CVE-2026-39821 Affecting kubo package, versions <0.41.0-r5


Severity

Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

EPSS
0.05% (16th percentile)

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  • Snyk IDSNYK-CHAINGUARDLATEST-KUBO-17186008
  • published5 Jun 2026
  • disclosed22 May 2026

Introduced: 22 May 2026

NewCVE-2026-39821  (opens in a new tab)

How to fix?

Upgrade Chainguard kubo to version 0.41.0-r5 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kubo package and not the kubo package as distributed by Chainguard. See How to fix? for Chainguard relevant fixed versions and status.

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".

CVSS Base Scores

version 3.1