CVE-2026-39821

Beschreibung

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-.