What is CVE-2021-26720?

CVE-2021-26720 is a high-severity vulnerability in Avahi, classified under Improper Link Resolution Before File Access. CVSS score: 7.8/10. Published 2021-02-17.

How severe is CVE-2021-26720?

High severity. CVSS v3 base score is 7.8 out of 10.

Vulnerability in Avahi

CVE-2021-26720

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.

Published 2021-02-17 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.8 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.004 (31.1th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 31st percentile — 31.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000

Affected products

Avahi
Debian Linux — versions 9.0, 10.0

Weakness classification (CWE)

CWE-59 — Improper Link Resolution Before File Access

References

packages.debian.org/buster/avahi-daemon (Product, Third Party Advisory)
packages.debian.org/sid/avahi-daemon (Product, Third Party Advisory)
packages.debian.org/bullseye/avahi-daemon (Product, Third Party Advisory)
security-tracker.debian.org/tracker/CVE-2021-26720 (Third Party Advisory)
bugs.launchpad.net/ubuntu/+source/avahi/+bug/1870824 (Third Party Advisory, Issue Tracking)
metadata.ftp-master.debian.org/changelogs/main/a/avahi/avahi_0.8-4_changelog (Third Party Advisory, Broken Link)
www.openwall.com/lists/oss-security/2021/02/15/2 (Mailing List, Third Party Advisory)
bugs.debian.org/cgi-bin/bugreport.cgi (Mailing List, Third Party Advisory)
bugzilla.suse.com/show_bug.cgi (Third Party Advisory, Issue Tracking)
lists.debian.org/debian-lts-announce/2022/06/msg00009.html (mailing-list, Mailing List, Third Party Advisory)

Frequently asked questions

What is CVE-2021-26720?: CVE-2021-26720 is a high-severity vulnerability in Avahi, classified under Improper Link Resolution Before File Access. CVSS score: 7.8/10. Published 2021-02-17.
How severe is CVE-2021-26720?: High severity. CVSS v3 base score is 7.8 out of 10.