crypto-x509 up to 1.25.10/1.26.3 on Go VerifyHostname algorithmic complexity

Summaryinfo

A vulnerability labeled as problematic has been found in crypto-x509 up to 1.25.10/1.26.3 on Go. This issue affects the function VerifyHostname. Such manipulation leads to algorithmic complexity. This vulnerability is uniquely identified as CVE-2026-27145. The attack can be launched remotely. No exploit exists. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in crypto-x509 up to 1.25.10/1.26.3 on Go and classified as problematic. Affected by this issue is the function VerifyHostname. The manipulation with an unknown input leads to a algorithmic complexity vulnerability. Using CWE to declare the problem leads to CWE-407. An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached. Impacted is availability. CVE summarizes:

(*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.

This vulnerability is handled as CVE-2026-27145 since 02/17/2026. The exploitation is known to be difficult. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1499 by the MITRE ATT&CK project.

Upgrading to version 1.25.11 or 1.26.4 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2026-1776). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Affected

• Golang Go

Productinfo

Name

• crypto-x509

Version

• 1.25.0
• 1.25.1
• 1.25.2
• 1.25.3
• 1.25.4
• 1.25.5
• 1.25.6
• 1.25.7
• 1.25.8
• 1.25.9
• 1.25.10
• 1.26.0
• 1.26.1
• 1.26.2
• 1.26.3

CPE 2.3info

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CPE 2.2info

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Entryinfo

If you want to get best quality of vulnerability data, you may have to visit VulDB.

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