Domain-name confusion via truncated Punycode decoding
Published Sep 22, 2026 · Updated Sep 22, 2026
Input-validation error in Net-IDN-Encode before 2.590 allows attackers to produce inconsistent domain names from truncated Punycode labels. The pure-Perl decode_punycode loop uses four-argument substr but formerly tested only whether its result was defined, so an exhausted string became an empty digit and yielded an extra code point. The condition applies when the XS backend is unavailable, and divergent acceptance can make one installation resolve a name that another rejects.
Summary
What happened
Input-validation error in Net-IDN-Encode before 2.590 allows attackers to produce inconsistent domain names from truncated Punycode labels. The pure-Perl decode_punycode loop uses four-argument substr but formerly tested only whether its result was defined, so an exhausted string became an empty digit and yielded an extra code point. The condition applies when the XS backend is unavailable, and divergent acceptance can make one installation resolve a name that another rejects.
The record
- CVE
- CVE-2026-87080
- Published
- Sep 22, 2026
- Updated
- Sep 22, 2026
- Vendor
- Claus Färber
- Product
- Net-IDN-Encode
- Classifications
- Unavailable
- Attack vector
- Unavailable
- Privileges
- Unavailable
Timeline
How it unfolded
- Sep 22, 2026CVE publishedPublication date reported by the CVE source.
- Sep 22, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=0 <2.590
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Activity data is delayed. The latest report is Sep 28, 2026.
Weakness, pattern, technique
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Public exploit references
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Technologies
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