CVE-2026-87082: Net::IDN::Punycode versions before 2.590 for Perl hang, crash or return a wrong label via unvalidated malformed UTF-8 in encode_punycode

CVE-2026-87082 is a denial-of-service and data corruption vulnerability in the Net::IDN::Punycode Perl library. The flaw is triggered when the encode_punycode function processes malformed UTF-8 input passed through the :utf8 PerlIO layer, bypassing necessary validation checks. Depending on the Perl version and backend used, this can cause the library to hang indefinitely, crash with a panic or SIGBUS error, or return a Punycode label for a different domain name than the input. The decoder is not affected, and only direct calls to encode_punycode are vulnerable. As of now, there are no known public proofs-of-concept or reports of in-the-wild exploitation.

Upgrade Net::IDN::Punycode to version 2.590 or later. If you cannot upgrade, avoid passing strings with the :utf8 PerlIO layer that may contain malformed UTF-8 to the encode_punycode function. Ensure any user-supplied input is validated as well-formed UTF-8 before processing.