CVE-2026-27145

Inefficient candidate hostname parsing in crypto/x509

Published: Jun 2, 2026Updated: Sep 18, 2026 Sources: CVE List NVDCWE-606

6.5MEDIUM

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.

No summary for this CVE yet.

CVSS Vector Breakdown

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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Weaknesses

CWE-606

Affected Products

Go standard library

oss-project·USaka html/template, net/http, golang standard library, crypto/x509

crypto/x509LibraryLibrary

OSS Libraries / generic-library

Exploitability

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

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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 97 more references View all →

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