Vulnerability Report

CVE-2026-27145

Title: Go x509.Certificate.VerifyHostname Quadratic Scaling with Large DNS SANs

Other

Proof Of Concept

PoC Available for CVE-2026-27145

CWE Category NVD-CWE-noinfo

Published Date Jun 02, 2026

Modified Date Jun 04, 2026

Exploit Status Available

Score 6.5 CVSS v

Exploit Probability (EPSS)

0.33%

Vulnerability Summary

CVE-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 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.

Impacted Vendors

Analysis in Progress...

Reference Links

https://go.dev/cl/783621 https://go.dev/issue/79694 https://groups.google.com/g/golang-announce/c/tKs3rmcBcKw https://pkg.go.dev/vuln/GO-2026-5037

CVSS v3.1

Source Entity 134c704f-9b21-4f2e-91b3-4a467353bcc0

Severity MEDIUM

6.5

Attack Vector

NETWORK

Complexity

HIGH

Privileges

N/A

Interaction

NONE

Confidentiality

N/A

Integrity

N/A

Availability

N/A

Scope

UNCHANGED

RAW VECTOR CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H

Associated Attack Patterns (CAPEC)

Total: Patterns

CVE-2026-27145 Exploits & PoCs (Proof Of Concept)

GitHub https://github.com/HORKimhab/CVE-2026-27145

View Code

June 04, 2026 MODIFIED

Vulnerability data updated via NVD.

June 04, 2026 MODIFIED

Vulnerability data updated via NVD.

June 02, 2026 MODIFIED

Vulnerability data updated via NVD.

Attack Vector Matrix

Access Vector NETWORK

Complexity HIGH

Privileges N/A

Interaction NONE

CVSS Vector String


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

Affected Stack

No specific products linked.