# CVE-2021-4209: gnutls28: A NULL pointer dereference flaw was found in GnuTLS

CVE-2021-4209 is fixed in 7 products on 1 platform, first by gnutls-bin 3.5.18-1ubuntu1.6, released August 1, 2022. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-4209
- Priority: Routine
- CVSS: 6.5 (medium)
- EPSS: 0.0191
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Feb 22, 2022

## Description

A NULL pointer dereference flaw was found in GnuTLS. As Nettle's hash update functions internally call memcpy, providing zero-length input may cause undefined behavior. This flaw leads to a denial of service after authentication in rare circumstances.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | gnutls-bin Ubuntu 18.04.6 LTS (bionic) | 3.5.18-1ubuntu1.6 | [gnutls-bin 3.5.18-1ubuntu1.6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-gnutls-bin-3.5.18-1ubuntu1.6.md) | Aug 1, 2022 |
| Linux | gnutls-bin Ubuntu 20.04 LTS (focal) | 3.6.13-2ubuntu1.7 | [gnutls-bin 3.6.13-2ubuntu1.7](https://patchblox.com/security/data/fix/linux/ubuntu-focal-gnutls-bin-3.6.13-2ubuntu1.7.md) | Aug 1, 2022 |
| Linux | gnutls28 Debian 12.15 (bookworm) | 3.7.3-2 | [DEBIAN-CVE-2021-4209](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4209.md) | Aug 24, 2022 |
| Linux | gnutls28 Debian 13.5 (trixie) | 3.7.3-2 | [DEBIAN-CVE-2021-4209](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4209.md) | Aug 24, 2022 |
| Linux | gnutls28 Debian 14 | 3.7.3-2 | [DEBIAN-CVE-2021-4209](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4209.md) | Aug 24, 2022 |
| Linux | guile-gnutls Ubuntu 20.04 LTS (focal) | 3.6.13-2ubuntu1.7 | [guile-gnutls 3.6.13-2ubuntu1.7](https://patchblox.com/security/data/fix/linux/ubuntu-focal-guile-gnutls-3.6.13-2ubuntu1.7.md) | Aug 1, 2022 |
| Linux | libgnutls-dane0 Ubuntu 18.04.6 LTS (bionic) | 3.5.18-1ubuntu1.6 | [libgnutls-dane0 3.5.18-1ubuntu1.6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libgnutls-dane0-3.5.18-1ubuntu1.6.md) | Aug 1, 2022 |
| Linux | libgnutls-dane0 Ubuntu 20.04 LTS (focal) | 3.6.13-2ubuntu1.7 | [libgnutls-dane0 3.6.13-2ubuntu1.7](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libgnutls-dane0-3.6.13-2ubuntu1.7.md) | Aug 1, 2022 |
| Linux | libgnutls-openssl27 Ubuntu 18.04.6 LTS (bionic) | 3.5.18-1ubuntu1.6 | [libgnutls-openssl27 3.5.18-1ubuntu1.6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libgnutls-openssl27-3.5.18-1ubuntu1.6.md) | Aug 1, 2022 |
| Linux | libgnutls-openssl27 Ubuntu 20.04 LTS (focal) | 3.6.13-2ubuntu1.7 | [libgnutls-openssl27 3.6.13-2ubuntu1.7](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libgnutls-openssl27-3.6.13-2ubuntu1.7.md) | Aug 1, 2022 |
| Linux | libgnutls30 Ubuntu 18.04.6 LTS (bionic) | 3.5.18-1ubuntu1.6 | [libgnutls30 3.5.18-1ubuntu1.6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libgnutls30-3.5.18-1ubuntu1.6.md) | Aug 1, 2022 |
| Linux | libgnutls30 Ubuntu 20.04 LTS (focal) | 3.6.13-2ubuntu1.7 | [libgnutls30 3.6.13-2ubuntu1.7](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libgnutls30-3.6.13-2ubuntu1.7.md) | Aug 1, 2022 |
| Linux | libgnutlsxx28 Ubuntu 18.04.6 LTS (bionic) | 3.5.18-1ubuntu1.6 | [libgnutlsxx28 3.5.18-1ubuntu1.6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libgnutlsxx28-3.5.18-1ubuntu1.6.md) | Aug 1, 2022 |
| Linux | libgnutlsxx28 Ubuntu 20.04 LTS (focal) | 3.6.13-2ubuntu1.7 | [libgnutlsxx28 3.6.13-2ubuntu1.7](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libgnutlsxx28-3.6.13-2ubuntu1.7.md) | Aug 1, 2022 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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