# CVE-2021-32749: fail2ban: fail2ban is a daemon to ban hosts that cause multiple authentication errors

CVE-2021-32749 is fixed in fail2ban on 1 platform, first by fail2ban 0.10.2-2ubuntu0.1~esm1, released July 16, 2021. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-32749
- Priority: Routine
- CVSS: n/a (Medium)
- EPSS: 0.0343
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 16, 2021

## Description

fail2ban is a daemon to ban hosts that cause multiple authentication errors. In versions 0.9.7 and prior, 0.10.0 through 0.10.6, and 0.11.0 through 0.11.2, there is a vulnerability that leads to possible remote code execution in the mailing action mail-whois. Command `mail` from mailutils package used in mail actions like `mail-whois` can execute command if unescaped sequences (`\n~`) are available in "foreign" input (for instance in whois output). To exploit the vulnerability, an attacker would need to insert malicious characters into the response sent by the whois server, either via a MITM attack or by taking over a whois server. The issue is patched in versions 0.10.7 and 0.11.3. As a workaround, one may avoid the usage of action `mail-whois` or patch the vulnerability manually.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | fail2ban Ubuntu 18.04.6 LTS (bionic) | 0.10.2-2ubuntu0.1~esm1 | [fail2ban 0.10.2-2ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-fail2ban-0.10.2-2ubuntu0.1-esm1.md) | Jul 16, 2021 |
| Linux | fail2ban Ubuntu 20.04 LTS (focal) | 0.11.1-1ubuntu0.1~esm1 | [fail2ban 0.11.1-1ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-fail2ban-0.11.1-1ubuntu0.1-esm1.md) | Jul 16, 2021 |

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Data as of 2026-11-08T19:12:23Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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