Inefficient candidate hostname parsing in crypto/x509

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Summary

CVECVE-2026-27145
StatePUBLISHED
AssignerGo
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-02 23:16:35 UTC
Updated2026-06-04 16:15:50 UTC
Description(*x509.Certificate).VerifyHostname previously called matchHostnames in a loop over all DNS Subject Alternative Name (SAN) entries. This caused strings.Split(host, ".") to execute repeatedly on the same input hostname. With a large DNS SAN list, verification costs scaled quadratically based on the number of SAN entries multiplied by the hostname's label count. Because x509.Verify validates hostnames before building the certificate chain, this overhead occurred even for untrusted certificates.

Risk And Classification

Primary CVSS: v3.1 6.5 MEDIUM from ADP

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

EPSS: 0.000110000 probability, percentile 0.015380000 (date 2026-06-09)

Problem Types: CWE-407: Inefficient Algorithmic Complexity

VersionSourceTypeScoreSeverityVector
3.1ADPDECLARED6.5MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
3.1134c704f-9b21-4f2e-91b3-4a467353bcc0Secondary6.5MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
High

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Go Standard Library Crypto/x509 affected 1.25.11 semver Not specified
CNA Go Standard Library Crypto/x509 affected 1.26.0-0 1.26.4 semver Not specified

References

ReferenceSourceLinkTags
go.dev/cl/783621 [email protected] go.dev
pkg.go.dev/vuln/GO-2026-5037 [email protected] pkg.go.dev
go.dev/issue/79694 [email protected] go.dev
groups.google.com/g/golang-announce/c/tKs3rmcBcKw [email protected] groups.google.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Jakub Ciolek - https://ciolek.dev/ (en)

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