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CVE Record

CVE-2026-39835: Invoking server panic during CheckHostKey/Authenticate in golang.org/x/crypto/ssh

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.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This vulnerability can let an unauthenticated SSH client crash certain Go-based SSH servers. It affects applications using golang.org/x/crypto/ssh CertChecker in a specific incomplete configuration. The main business risk is service outage, not data theft or direct system takeover based on the provided sources.

Executive priority

Treat as high priority for internet-facing or business-critical Go SSH services. Prioritize inventory first because only a specific certificate-authentication configuration appears exposed. Patch or reconfigure affected services promptly to reduce outage risk.

Technical view

In golang.org/x/crypto/ssh, SSH servers using CertChecker as a public key callback without IsUserAuthority or IsHostAuthority could panic when a client presents a certificate. The issue is CWE-476 with CVSS 7.5, driven by network-reachable, unauthenticated availability impact.

Likely exposure

Exposure is likely limited to custom or embedded Go SSH servers using golang.org/x/crypto/ssh CertChecker for certificate authentication with the authority callbacks unset. Standard SSH deployments are not shown as affected by the supplied evidence.

Exploitation context

The bundle does not show active exploitation, and KEV is false. The described trigger is remote and unauthenticated, but only works against servers with the vulnerable CertChecker configuration. Impact is denial of service through server panic.

Researcher notes

Evidence supports a nil-callback panic in CertChecker during CheckHostKey or Authenticate paths. Confidentiality and integrity impact are not indicated. Exact affected and fixed module versions are not present in the supplied bundle, so validate against GO-2026-5015 or vendor advisories.

Mitigation direction

  • Update golang.org/x/crypto/ssh according to Go vulnerability guidance.
  • Apply relevant Red Hat advisories where downstream packages are affected.
  • Configure CertChecker with appropriate IsUserAuthority or IsHostAuthority callbacks.
  • Check vendor guidance before assuming a fixed version not listed here.

Validation and detection

  • Inventory Go services importing golang.org/x/crypto/ssh.
  • Identify SSH server code using CertChecker as PublicKeyCallback.
  • Verify IsUserAuthority or IsHostAuthority is configured where certificates are accepted.
  • Confirm dependency status against GO-2026-5015 and vendor advisories.
  • Add regression coverage that certificate authentication returns an error, not a panic.
Prepared
Confidence
medium
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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cwe · low confidence lookup

CWE-476: Exact CWE lookup

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cve · low confidence lookup

CVE-2026-39835 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
32Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADP
5.3CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L3.91.4CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-39835Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc
redhat-SADPgolang.org/x/crypto/ssh: golang: golang.org/x/crypto/ssh: Denial of Service via crafted SSH certificate
other:Red Hat severity ratingcvssV3_1
  • 2026-05-22T04:01:27.279Z: Reported to Red Hat.
  • 2026-05-22T02:31:26.982Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
golang.org/x/cryptogolang.org/x/crypto/sshgolang.org/x/crypto/ssh, 0unaffected
Weakness

CWE details

CWE-476

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-476 · source CWE mapping

NULL Pointer Dereference

NULL Pointer Dereference represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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