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

This month

MEDIUM 6.1UPGRADEMITIGATE

CVE-2021-32749 is a medium-severity flaw (CVSS 6.1) affecting fail2ban, fedora. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	Required
EPSS exploit chance	3.4% (top 11%)
CISA exploited list	No
Weakness	CWE-78, CWE-94
Published	2021-07-16
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: fail2ban · fedoraproject

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-07-16 18:15 UTCPublished CVE record published
2026-06-17 03:53 UTCUpdated Record last modified

fail2ban fail2ban UPGRADE

Affected: <= 0.9.7 · >= 0.10.0 and < 0.10.7 · >= 0.11.0 and < 0.11.3

Fixed in: 0.10.7, 0.11.3

Safe to downgrade to: a release before 0.10.0

1. Check installed version

apt-cache policy fail2ban || rpm -q fail2ban || fail2ban --version

2. UPGRADE to 0.10.7 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade fail2ban

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade fail2ban

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 0.10.0 (Debian / Ubuntu)

apt-cache madison fail2ban sudo apt install fail2ban=<VERSION_BEFORE_0.10.0> sudo apt-mark hold fail2ban

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list fail2ban sudo dnf downgrade fail2ban-<VERSION_BEFORE_0.10.0> sudo dnf versionlock add fail2ban

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

fedoraproject fedora MITIGATE

Affected: 34 · 35

Fixed in: no fixed release known

Safe to downgrade to: a release before 34

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-32749?

fail2ban: upgrade to 0.10.7, 0.11.3; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-32749 being exploited?

CVE-2021-32749 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-32749 affect?

CVE-2021-32749 affects fail2ban, fedora. Severity is medium (CVSS 6.1). 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

How urgent is CVE-2021-32749?

Priority 49/100. Public exploit reference

Related CVEs

CVE-2013-7177 MEDIUM 5.0 UPGRADE config/filter.d/cyrus-imap.conf in the cyrus-imap filter in Fail2ban before 0.8.11 allows remote attackers to
CVE-2013-7176 MEDIUM 5.0 UPGRADE config/filter.d/postfix.conf in the postfix filter in Fail2ban before 0.8.11 allows remote attackers to trigge
CVE-2013-2178 MEDIUM 5.0 UPGRADE The apache-auth.conf, apache-nohome.conf, apache-noscript.conf, and apache-overflows.conf files in Fail2ban be
CVE-2012-5642 HIGH 7.5 UPGRADE server/action.py in Fail2ban before 0.8.8 does not properly handle the content of the matches tag, which might
CVE-2009-5023 MEDIUM 4.7 UPGRADE The (1) dshield.conf, (2) mail-buffered.conf, (3) mynetwatchman.conf, and (4) mynetwatchman.conf actions in ac

References

← Back to latest CVEs