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


  Neither backend checks that its input is well-formed UTF-8, so a string with
  the UTF-8 flag set ov…
summary: >-
  Net::IDN::Punycode versions before 2.590 for Perl hang, crash or return a
  wrong label via unvalidated malformed UTF-8 in encode_punycode.


  Neither backend checks that its input is well-formed UTF-8, so a string with
  the UTF-8 flag set ov…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-835
  - 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-2026-87082'
references:
  - url: >-
      https://github.com/robrwo/Net-IDN-Encode/commit/0918fb4a951ed5f4494c4cf202419c2842507ea4.patch
    label: 9b29abf9-4ab0-4765-b253-1875cd9b441e
  - url: >-
      https://github.com/robrwo/Net-IDN-Encode/commit/572af0183b3a6294e22c6b509268da09697cf77d.patch
    label: 9b29abf9-4ab0-4765-b253-1875cd9b441e
  - url: >-
      https://github.com/robrwo/Net-IDN-Encode/commit/59dc7f2c605a897bcbfe0ac5eb2b8dbe6792348d.patch
    label: 9b29abf9-4ab0-4765-b253-1875cd9b441e
  - url: >-
      https://github.com/robrwo/Net-IDN-Encode/commit/accb6df57ad107ec0c4bfb27b21551eed97c700e.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/2026/09/22/17'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-22T15:07:50.514781Z'
ingestedAt: '2026-09-22T08:00:27.697Z'
epss: 0.00684
epssPercentile: 0.5052
---

## Overview

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

Neither backend checks that its input is well-formed UTF-8, so a string with the UTF-8 flag set over malformed bytes, as the :utf8 PerlIO layer produces from any malformed input, reaches the encoder unchecked. On perl 5.32 and later the XS backend reports a malformed sequence with a length of `(STRLEN)-1`, so the scan steps back one byte instead of forward and never ends. On earlier perls the XS returns a valid label for a different name. The pure-Perl backend runs a regex over the flagged string. Depending on the bytes, it aborts with SIGBUS on perl 5.28 and later, dies with a panic, or returns a wrong label.

The documented conversion functions match the label against Unicode properties first and that match dies on such a string, so only a direct call to encode_punycode reaches the defect. The decoder is not affected.

A direct caller encoding attacker-supplied bytes hangs, crashes or gets a label for a name the input never held.

## Remediation

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