---
id: CVE-2019-12290
title: >-
  GNU libidn2 before 2.2.0 fails to perform the roundtrip checks specified in
  RFC3490 Section 4.2 when converting A-labels to U-labels
summary: >-
  GNU libidn2 before 2.2.0 fails to perform the roundtrip checks specified in
  RFC3490 Section 4.2 when converting A-labels to U-labels. This makes it
  possible in some circumstances for one domain to impersonate another. By
  creating a malic…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N'
cwe:
  - CWE-20
vendor: gnu
product: libidn2
affected:
  - libidn2 < 2.2.0
patched:
  - libidn2 2.2.0
published: '2019-10-22'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T07:16:45.200'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2019-12290'
references:
  - url: 'http://lists.opensuse.org/opensuse-security-announce/2019-12/msg00008.html'
    label: cve@mitre.org
  - url: 'http://lists.opensuse.org/opensuse-security-announce/2019-12/msg00009.html'
    label: cve@mitre.org
  - url: >-
      https://gitlab.com/libidn/libidn2/commit/241e8f486134793cb0f4a5b0e5817a97883401f5
    label: cve@mitre.org
  - url: >-
      https://gitlab.com/libidn/libidn2/commit/614117ef6e4c60e1950d742e3edf0a0ef8d389de
    label: cve@mitre.org
  - url: 'https://gitlab.com/libidn/libidn2/merge_requests/71'
    label: cve@mitre.org
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3UFT76Y7OSGPZV3EBEHD6ISVUM3DLARM/
    label: cve@mitre.org
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/KXDKYWFV6N2HHVSE67FFDM7G3FEL2ZNE/
    label: cve@mitre.org
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ONG3GJRRJO35COPGVJXXSZLU4J5Y42AT/
    label: cve@mitre.org
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RSI4TI2JTQWQ3YEUX5X36GTVGKO4QKZ5/
    label: cve@mitre.org
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/U6ZXL2RDNQRAHCMKWPOMJFKYJ344X4HL/
    label: cve@mitre.org
  - url: 'https://security.gentoo.org/glsa/202003-63'
    label: cve@mitre.org
  - url: 'https://usn.ubuntu.com/4168-1/'
    label: cve@mitre.org
  - url: 'http://lists.opensuse.org/opensuse-security-announce/2019-12/msg00008.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'http://lists.opensuse.org/opensuse-security-announce/2019-12/msg00009.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://gitlab.com/libidn/libidn2/commit/241e8f486134793cb0f4a5b0e5817a97883401f5
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://gitlab.com/libidn/libidn2/commit/614117ef6e4c60e1950d742e3edf0a0ef8d389de
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://gitlab.com/libidn/libidn2/merge_requests/71'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3UFT76Y7OSGPZV3EBEHD6ISVUM3DLARM/
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/KXDKYWFV6N2HHVSE67FFDM7G3FEL2ZNE/
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ONG3GJRRJO35COPGVJXXSZLU4J5Y42AT/
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RSI4TI2JTQWQ3YEUX5X36GTVGKO4QKZ5/
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/U6ZXL2RDNQRAHCMKWPOMJFKYJ344X4HL/
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://security.gentoo.org/glsa/202003-63'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://usn.ubuntu.com/4168-1/'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-398330.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - nvd
epss: 0.03106
epssPercentile: 0.87454
ingestedAt: '2026-10-14T07:21:04.822Z'
---

## Overview

GNU libidn2 before 2.2.0 fails to perform the roundtrip checks specified in RFC3490 Section 4.2 when converting A-labels to U-labels. This makes it possible in some circumstances for one domain to impersonate another. By creating a malicious domain that matches a target domain except for the inclusion of certain punycoded Unicode characters (that would be discarded when converted first to a Unicode label and then back to an ASCII label), arbitrary domains can be impersonated.

## Affected

- `libidn2 < 2.2.0`

## Remediation

Upgrade past the affected range:

- `libidn2 2.2.0`