CVE-2021-32749

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.

Bugs

• <https://bugs.launchpad.net/ubuntu/+source/fail2ban/+bug/1939870&gt;