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CVE-2026-27145— Inefficient candidate hostname parsing in crypto/x509

Quick assessment

Affected
Go standard library crypto/x509
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Google Go是美国谷歌（Google）公司的一种静态强类型、编译型、并发型，并具有垃圾回收功能的编程语言。 Google Go存在安全漏洞，该漏洞源于在循环中重复调用strings.Split导致验证成本随DNS SAN条目数量呈二次方增长，即使对不受信任的证书也会产生开销。

AI Predicted 7.5 Difficulty: Trivial EPSS 0.59% · P46

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 2

VendorProduct Version RangeStatus
Go standard library crypto/x509 < 1.25.11 affected
1.26.0-0< 1.26.4 affected
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I. Basic Information for CVE-2026-27145

Vulnerability Information
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Vulnerability Title
Inefficient candidate hostname parsing in crypto/x509
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Google Go 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Google Go是美国谷歌（Google）公司的一种静态强类型、编译型、并发型，并具有垃圾回收功能的编程语言。 Google Go存在安全漏洞，该漏洞源于在循环中重复调用strings.Split导致验证成本随DNS SAN条目数量呈二次方增长，即使对不受信任的证书也会产生开销。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Go standard library crypto/x509 0 ~ 1.25.11 -

II. Public POCs for CVE-2026-27145

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III. Intelligence Information for CVE-2026-27145

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Patches & Fixes for CVE-2026-27145 (1)

Vendor Advisories for CVE-2026-27145 (1)

Vendor Pages for CVE-2026-27145 (2)

Same Patch Batch · Go standard library · 2026-06-02 · 3 CVEs total

CVE-2026-42504 Quadratic complexity in WordDecoder.DecodeHeader in mime
CVE-2026-42507 Arbitrary inputs are included in errors without any escaping in net/textproto

IV. Related Vulnerabilities

Same product: crypto/x509
Same vendor: Go standard library

V. Comments for CVE-2026-27145

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