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VulnerabilityPublished Updated

CVE-2026-27137: Go standard library crypto/x509 · Improper Certificate Validation

Affects Go standard library crypto/x509Source CVE Database V5

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Not known to be exploited · CVSS 7.5 High : upgrade to 1.26.1 soon.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score
7.5High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.6% chance of exploitation in 30 days – higher than 50% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 1.26.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 6 Mar 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade Go standard library crypto/x509 to 1.26.1.

Affected software

ProductAffectedFixed in
Go standard librarycrypto/x509Affected
  • >=1.26.0-0 <1.26.1
Fixed in
  • 1.26.1
Gocrypto/x509pkg:golang/crypto/x509Other threatsAffected
  • >=1.26.0-0 <1.26.1
Fixed in
  • 1.26.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Currently, no mitigation is available that meets Red Hat's criteria for ease of use, deployment, or applicability to a widespread installation base. Upgrading to a fixed version of the Go standard library when released is recommended. For affected Red Hat products, consult Red Hat support or your Technical Account Manager for guidance. Avoid relying on partial workarounds that may not fully address the issue.

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.

References

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