CVE-2021-26720

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-02-17 · updated 2026-06-17
Weakness: CWE-59

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.

Affected products

avahi: through 0.8-4
Debian Linux: 9.0, 10.0

References

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=982796
https://bugs.launchpad.net/ubuntu/+source/avahi/+bug/1870824
https://bugzilla.suse.com/show_bug.cgi?id=1180827
https://lists.debian.org/debian-lts-announce/2022/06/msg00009.html
https://metadata.ftp-master.debian.org/changelogs/main/a/avahi/avahi_0.8-4_changelog
https://packages.debian.org/bullseye/avahi-daemon
https://packages.debian.org/buster/avahi-daemon
https://packages.debian.org/sid/avahi-daemon
https://security-tracker.debian.org/tracker/CVE-2021-26720
https://www.openwall.com/lists/oss-security/2021/02/15/2
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=982796
https://bugs.launchpad.net/ubuntu/+source/avahi/+bug/1870824

Get alerted when CVE-2021-26720 or the next vulnerability affects your stack