CVE-2026-39821 — Invoking failure to reject ASCII-only Punycode-encoded labels in golang.org/x/net/idna

Affected: Go standard library net/http, Go standard library net/http/internal/http2, golang.org/x/net/idna, Red Hat Ansible Automation Platform 2.5 for RHEL 8, Red Hat Ansible Automation Platform 2.5 for RHEL 9, Red Hat Ansible Automation Platform 2.6 for RHEL 10, Red Hat Ansible Automation Platform 2.6 for RHEL 9, Red Hat Ansible Automation Platform 2.7 for RHEL 10, Red Hat Ansible Automation Platform 2.7 for RHEL 9, Red Hat Enterprise Linux 10 and 139 more

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".

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CVE-2026-39821 — Invoking failure to reject ASCII-only Punycode-encoded labels in golang.org/x/net/idna