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GO-2026-4599 BIT-golang-2026-27137 CVE-2026-27137

Incorrect enforcement of email constraints in crypto/x509

High Go
Severity
7.5 / 10
High · CVSS 3.1
Exploit chance (EPSS)
0.63%
Chance of exploitation in the next 30 days. Higher than 50.21% of scored vulnerabilities.
Known exploited
No
Not in CISA's catalog
Weakness
CWE-295 Improper Certificate Validation
Fix
1.26.1
Upgrade stdlib to this version or later

Description

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.

Affected versions

Go

PackageVulnerableFixed in
stdlib
>= 1.26.0-0, < 1.26.1
1.26.1

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

stdlib Go → 1.26.1

go
go get stdlib@v1.26.1 && go mod tidy

Severity breakdown

CVSS 3.1 7.5

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

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Weakness

CWE-295: Improper Certificate Validation

The product does not validate, or incorrectly validates, a certificate.

How to prevent it
  • Architecture and Design, Implementation: Certificates should be carefully managed and checked to assure that data are encrypted with the intended owner's public key.
  • Implementation: If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the hostname.

References

Advisories

Fixes and patches

Issue reports

Other links

Timeline

  1. Published
  2. Last updated by the source
  3. Latest EPSS score
AdvisorySeverityWhy it's related
GHSA-4374-p667-p6c8
HTTP/2 rapid reset can cause excessive work in net/http
High Known exploited Also affects stdlib
CVE-2020-0601
Certificate validation bypass on Windows in crypto/x509
High Known exploited Also affects stdlib
RUSTSEC-2026-0382
Distrust compromised intermediate certificates in crypto/x509
Medium Also affects stdlib
GO-2026-6613
HTTP/1 server connection desynchronization after 2xx CONNECT response in net/http
High Also affects stdlib
GO-2026-6609
Lack of limit on size of parsed Range headers in net/http
High Also affects stdlib
GO-2026-6608
Memory limit bypass when parsing MIME headers in net/textproto, mime/multipart
High Also affects stdlib
GO-2026-6607
Reject malformed ECH outer extension references in crypto/tls
High Also affects stdlib
GO-2026-6604
Root.Mkdir(All) can follow junctions out of the root on Windows in os
Critical Also affects stdlib

Credits: Jakub Ciolek

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