CVE-2026-87080

Net::IDN::Punycode::PP versions before 2.590 for Perl decode a truncated label to a name containing a character it never encoded in decode_punycode

Published Sep 22, 2026 CVSS 3.1 · 9.1 Critical EPSS < 1% KEV · Not listed
Description
Net::IDN::Punycode::PP versions before 2.590 for Perl decode a truncated label to a name containing a character it never encoded in decode_punycode.

The pure-Perl decoder reads one digit at a time with four-argument substr and tests the result with defined to detect the end of the input. substr on an exhausted string returns the empty string rather than undef, so decoding continues past the end. The empty string converts to a digit value below the range, reducing the accumulator, and the decoder derives one extra code point and its position from it. The result is deterministic. The XS backend rejects the same label.

Net::IDN::Punycode uses this backend wherever the XS does not build.

The two backends disagree about what such a label means, so a sender can pick a label that one installation resolves to a name and another rejects.

Remediation

Vendor Solution

Upgrade to Net-IDN-Encode 2.590-TRIAL or later.

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
First Time appeared Perl
Perl net::idn::punycode
Vendors & Products Perl
Perl net::idn::punycode
Type Values Removed Values Added
References
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 9.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H'}

Type Values Removed Values Added
Description Net::IDN::Punycode::PP versions before 2.590 for Perl decode a truncated label to a name containing a character it never encoded in decode_punycode. The pure-Perl decoder reads one digit at a time with four-argument substr and tests the result with defined to detect the end of the input. substr on an exhausted string returns the empty string rather than undef, so decoding continues past the end. The empty string converts to a digit value below the range, reducing the accumulator, and the decoder derives one extra code point and its position from it. The result is deterministic. The XS backend rejects the same label. Net::IDN::Punycode uses this backend wherever the XS does not build. The two backends disagree about what such a label means, so a sender can pick a label that one installation resolves to a name and another rejects.
Title Net::IDN::Punycode::PP versions before 2.590 for Perl decode a truncated label to a name containing a character it never encoded in decode_punycode
Weaknesses CWE-1286
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
CPANSec
Published
Updated
Sep 22, 2026, 5:07 PM
Reserved
Sep 8, 2026, 7:22 PM
Status
Deferred
Published
Sep 22, 2026, 8:16 AM
Modified
Sep 22, 2026, 7:07 PM