CVE-2026-27145: CWE-407: Inefficient Algorithmic Complexity in Go standard library crypto/x509
Severity: mediumType: VulnerabilityCVE-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.
CVE-2026-27145: CWE-407: Inefficient Algorithmic Complexity in Go standard library crypto/x509
0
MediumPublished: 06/02/2026 (06/02/2026, 22:01:36 UTC)
Source: CVE Database V5
Vendor/Project: Go standard library
Product: crypto/x509
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.
CVSS v3.1
Score 6.5medium
Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
High
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
Affected software
Go standard library
crypto/x509
Affected versions
>=0 <1.25.11>=1.26.0-0 <1.26.4
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Technical Details
- Data Version
- 5.2
- Assigner Short Name
- Go
- Date Reserved
- 2026-02-17T19:57:28.435Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Vendor Advisory Urls
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Threat ID: 6aa3091f91cc7f3848a0178f
Added to database: 09/10/2026, 19:46:39 UTC
Last updated: 09/10/2026, 19:46:39 UTC
Views: 1
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