CVE-2021-32749 [Medium] | Command Injection in Fail2ban

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.

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#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2025-11-21	1.96%	0.30%	-1.66%
2	2025-11-18	0.30%	1.96%	+1.66%
3	2025-10-20	—	0.30%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2025-11-21

1.96%

0.30%

-1.66%

2025-11-18

0.30%

1.96%

+1.66%

2025-10-20

—

0.30%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
6.1	3.1	MEDIUM	`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:N` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:H) Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:R) A real person has to do something—click, install, enable—otherwise it doesn’t land. Scope (S:C) Breaking this can reach past the original component and bite other resources—bigger blast radius. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:N) Service keeps running; no real outage angle.	1.6	4.0	[email protected]
8.1	3.1	HIGH	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:H) Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	2.2	5.9	[email protected]
6.8	2.0	MEDIUM	`AV:N/AC:M/Au:N/C:P/I:P/A:P` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:M) Exploitation needs some favorable conditions, but not exceptional ones. Authentication (AU:N) No authentication is required. Confidentiality impact (C:P) Partial confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:P) Partial availability impact.	8.6	6.4	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

6.1

3.1

MEDIUM

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:N Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H): Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R): A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:C): Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N): Service keeps running; no real outage angle.

1.6

4.0

[email protected]

8.1

3.1

HIGH

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H): Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

2.2

5.9

[email protected]

6.8

2.0

MEDIUM

AV:N/AC:M/Au:N/C:P/I:P/A:P Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:M): Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:P): Partial confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:P): Partial availability impact.

8.6

6.4

[email protected]

OS Trackers for CVE-2021-32749

vendor	priority	summary	link
`alpine`	high	CVE-2021-32749: 1 source package rows (fail2ban); 10 state rows across 9 repos (3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 8, open 2.	https://security.alpinelinux.org/vuln/CVE-2021-32749
`debian`	not yet assigned	CVE-2021-32749 not yet assigned priority: Debian including 1 source packages (fail2ban), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2021-32749
`gentoo`	high	CVE-2021-32749: 1 GLSA(s) (202310-13), 1 atom(s) (net-mail/mailutils); latest impact high.	https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-32749
`ubuntu`	medium	CVE-2021-32749 medium priority: Ubuntu including 1 source packages (fail2ban), 15 status rows across 15 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, trusty, upstream, xenial): not-affected 8, released 5, ignored 2.	https://ubuntu.com/security/CVE-2021-32749

Affected software / configurations for CVE-2021-32749

Vendor	Product	Version	Raw CPE
fail2ban	fail2ban	<= 0.9.7	cpe:2.3:a:fail2ban:fail2ban::::::::
fail2ban	fail2ban	>= 0.10.0, < 0.10.7	cpe:2.3:a:fail2ban:fail2ban::::::::
fail2ban	fail2ban	>= 0.11.0, < 0.11.3	cpe:2.3:a:fail2ban:fail2ban::::::::
fedoraproject	fedora	34	cpe:2.3:o:fedoraproject:fedora:34:::::::*
fedoraproject	fedora	35	cpe:2.3:o:fedoraproject:fedora:35:::::::*

References for CVE-2021-32749

URL	Tags
https://github.com/fail2ban/fail2ban/commit/2ed414ed09b3bb4c478abc9366a1ff22024a33c9	Patch Third Party Advisory
https://github.com/fail2ban/fail2ban/commit/410a6ce5c80dd981c22752da034f2529b5eee844	Patch Third Party Advisory
https://github.com/fail2ban/fail2ban/security/advisories/GHSA-m985-3f3v-cwmm	Exploit Patch Third Party Advisory
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

URL

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

Public exploit references (Exploit-DB) for CVE-2021-32749

Exploit prediction scoring system (EPSS) score for CVE-2021-32749

Common vulnerability scoring system (CVSS) metrics for CVE-2021-32749

Weakness enumeration for CVE-2021-32749

OS Trackers for CVE-2021-32749

Affected software / configurations for CVE-2021-32749

References for CVE-2021-32749