CVE-2026-27145mediumCWE-606

CVE-2026-27145: medium-severity vulnerability in Go standard library crypto/x509

Inefficient candidate hostname parsing in crypto/x509

Published 02 Jun 2026 · Updated 18 Sep 2026

33Vexday Risk Score

No sign of exploitation. It has a public proof of concept.

ssvc Attendcvss 6.5epss 0.6%

from disclosure to weapon1 days

Published on NVDJun 2

1st PoC+1d

exploitation probability

0.6%top 53% of all CVEs

observed exploitation

nono source reports it

1 public exploit(s)

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

Affected products

Go standard library · crypto/x509

public PoCs found — 1

githubgithub.com/HORKimhab/CVE-2026-27145★ 0

⚠ Public resources, to assess the exposure of systems you control or are authorized to test. Test only with authorization.

Related CVEs — Go standard library crypto/x509

In the same product, most dangerous first.

CVE-2024-24783MEDIUMVerify panics on certificates with an unknown public key algorithm in crypto/x509EPSS 0.7%CVE-2026-27137HIGHIncorrect enforcement of email constraints in crypto/x509EPSS 0.6%CVE-2026-32280HIGHUnexpected work during chain building in crypto/x509EPSS 0.6%CVE-2025-22865HIGHParsePKCS1PrivateKey panic with partial keys in crypto/x509EPSS 0.6%CVE-2024-45341MEDIUMUsage of IPv6 zone IDs can bypass URI name constraints in crypto/x509EPSS 0.5%CVE-2025-61729HIGHExcessive resource consumption when printing error string for host certificate validation in crypto/x509EPSS 0.5%

References