CVE-2026-39821— Invoking failure to reject ASCII-only Punycode-encoded labels in golang.org/x/net/idna
Possible ATT&CK Techniques 1AI
T1078 · Valid AccountsAffected Version Matrix 1
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| golang.org/x/net | golang.org/x/net/idna | < 0.55.0 | affected |
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I. Basic Information for CVE-2026-39821
Vulnerability Information
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Vulnerability Title
Invoking failure to reject ASCII-only Punycode-encoded labels in golang.org/x/net/idna
Source: NVD (National Vulnerability Database)
Vulnerability Description
The ToASCII and ToUnicode functions incorrectly accept Punycode-encoded labels that decode to an ASCII-only label. For example, ToUnicode("xn--example-.com") incorrectly returns the name "example.com" rather than an error. This behavior can lead to privilege escalation in programs using the idna package. For example, a program which performs privilege checks on the ASCII hostname may reject "example.com" but permit "xn--example-.com". If that program subsequently converts the ASCII hostname to Unicode, it will inadvertently permits access to the Unicode name "example.com".
Source: NVD (National Vulnerability Database)
CVSS Information
N/A
Source: NVD (National Vulnerability Database)
Vulnerability Type
N/A
Source: NVD (National Vulnerability Database)
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ToASCII和ToUnicode函数错误接受解码为纯ASCII标签的Punycode编码标签，可能导致权限提升。
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 |
|---|---|---|---|---|
| golang.org/x/net | golang.org/x/net/idna | 0 ~ 0.55.0 | - |
II. Public POCs for CVE-2026-39821
| # | POC Description | Source Link | Shenlong Link |
|---|
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Patches & Fixes for CVE-2026-39821 (1)
Vendor Advisories for CVE-2026-39821 (3)
Same Patch Batch · golang.org/x/net · 2026-05-22 · 6 CVEs total
| CVE-2026-25680 | Invoking denial of service when parsing arbitrary HTML in golang.org/x/net/html | |
| CVE-2026-25681 | Invoking incorrect handling of character references in DOCTYPE nodes in golang.org/x/net/ | |
| CVE-2026-42502 | Invoking incorrect handling of HTML elements in foreign content in golang.org/x/net/html | |
| CVE-2026-42506 | Invoking incorrect handling of namespaced elements in foreign content in golang.org/x/net | |
| CVE-2026-27136 | Invoking duplicate attributes can cause XSS in golang.org/x/net/html |
IV. Related Vulnerabilities
Same vendor: golang.org/x/net
- CVE-2026-27136
Invoking duplicate attributes can cause XSS in golang.org/x - CVE-2026-25680
Invoking denial of service when parsing arbitrary HTML in go - CVE-2026-25681
Invoking incorrect handling of character references in DOCT - CVE-2026-42502
Invoking incorrect handling of HTML elements in foreign con - CVE-2026-42506
Invoking incorrect handling of namespaced elements in forei
V. Comments for CVE-2026-39821
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