CVE-2026-39821

CRITICAL SEVERITY

CVSS Score & Metrics

Base Score

10.0 / 10

Vector String

                                        CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N                                    

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".

Vulnerability Details

Published Date

May 22, 2026

Last Modified

May 29, 2026

CWE ID

CWE-1289

Source

NVD

Vendor

golang

Product

net

External References

https://go.dev/cl/767220
https://go.dev/issue/78760
https://groups.google.com/g/golang-announce/c/iI-mYSI0lu8
https://pkg.go.dev/vuln/GO-2026-5026

CVE-2026-39821

CVSS Score & Metrics

Vulnerability Description

Vulnerability Details

External References

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