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CVE-2026-39821 affects the Go package golang.org/x/net/idna. The vulnerability is caused by incorrect handling of certain Punycode-encoded labels by the ToASCII and ToUnicode functions. Specifically, these functions incorrectly accept Punycode labels that decode to an ASCII-only label instead of rejecting them as invalid. For example, ToUnicode("xn--example-.com") incorrectly returns "example.com" rather than an error. This creates a validation and canonicalization inconsistency where one hostname representation may pass checks while another equivalent normalized form maps to a protected ASCII hostname. In applications that perform authorization, access control, or privilege checks on the original ASCII hostname and later convert it to Unicode using the vulnerable idna package, an attacker can exploit this discrepancy to access resources associated with the normalized hostname.
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14 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.
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Every observed campaign linking this CVE to a named adversary.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.