In short
- CVE-2026-27145 is a MEDIUM (CVSS 6.5) vulnerability affecting stdlib.
- Chance of exploitation in the next 30 days (EPSS): 0.59%, higher than 48.3% of all vulnerabilities.
- Fix: update to 1.26.4, 1.25.11 or later.
| Package | Affected versions | Patched versions |
|---|
| stdlib Go | ≥ 1.26.0-0, < 1.26.4< 1.25.11
| 1.26.41.25.11
|
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.
NVD 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.
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