CVE-2026-39821 | BDVDB-2026-334545 Detail

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".

Impact#

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Exploit#

History#

1. Version 12026-05-22Record published in the CVE List.
2. Version 22026-09-17Most recent update recorded in the CVE List.