKeyCallback function
  3. Check if IsUserAuthority callback is nil
    Inspect the CertChecker instance in your code: verify if the IsUserAuthority field is assigned a non-nil function (e.g., look for 'IsUserAuthority: func(...) bool { ... }')
    Affected if IsUserAuthority is not set (nil) and client certificates may be presented
  4. Check if IsHostAuthority callback is nil
    Inspect the CertChecker instance: verify if the IsHostAuthority field is assigned a non-nil function
    Affected if IsHostAuthority is not set (nil) and client certificates may be presented
  5. Test for panic condition
    If CertChecker is used with nil IsUserAuthority/IsHostAuthority, attempt an SSH connection using certificate-based authentication - observe if the server panics
    Affected if Server panics when a client authenticates with a certificate

You are affected if you use golang.org/x/crypto version below 0.52.0 with CertChecker as a public key callback where either IsUserAuthority or IsHostAuthority is not set (nil) and clients may authenticate using SSH certificates.

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

Administrators and developers using CertChecker in SSH server implementations must ensure IsUserAuthority and IsHostAuthority callbacks are properly configured before deploying to production.

Recommended fix High confidence

golang.org/x/crypto v0.52.0

  1. Update the golang.org/x/crypto dependency to version 0.52.0 or later in go.mod (e.g., run: go get golang.org/x/[email protected])
  2. Run go mod tidy to update all dependencies
  3. Rebuild the application to incorporate the fixed library version
  4. Test that SSH certificate authentication still functions correctly after the upgrade
Caveat The change converts a panic into a returned error when IsUserAuthority or IsHostAuthority callbacks are nil; any existing code relying on the panic behavior will need to handle the error instead

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

Fix this in Crypto Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.

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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-2026-39835 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
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  • Version or environment caveats, and links to real fixes
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