CVE-2026-39821

Published May 22, 2026

Last updated 18 hours ago

CVSS critical 9.6
Container Security

Overview

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
security@golang.org
NVD status
Modified
Products
net

Risk scores

CVSS 3.1

Type
Secondary
Base score
9.6
Impact score
5.8
Exploitability score
3.1
Vector string
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N
Severity
CRITICAL

Weaknesses

134c704f-9b21-4f2e-91b3-4a467353bcc0
CWE-1289
0b0ca135-0b70-47e7-9f44-1890c2a1c46c
CWE-1289

Social media

Hype score
Not currently trending

Configurations

References

Sources include official advisories and independent security research.