---
id: CVE-2026-87080
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.


  The pure-Perl decoder reads one digit at a time with four-argument substr and
  tests the…
summary: >-
  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…
severity: critical
cvss: 9.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H'
cwe:
  - CWE-1286
product: Net-IDN-Encode
affected:
  - Net-IDN-Encode < 2.590
published: '2026-09-22'
updated: '2026-09-22'
sourceUpdated: '2026-09-22T19:07:00.983'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-87080'
references:
  - url: >-
      https://github.com/robrwo/Net-IDN-Encode/commit/48436c7ad2c4d4c6398110e11133754fc476a783.patch
    label: 9b29abf9-4ab0-4765-b253-1875cd9b441e
  - url: 'https://metacpan.org/release/PJCJ/Net-IDN-Encode-2.590-TRIAL/changes'
    label: 9b29abf9-4ab0-4765-b253-1875cd9b441e
  - url: 'http://www.openwall.com/lists/oss-security/2026/09/22/15'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-09-22T15:22:56.999361Z'
ingestedAt: '2026-09-22T08:00:27.698Z'
epss: 0.00632
epssPercentile: 0.481
---

## Overview

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

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.