CVE-2026-27145

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.

How to fix CVE-2026-27145

To remediate CVE-2026-27145, upgrade the affected package to a fixed version below.

• —upgrade to 1.25.11 or later
• —no fix listed
• —no fix listed
• —no fix listed
• —upgrade to 1.25.11-1 or later
• —upgrade to 1.26.4-1 or later
• —upgrade to 1.25.11 or later

Is CVE-2026-27145 being exploited?

Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.

Affected packages (7)

• from 0, < 1.25.11, >= 1.26.0-0, < 1.26.4
• from 0
• from 0
• from 0
• from 0, < 1.25.11-1
• from 0, < 1.26.4-1
• from 0, < 1.25.11, >= 1.26.0-0, < 1.26.4

CVSS scores

References (6)

• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2026-27145
• PATCHgo.dev/cl/783621
• REPORTgo.dev/issue/79694
• WEBgroups.google.com/g/golang-announce/c/tKs3rmcBcKw
• WEBnvd.nist.gov/vuln/detail/CVE-2026-27145