Improper Validation of Unsafe Equivalence in Input Affecting ecs-init package, versions <0:1.105.0-1.amzn2023


Severity

Recommended
0.0
high
0
10

Based on Amazon Linux security rating.

Threat Intelligence

EPSS
0.66% (48th percentile)

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  • Snyk IDSNYK-AMZN2023-ECSINIT-17887304
  • published8 Jul 2026
  • disclosed22 May 2026

Introduced: 22 May 2026

CVE-2026-39821  (opens in a new tab)
CWE-1289  (opens in a new tab)

How to fix?

Upgrade Amazon-Linux:2023 ecs-init to version 0:1.105.0-1.amzn2023 or higher.
This issue was patched in ALAS2023-2026-1902.

NVD Description

Note: Versions mentioned in the description apply only to the upstream ecs-init package and not the ecs-init package as distributed by Amazon-Linux. See How to fix? for Amazon-Linux:2023 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".

References

CVSS Base Scores

version 3.1