CVE-2021-26720

Name: CVE-2021-26720
Creator: NVD / NIST
Published: 2021-02-17T22:15:12.71+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.8/10EPSS 0.40%

Last modified Jun 17, 2026

CVE-2021-26720 is a high-severity vulnerability rated 7.8/10 on the CVSS scale. avahi-daemon-check-dns.sh in the Debian avahi package through 0.8-4 is executed as root via /etc/network/if-up.d/avahi-daemon, and allows a local attacker to cause a denial of service or create arbitrary empty files via a symlink attack on files under /run/avahi-daemon. NOTE: this only affects the packaging for Debian GNU/Linux (used indirectly by SUSE), not the upstream Avahi product.. EPSS estimates a 0.40% chance of exploitation in the next 30 days.

Description

avahi-daemon-check-dns.sh in the Debian avahi package through 0.8-4 is executed as root via /etc/network/if-up.d/avahi-daemon, and allows a local attacker to cause a denial of service or create arbitrary empty files via a symlink attack on files under /run/avahi-daemon. NOTE: this only affects the packaging for Debian GNU/Linux (used indirectly by SUSE), not the upstream Avahi product.

Metrics

CVSS 3.1

7.8/10

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

EPSS Probability

0.40%

31.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-59

Affected Software

Vendor	Product	Versions
Avahi	Avahi	<= 0.8-4
Debian	Debian Linux	9.0
Debian	Debian Linux	10.0

References

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=982796Mailing List, Third Party Advisory
https://bugs.launchpad.net/ubuntu/+source/avahi/+bug/1870824Issue Tracking, Third Party Advisory
https://bugzilla.suse.com/show_bug.cgi?id=1180827Issue Tracking, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/06/msg00009.htmlMailing List, Third Party Advisory
https://metadata.ftp-master.debian.org/changelogs/main/a/avahi/avahi_0.8-4_changelogBroken Link, Third Party Advisory
https://packages.debian.org/bullseye/avahi-daemonProduct, Third Party Advisory
https://packages.debian.org/buster/avahi-daemonProduct, Third Party Advisory
https://packages.debian.org/sid/avahi-daemonProduct, Third Party Advisory
https://security-tracker.debian.org/tracker/CVE-2021-26720Third Party Advisory
https://www.openwall.com/lists/oss-security/2021/02/15/2Mailing List, Third Party Advisory
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=982796Mailing List, Third Party Advisory
https://bugs.launchpad.net/ubuntu/+source/avahi/+bug/1870824Issue Tracking, Third Party Advisory
https://bugzilla.suse.com/show_bug.cgi?id=1180827Issue Tracking, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/06/msg00009.htmlMailing List, Third Party Advisory
https://metadata.ftp-master.debian.org/changelogs/main/a/avahi/avahi_0.8-4_changelogBroken Link, Third Party Advisory
https://packages.debian.org/bullseye/avahi-daemonProduct, Third Party Advisory
https://packages.debian.org/buster/avahi-daemonProduct, Third Party Advisory
https://packages.debian.org/sid/avahi-daemonProduct, Third Party Advisory
https://security-tracker.debian.org/tracker/CVE-2021-26720Third Party Advisory
https://www.openwall.com/lists/oss-security/2021/02/15/2Mailing List, Third Party Advisory

Timeline

Published: Feb 17, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-26720?

How severe is CVE-2021-26720?

CVE-2021-26720 has a CVSS score of 7.8/10 (HIGH severity). The EPSS model estimates a 0.40% probability of exploitation in the next 30 days.

How do I fix CVE-2021-26720?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-26720?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST