NVD Vulnerability Detail
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CVE-2026-39821
Summary

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".

Publication Date May 23, 2026, 1:16 a.m.
Registration Date May 27, 2026, 4:05 a.m.
Last Update May 23, 2026, 4:17 a.m.
CVSS3.1 : CRITICAL
スコア 10.0
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
攻撃元区分(AV) ネットワーク
攻撃条件の複雑さ(AC)
攻撃に必要な特権レベル(PR) 不要
利用者の関与(UI) 不要
影響の想定範囲(S) 変更あり
機密性への影響(C)
完全性への影響(I)
可用性への影響(A) なし
Related information, measures and tools
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