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CVE Record

CVE-2026-27137: Incorrect enforcement of email constraints in crypto/x509

When verifying a certificate chain which contains a certificate containing multiple email address constraints which share common local portions but different domain portions, these constraints will not be properly applied, and only the last constraint will be considered.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This flaw affects Go's certificate validation library. In a narrow email-certificate case, multiple email constraints can be enforced incorrectly, so validation may rely only on the last matching constraint. Organizations using Go for certificate-chain verification should treat this as important, but the provided sources do not show active exploitation.

Executive priority

Prioritize assessment and patch planning for systems where Go validates certificates for trust decisions. The issue is high severity, but urgency is reduced if the environment does not process email-constrained certificate chains and no exploitation evidence is available.

Technical view

In Go standard library crypto/x509, certificate chains with multiple email address constraints sharing the same local portion but different domains may not apply all constraints. The CVE maps to CWE-295 and CVSS 7.5. The bundle identifies affected package crypto/x509 and version 1.26.0-0, with Go and Red Hat advisories referenced.

Likely exposure

Exposure is most likely in Go applications or bundled products that use crypto/x509 to verify certificate chains involving email address name constraints. The provided bundle does not identify broader affected products beyond Go standard library crypto/x509 and Red Hat advisory tracking.

Exploitation context

The CVE is not listed as KEV in the provided bundle. No cited source in the bundle states active exploitation. Practical impact depends on whether an application validates certificate chains containing the specific email constraint pattern.

Researcher notes

The key behavior is constraint collapse: multiple email constraints with common local portions and different domains may leave only the last constraint effective. Validate against vendor advisories before assigning affected status because the bundle provides limited version detail.

Mitigation direction

  • Review Go advisory GO-2026-4599 and Go announcement for fixed release guidance.
  • Apply relevant vendor updates from Go or Red Hat when applicable.
  • Inventory Go applications that perform certificate-chain verification with crypto/x509.
  • Prioritize externally exposed trust-validation paths and packaged Go runtimes.

Validation and detection

  • Identify deployed Go versions and packaged Go runtime sources.
  • Search dependency and build records for crypto/x509 certificate verification use.
  • Review certificate validation tests covering email name constraints.
  • Confirm applicable Red Hat errata status for managed platforms.
Prepared
Confidence
medium
Sources
9

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.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-27137 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
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
45Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical 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:H3.93.6CISA-ADP
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

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-27137Attack 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-SADPcrypto/x509: Incorrect enforcement of email constraints in crypto/x509
other:Red Hat severity ratingcvssV3_1
  • 2026-03-06T22:01:38.859Z: Reported to Red Hat.
  • 2026-03-06T21:28:13.748Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Go standard librarycrypto/x509crypto/x509, 1.26.0-0unaffected
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.

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