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CVE-2026-27145

Inefficient candidate hostname parsing in crypto/x509

Published: Jun 2, 2026Updated: Jun 4, 2026 Sources: CVE List NVD
NVD MITRE
6.5CVSSMEDIUM
EPSS Score
0.3%
Top 76.0%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
No Fix Available

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.

CVSS Vector Breakdown

AV:NAC:HPR:NUI:NS:UC:NI:LA:H
Exploitability
AV:NAttack Vector
Network
AC:HAttack Complexity
High
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:LIntegrity
Low
A:HAvailability
High
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Affected Products

crypto/x509Go standard library
Library
OSS Libraries / go
go standard libraryoss-projectUSOSS Librariesaka golang standard library, net/http, crypto/x509, html/template

Exploitability

No known exploits, KEV entries, or remediation guidance available for this vulnerability yet.

References

https://go.dev/cl/783621
go.dev
https://go.dev/issue/79694
go.dev
https://groups.google.com/g/golang-announce/c/tKs3rmcBcKw
groups.google.com
and 1 more references View all →

Timeline

Published
Jun 2, 2026
Last Updated
Jun 4, 2026

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