---
id: CVE-2026-87078
title: >-
  Net::IDN::Punycode versions from 2.302 before 2.590 for Perl leak the output
  buffer on every rejected label in decode_punycode.


  The XS backend allocates the scalar it returns before it validates the input,
  sizing the buffer at twice the…
summary: >-
  Net::IDN::Punycode versions from 2.302 before 2.590 for Perl leak the output
  buffer on every rejected label in decode_punycode.


  The XS backend allocates the scalar it returns before it validates the input,
  sizing the buffer at twice 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-401
product: Net-IDN-Encode
affected:
  - Net-IDN-Encode >= 2.302 < 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-2026-87078'
references:
  - url: >-
      https://github.com/robrwo/Net-IDN-Encode/commit/92572f726e48af5559de4cc8a831463b79dfb217.patch
    label: 9b29abf9-4ab0-4765-b253-1875cd9b441e
  - url: >-
      https://github.com/robrwo/Net-IDN-Encode/commit/edad63e0eeeeb18d93bc6dfe4d9dcdff9c244e1b.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/2026/09/22/13'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-22T12:33:13.035011Z'
ingestedAt: '2026-09-22T08:00:27.699Z'
epss: 0.00653
epssPercentile: 0.49153
---

## Overview

Net::IDN::Punycode versions from 2.302 before 2.590 for Perl leak the output buffer on every rejected label in decode_punycode.

The XS backend allocates the scalar it returns before it validates the input, sizing the buffer at twice the input length. The scalar is released only on the success path, so each of the three croaks that reject a label leaves the scalar and its buffer allocated. Nothing bounds the label length in the to-Unicode direction, since the 63-byte DNS limit is checked only when converting to ASCII.

Only the XS backend is affected.

A sender who supplies invalid labels grows the process by twice the label length per rejected call, with no successful call needed.

## Remediation

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