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Vulnerabilities

Vulnerability · CVE-2026-27145

(*x509.Certificate).VerifyHostname previously called matchHostnames in a loop over all DNS Subject Alternative Name (SAN) entries.

Published Jun 2, 2026 · catalog updated Sep 18, 2026 · (*x509.Certificate).VerifyHostname previously called matchHostnames

Check if you run it

No confirmed exploitation is on record for CVE-2026-27145. EPSS is 0.59%. Act only if a listed version of (*x509.Certificate).VerifyHostname previously called matchHostnames is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title ((*x509.Certificate).VerifyHostname previously called matchHostnames).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium6.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.59%
Remediation
Not established
Affected products
See sources for product scope

(*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 affected version ranges are stored yet. Use the vendor advisory before you decide this record does not apply.

How to fix CVE-2026-27145

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-27145. EPSS is 0.59%. Act only if a listed version of (*x509.Certificate).VerifyHostname previously called matchHostnames is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-606. EPSS 0.59%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Jun 2, 2026 · NIST NVD

    Detected

    (*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 hostname

  2. Sep 18, 2026 · NIST NVD

    Updated

    (*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 hostname

Sources

  • CVE.orgVulnerability recordCVE-2026-27145

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-27145

    30-day exploitation probability 0.6%

    first.org
  • NIST NVDVulnerability recordCVE-2026-27145

    (*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 quadratic

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.