Privilege Escalation Vulnerability in Golang IDNA Package

CVE-2026-39821

What is CVE-2026-39821?

The ToASCII and ToUnicode functions in Golang's IDNA package fail to properly handle Punycode-encoded labels, allowing for the erroneous acceptance of labels that should trigger errors. This flaw can lead to unintended privilege escalation by accepting input like 'xn--example-.com' and incorrectly processing it as 'example.com', which may bypass privilege checks and grant unauthorized access. Developers using this package should reassess their privilege validation mechanisms to ensure they are not vulnerable to this issue.

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