CVE-2026-87079

Vulnerability Description

Net::IDN::Punycode versions before 2.590 for Perl allow CPU exhaustion via quadratic insertion cost when decoding a long label in decode_punycode. The XS backend inserts each decoded code point into a UTF-8 buffer and finds the insertion point by scanning that buffer from the start, one character at a time. The scan runs once per code point over the output built so far, so the cost is quadratic in the label length. The pure-Perl backend downgrades its input to bytes so that substr can index it directly, but takes its working copy before the downgrade, so when the input carries the UTF-8 flag every substr on the copy scans from the start, with the same quadratic cost. Nothing bounds the label length in the to-Unicode direction. The 63-byte DNS limit is checked only when converting to ASCII, so domain_to_unicode and uts46_to_unicode pass an attacker-supplied label of any length to the decoder.

CVSS Score

Related Weaknesses (CWE)

References

• https://github.com/robrwo/Net-IDN-Encode/commit/00d723423b66810af26b88c552bedc61
• https://github.com/robrwo/Net-IDN-Encode/commit/447c6b38ef5d4570329fa4f78690f4e1
• https://metacpan.org/release/PJCJ/Net-IDN-Encode-2.590-TRIAL/changes
• http://www.openwall.com/lists/oss-security/2026/09/22/14