CVE-2021-26720 Path traversal in n/a
Local attackers can cause denial of service or create arbitrary files via symlink attacks in the Debian Avahi package script.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-26720?
CVE-2021-26720 is a high-severity path traversal vulnerability in Debian Debian Linux, published on 17 Feb 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-59
Which versions are affected by CVE-2021-26720?
It affects 2 products.
Linux distribution packages (16)
avahi SUSE:Linux Enterprise Module for Basesystem 15 SP2 | All versions | 0.7-3.6.1 |
avahi-glib2 SUSE:Linux Enterprise Module for Basesystem 15 SP2 | All versions | 0.7-3.6.1 |
avahi SUSE:Linux Enterprise Module for Desktop Applications 15 SP2 | All versions | 0.7-3.6.1 |
avahi-glib2 SUSE:Linux Enterprise Module for Desktop Applications 15 SP2 | All versions | 0.7-3.6.1 |
avahi SUSE:Linux Enterprise Module for Package Hub 15 SP2 | All versions | 0.7-3.6.1 |
avahi SUSE:Linux Enterprise Server 12 SP5 | All versions | 0.6.32-32.12.2 |
avahi-glib2 SUSE:Linux Enterprise Server 12 SP5 | All versions | 0.6.32-32.12.3 |
avahi SUSE:Linux Enterprise Server for SAP Applications 12 SP5 | All versions | 0.6.32-32.12.2 |
avahi-glib2 SUSE:Linux Enterprise Server for SAP Applications 12 SP5 | All versions | 0.6.32-32.12.3 |
avahi SUSE:Linux Enterprise Software Development Kit 12 SP5 | All versions | 0.6.32-32.12.2 |
avahi-glib2 SUSE:Linux Enterprise Software Development Kit 12 SP5 | All versions | 0.6.32-32.12.3 |
avahi-glib2 SUSE:Linux Enterprise Workstation Extension 12 SP5 | All versions | 0.6.32-32.12.3 |
avahi openSUSE:Leap 15.2 | All versions | 0.7-lp152.3.6.1 |
avahi-glib2 openSUSE:Leap 15.2 | All versions | 0.7-lp152.3.6.1 |
avahi-mono openSUSE:Leap 15.2 | All versions | 0.7-lp152.3.6.1 |
avahi-qt4 openSUSE:Leap 15.2 | All versions | 0.7-lp152.3.6.1 |
Products include Avahi Avahi, Debian Debian Linux.
How do I fix CVE-2021-26720?
Apply the vendor's patch.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2021-26720 being exploited?
There is no known exploitation of CVE-2021-26720 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
- CVE-2017-6519 Denial of service in n/a
- CVE-2026-24401 Avahi has Uncontrolled Recursion in lookup_handle_cname function
- CVE-2025-68468 Avahi has a reachable assertion in lookup_multicast_callback
- CVE-2025-68471 Avahi has a reachable assertion in lookup_start
- CVE-2023-38469 Reachable assertion in avahi_dns_packet_append_record
Sources
Also known as AZL-34547, AZL-6323, CLSA-2026-1787932412, DEBIAN-CVE-2021-26720, GHSA-jhxr-wvf5-hrp6, SUSE-SU-2021:0551-1 and 3 more.