---
id: CVE-2026-74766
title: >-
  Net::IDN::Punycode versions from 2.301 before 2.590 for Perl allow a heap
  use-after-free via a decoded code point that reallocates the output buffer in
  decode_punycode.


  The XS backend inserts each decoded code point into the string buff…
summary: >-
  Net::IDN::Punycode versions from 2.301 before 2.590 for Perl allow a heap
  use-after-free via a decoded code point that reallocates the output buffer in
  decode_punycode.


  The XS backend inserts each decoded code point into the string buff…
severity: high
cvss: 8.4
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-416
product: Net-IDN-Encode
affected:
  - Net-IDN-Encode >= 2.301 < 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-2026-74766'
references:
  - url: >-
      https://github.com/robrwo/Net-IDN-Encode/commit/259e74c5739175b063c5393a4ce4a0705678ba61.patch
    label: 9b29abf9-4ab0-4765-b253-1875cd9b441e
  - url: >-
      https://github.com/robrwo/Net-IDN-Encode/commit/2fbc71e4d8517ab65c5d5d35fda086371b735a3f.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: 'https://www.cve.org/CVERecord?id=CVE-2016-15059'
    label: 9b29abf9-4ab0-4765-b253-1875cd9b441e
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-09-22T12:41:49.066140Z'
ingestedAt: '2026-09-22T08:00:27.700Z'
epss: 0.0019
epssPercentile: 0.07647
---

## Overview

Net::IDN::Punycode versions from 2.301 before 2.590 for Perl allow a heap use-after-free via a decoded code point that reallocates the output buffer in decode_punycode.

The XS backend inserts each decoded code point into the string buffer of the scalar it returns. decode_punycode computes the insertion pointer first and only then grows the buffer when the code point does not fit. The growth reallocates the buffer and updates every pointer except the insertion pointer, so the move that follows and the write of the code point go through a freed pointer. The buffer starts at twice the label length, and a code point above U+FFFF takes four bytes in the output, so a label of such code points outgrows it and forces the reallocation.

Version 2.301, the fix for CVE-2016-15059, introduced the defect. Only the XS backend is affected.

Decoding an attacker-supplied punycode label reads and writes freed heap memory.

## Remediation

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