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CVE Record

CVE-2026-42508: Invoking auth bypass via unenforced @revoked status in golang.org/x/crypto/ssh/knownhosts

Previously, a revoked 'SignatureKey' belonging to a CA was not correctly checked for revocation. Now, both the 'key' and 'key.SignatureKey' are checked for @revoked.

CriticalCVSS 9.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A flaw in a widely used Go SSH library let revoked certificate authority keys still be trusted when verifying hosts. In practice, if an organization revoked a signing key to cut off compromised or retired infrastructure, Go-based SSH clients could keep accepting connections signed by it. This undermines the trust model that revocation is supposed to guarantee for automated systems and administrative tooling.

Executive priority

Treat as a high-priority patch cycle item, not an emergency. No active exploitation is reported, but the CVSS 9.1 rating and broad Red Hat errata list mean many enterprise Go workloads need updates. Schedule remediation in the current sprint and confirm coverage of internally built Go services and third-party appliances that embed Go SSH tooling.

Technical view

The golang.org/x/crypto/ssh/knownhosts package failed to evaluate the @revoked marker against a certificate's SignatureKey (the CA that signed the presented cert). Only the direct key was checked, so a host certificate signed by a revoked CA still passed verification. The fix now checks @revoked status for both key and key.SignatureKey. Classified CWE-295 (improper certificate validation), CVSS 9.1 (AV:N/AC:L/PR:N/UI:N/C:H/I:H/A:N).

Likely exposure

Applies to Go programs that import golang.org/x/crypto/ssh/knownhosts and rely on a known_hosts file with @revoked entries for CA keys. Common in SSH clients, automation, CI/CD runners, provisioning tools, and infrastructure agents written in Go. Red Hat has shipped errata (RHSA-2026:36796, 37072, 35833, and others) for platform components that embed this library.

Exploitation context

No public exploitation, no proof-of-concept, and no KEV entry is cited in the bundle. Exploitation is conditional: an attacker must control a host key signed by a previously trusted-then-revoked CA and reach a Go SSH client that trusts that CA through knownhosts. Impact is confidentiality and integrity (spoofed server, potential man-in-the-middle), with no availability impact per the CVSS vector.

Researcher notes

Root cause is a missed check in ssh/knownhosts: revocation was evaluated on the presented key but not on its signing CA (key.SignatureKey), defeating the @revoked marker for CA entries. This is a trust-boundary bug (CWE-295) rather than a memory-safety or crypto-primitive weakness. Watch for downstream projects that vendor x/crypto; a rebuild is required even if go.mod is updated. Cross-reference GO-2026-5021 and Red Hat VEX data for authoritative affected-component lists.

Mitigation direction

  • Upgrade golang.org/x/crypto to the fixed release noted in GO-2026-5021 and rebuild dependent binaries.
  • Apply Red Hat errata (RHSA-2026:36796, 37072, 35833, 37123, 36808) on affected RHEL components.
  • Inventory internal Go binaries and agents that import ssh/knownhosts and prioritize patch rollout.
  • Where patching is delayed, avoid relying solely on @revoked CA entries; rotate trusted CA keys instead.
  • Confirm no shadow copies of the vulnerable module remain via vendored dependencies or vendor directories.

Validation and detection

  • Run govulncheck against Go builds to confirm GO-2026-5021 no longer flags the binary.
  • Diff go.sum before and after upgrade to verify golang.org/x/crypto reached the patched version.
  • For RHEL hosts, verify rpm -q reports the errata-patched package build.
  • Test with a known_hosts file that marks a CA @revoked and confirm the client rejects a cert signed by it.
  • Re-scan container images and SBOMs to ensure no legacy x/crypto version ships in production artifacts.
Prepared
Confidence
high
Sources
12

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

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-295: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2026-42508 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.1 (3.1)
Known Exploited
No
Published

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

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
21Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: total

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
9.1CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N3.95.2CISA-ADP
7.4CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N2.25.2redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

9.1Critical
CVSS 3.1 vector shape for CVE-2026-42508Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

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/knownhosts: golang: golang.org/x/crypto/ssh/knownhosts: Revocation bypass via unchecked SignatureKey
other:Red Hat severity ratingcvssV3_1
  • 2026-05-22T04:01:49.515Z: Reported to Red Hat.
  • 2026-05-22T02:31:27.644Z: Made public.

Source materials

Affected products

Products and packages named in the record

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

CWE details

CWE-295

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

CWE-295 · source CWE mapping

Improper Certificate Validation

Improper Certificate Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs