CVE-2026-39821

CVE Details

Release Date:	2026-05-22
Impact:	Important	What is this?

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".

See more information about CVE-2026-39821 from MITRE CVE dictionary and NIST NVD

NOTE: The following CVSS metrics and score provided are preliminary and subject to review.

CVSS v3 metrics

Base Score:	8.2
Vector String:	CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N
Version:	3.1
Attack Vector:	Network
Attack Complexity:	High
Privileges Required:	Low
User Interaction:	None
Scope:	Changed
Confidentiality Impact:	High
Integrity Impact:	High
Availability Impact:	None

Errata information

Platform	Errata	Release Date
Oracle Linux version 8 (git-lfs)	ELSA-2026-30853	2026-06-29
Oracle Linux version 9 (git-lfs)	ELSA-2026-30854	2026-06-29