CVE-2026-27145— Inefficient candidate hostname parsing in crypto/x509
Possible ATT&CK Techniques 1AI
T1496 · Resource HijackingAffected Version Matrix 2
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| 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: NVD (National Vulnerability Database)
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: NVD (National Vulnerability Database)
CVSS Information
N/A
Source: NVD (National Vulnerability Database)
Vulnerability Type
N/A
Source: NVD (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
| # | POC Description | Source Link | Shenlong Link |
|---|
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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
- CVE-2026-32280
Unexpected work during chain building in crypto/x509 - CVE-2026-32281
Inefficient policy validation in crypto/x509 - CVE-2026-33810
Case-sensitive excludedSubtrees name constraints cause Auth - CVE-2026-27138
Panic in name constraint checking for malformed certificates - CVE-2026-27137
Incorrect enforcement of email constraints in crypto/x509
Same vendor: Go standard library
- CVE-2026-42504
Quadratic complexity in WordDecoder.DecodeHeader in mime - CVE-2026-42507
Arbitrary inputs are included in errors without any escaping - CVE-2026-39823
Bypass of meta content URL escaping causes XSS in html/templ - CVE-2026-39820
Quadratic string concatentation in consumeComment in net/mai - CVE-2026-42499
Quadratic string concatenation in consumePhrase in net/mail
V. Comments for CVE-2026-27145
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