CVE-2021-3468 [Medium] | Security Vulnerability in Avahi

A flaw was found in avahi in versions 0.6 up to 0.8. The event used to signal the termination of the client connection on the avahi Unix socket is not correctly handled in the client_work function, allowing a local attacker to trigger an infinite loop. The highest threat from this vulnerability is to the availability of the avahi service, which becomes unresponsive after this flaw is triggered.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.04%	0.45%	+0.41%
2	2023-03-07	0.89%	0.04%	-0.84%
3	2022-04-01	—	0.89%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

0.04%

0.45%

+0.41%

2023-03-07

0.89%

0.04%

-0.84%

2022-04-01

—

0.89%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
5.5	3.1	MEDIUM	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H` Click to expand Attack vector (AV:L) They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:L) A normal user session is enough; they don’t have to be admin. 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:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	1.8	3.6	[email protected]
2.1	2.0	LOW	`AV:L/AC:L/Au:N/C:N/I:N/A:P` Click to expand Access vector (AV:L) Requires local access to the target system. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. Authentication (AU:N) No authentication is required. Confidentiality impact (C:N) No confidentiality impact. Integrity impact (I:N) No integrity impact. Availability impact (A:P) Partial availability impact.	3.9	2.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

5.5

3.1

MEDIUM

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

Attack vector (AV:L): They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L): A normal user session is enough; they don’t have to be admin.
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:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

1.8

3.6

[email protected]

2.1

2.0

LOW

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

Access vector (AV:L): Requires local access to the target system.
Access complexity (AC:L): Exploitation conditions are straightforward and predictable.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:N): No confidentiality impact.
Integrity impact (I:N): No integrity impact.
Availability impact (A:P): Partial availability impact.

3.9

2.9

[email protected]

OS Trackers for CVE-2021-3468

vendor	priority	summary	link
`alpine`	medium	CVE-2021-3468: 1 source package rows (avahi); 65 state rows across 11 repos (3.10-main, 3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, 3.23-main, edge-main); fixed 55, open 10.	https://security.alpinelinux.org/vuln/CVE-2021-3468
`debian`	not yet assigned	CVE-2021-3468 not yet assigned priority: Debian including 1 source packages (avahi), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2021-3468
`redhat`	medium	—	https://access.redhat.com/security/cve/CVE-2021-3468
`suse`	medium	CVE-2021-3468 severity moderate: SUSE including 513 source package names (5.2.2-5.24:libavahi-client3-0.7-3.9.1, 5.2.2-5.24:libavahi-common3-0.7-3.9.1, …), 1167 product×package rows across 120 product lines (Container suse/pcp, Container suse/sle-micro-rancher/5.2, … (120 product lines)): Fixed 1030, Known Affected 137.	https://www.suse.com/security/cve/CVE-2021-3468/
`ubuntu`	medium	CVE-2021-3468 medium priority: Ubuntu including 1 source packages (avahi), 9 status rows across 9 suites (bionic, focal, groovy, hirsute, impish, jammy, trusty, upstream, xenial): released 8, needed 1.	https://ubuntu.com/security/CVE-2021-3468

Affected software / configurations for CVE-2021-3468

Vendor	Product	Version	Raw CPE
avahi	avahi	>= 0.6, <= 0.8	cpe:2.3:a:avahi:avahi::::::::
debian	debian_linux	9.0	cpe:2.3:o:debian:debian_linux:9.0:::::::*

References for CVE-2021-3468

URL	Tags
https://bugzilla.redhat.com/show_bug.cgi?id=1939614	Issue Tracking
https://lists.debian.org/debian-lts-announce/2022/06/msg00009.html	Mailing List Third Party Advisory
https://lists.debian.org/debian-lts-announce/2023/06/msg00028.html

URL

CVE-2021-3468

Exploit prediction scoring system (EPSS) score for CVE-2021-3468

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3468

Weakness enumeration for CVE-2021-3468

OS Trackers for CVE-2021-3468

Affected software / configurations for CVE-2021-3468

References for CVE-2021-3468