SEPTEMBER 18, 2026
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Case File

CVE-2026-39821

CRITICAL · CVSS 9.6 EPSS 0.66%

Source: NVD + CISA KEV + EPSS (historical backfill) · Published 2026-05-22 · Last synced 2026-08-04

CyberRota Analysis

This is a critical severity vulnerability with a CVSS score of 9.6. See the original NVD description below for full technical details.

CVE
CVE-2026-39821
Severity
CRITICAL
CVSS
9.6
EPSS
0.66%

Original NVD 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".

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