🛡️ CVE-2026-39821
🔴 CVSS 9.6 — Critical ✅ No Known Exploit NVD
9.6
CVSS Score
0 Low4 Medium7 High9 Critical10

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".

Details

Severity Critical
CVSS Score 9.6
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N
CWE N/A
Public Exploit ✅ No
Source NVD
Published 2026-05-22
Updated 2026-06-05
Modified 2026-06-04

Affected Packages

Software From version Fixed in
golang.org/x/net — —
net — 0.55.0
unknown — —

Similar Threats

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