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National Vulnerability Database

National Vulnerability Database

NVD

National Vulnerability Database
  1. Vulnerabilities

CVE-2026-39821 Detail

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".


Metrics

 
NVD enrichment efforts reference publicly available information to associate vector strings. CVSS information contributed by other sources is also displayed.
CVSS 4.0 Severity and Vector Strings:

NIST CVSS score
NIST: NVD
N/A
NVD assessment not yet provided.

References to Advisories, Solutions, and Tools

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URL Source(s) Tag(s)
https://go.dev/cl/767220 Go Project
https://go.dev/issue/78760 Go Project
https://groups.google.com/g/golang-announce/c/iI-mYSI0lu8 Go Project
https://pkg.go.dev/vuln/GO-2026-5026 Go Project

Weakness Enumeration

CWE-ID CWE Name Source
CWE-1289 Improper Validation of Unsafe Equivalence in Input CISA-ADP  

Change History

2 change records found show changes

Quick Info

CVE Dictionary Entry:
CVE-2026-39821
NVD Published Date:
05/22/2026
NVD Last Modified:
05/22/2026
Source:
Go Project