{"id":"UBUNTU-CVE-2021-26720","details":"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.","modified":"2026-05-20T16:04:51.158076666Z","published":"2021-02-17T22:15:00Z","upstream":["CVE-2021-26720"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2021-26720"},{"type":"REPORT","url":"https://www.openwall.com/lists/oss-security/2021/02/15/2"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2021-26720"}],"affected":[{"package":{"name":"avahi","ecosystem":"Ubuntu:Pro:14.04:LTS","purl":"pkg:deb/ubuntu/avahi?arch=source&distro=esm-infra-legacy%2Ftrusty"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.6.31-2ubuntu4","0.6.31-2ubuntu5","0.6.31-3ubuntu1","0.6.31-4ubuntu1","0.6.31-4ubuntu1.1","0.6.31-4ubuntu1.2","0.6.31-4ubuntu1.3","0.6.31-4ubuntu1.3+esm1","0.6.31-4ubuntu1.3+esm2","0.6.31-4ubuntu1.3+esm3","0.6.31-4ubuntu1.3+esm4","0.6.31-4ubuntu1.3+esm5"],"ecosystem_specific":{"binaries":[{"binary_name":"avahi-autoipd","binary_version":"0.6.31-4ubuntu1.3+esm5"},{"binary_name":"avahi-daemon","binary_version":"0.6.31-4ubuntu1.3+esm5"},{"binary_name":"avahi-discover","binary_version":"0.6.31-4ubuntu1.3+esm5"},{"binary_version":"0.6.31-4ubuntu1.3+esm5","binary_name":"avahi-dnsconfd"},{"binary_name":"avahi-ui-utils","binary_version":"0.6.31-4ubuntu1.3+esm5"},{"binary_name":"avahi-utils","binary_version":"0.6.31-4ubuntu1.3+esm5"},{"binary_name":"libavahi-client3","binary_version":"0.6.31-4ubuntu1.3+esm5"},{"binary_name":"libavahi-common-data","binary_version":"0.6.31-4ubuntu1.3+esm5"},{"binary_name":"libavahi-common3","binary_version":"0.6.31-4ubuntu1.3+esm5"},{"binary_version":"0.6.31-4ubuntu1.3+esm5","binary_name":"libavahi-compat-libdnssd1"},{"binary_name":"libavahi-core7","binary_version":"0.6.31-4ubuntu1.3+esm5"},{"binary_name":"libavahi-glib1","binary_version":"0.6.31-4ubuntu1.3+esm5"},{"binary_name":"libavahi-gobject0","binary_version":"0.6.31-4ubuntu1.3+esm5"},{"binary_version":"0.6.31-4ubuntu1.3+esm5","binary_name":"libavahi-qt4-1"},{"binary_name":"libavahi-ui-gtk3-0","binary_version":"0.6.31-4ubuntu1.3+esm5"},{"binary_name":"libavahi-ui0","binary_version":"0.6.31-4ubuntu1.3+esm5"},{"binary_name":"python-avahi","binary_version":"0.6.31-4ubuntu1.3+esm5"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-26720.json"}},{"package":{"name":"avahi","ecosystem":"Ubuntu:Pro:16.04:LTS","purl":"pkg:deb/ubuntu/avahi?arch=source&distro=esm-infra-legacy%2Fxenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.6.31-4ubuntu4","0.6.32~rc+dfsg-1ubuntu2","0.6.32~rc+dfsg-1ubuntu2.1","0.6.32~rc+dfsg-1ubuntu2.2","0.6.32~rc+dfsg-1ubuntu2.3","0.6.32~rc+dfsg-1ubuntu2.3+esm1","0.6.32~rc+dfsg-1ubuntu2.3+esm2","0.6.32~rc+dfsg-1ubuntu2.3+esm3","0.6.32~rc+dfsg-1ubuntu2.3+esm4","0.6.32~rc+dfsg-1ubuntu2.3+esm5"],"ecosystem_specific":{"binaries":[{"binary_name":"avahi-autoipd","binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5"},{"binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5","binary_name":"avahi-daemon"},{"binary_name":"avahi-discover","binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5"},{"binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5","binary_name":"avahi-dnsconfd"},{"binary_name":"avahi-ui-utils","binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5"},{"binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5","binary_name":"avahi-utils"},{"binary_name":"libavahi-client3","binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5"},{"binary_name":"libavahi-common-data","binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5"},{"binary_name":"libavahi-common3","binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5"},{"binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5","binary_name":"libavahi-compat-libdnssd1"},{"binary_name":"libavahi-core7","binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5"},{"binary_name":"libavahi-glib1","binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5"},{"binary_name":"libavahi-gobject0","binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5"},{"binary_name":"libavahi-qt4-1","binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5"},{"binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5","binary_name":"libavahi-ui-gtk3-0"},{"binary_name":"libavahi-ui0","binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5"},{"binary_name":"python-avahi","binary_version":"0.6.32~rc+dfsg-1ubuntu2.3+esm5"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-26720.json"}},{"package":{"name":"avahi","ecosystem":"Ubuntu:Pro:18.04:LTS","purl":"pkg:deb/ubuntu/avahi?arch=source&distro=esm-infra%2Fbionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.6.32-1ubuntu1","0.7-3ubuntu1","0.7-3ubuntu2","0.7-3.1ubuntu1","0.7-3.1ubuntu1.1","0.7-3.1ubuntu1.2","0.7-3.1ubuntu1.3","0.7-3.1ubuntu1.3+esm1","0.7-3.1ubuntu1.3+esm2","0.7-3.1ubuntu1.3+esm3","0.7-3.1ubuntu1.3+esm4"],"ecosystem_specific":{"binaries":[{"binary_version":"0.7-3.1ubuntu1.3+esm4","binary_name":"avahi-autoipd"},{"binary_name":"avahi-daemon","binary_version":"0.7-3.1ubuntu1.3+esm4"},{"binary_name":"avahi-discover","binary_version":"0.7-3.1ubuntu1.3+esm4"},{"binary_name":"avahi-dnsconfd","binary_version":"0.7-3.1ubuntu1.3+esm4"},{"binary_name":"avahi-ui-utils","binary_version":"0.7-3.1ubuntu1.3+esm4"},{"binary_version":"0.7-3.1ubuntu1.3+esm4","binary_name":"avahi-utils"},{"binary_version":"0.7-3.1ubuntu1.3+esm4","binary_name":"gir1.2-avahi-0.6"},{"binary_name":"libavahi-client3","binary_version":"0.7-3.1ubuntu1.3+esm4"},{"binary_version":"0.7-3.1ubuntu1.3+esm4","binary_name":"libavahi-common-data"},{"binary_version":"0.7-3.1ubuntu1.3+esm4","binary_name":"libavahi-common3"},{"binary_name":"libavahi-compat-libdnssd1","binary_version":"0.7-3.1ubuntu1.3+esm4"},{"binary_version":"0.7-3.1ubuntu1.3+esm4","binary_name":"libavahi-core7"},{"binary_name":"libavahi-glib1","binary_version":"0.7-3.1ubuntu1.3+esm4"},{"binary_version":"0.7-3.1ubuntu1.3+esm4","binary_name":"libavahi-gobject0"},{"binary_name":"libavahi-ui-gtk3-0","binary_version":"0.7-3.1ubuntu1.3+esm4"},{"binary_name":"python-avahi","binary_version":"0.7-3.1ubuntu1.3+esm4"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-26720.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"},{"type":"Ubuntu","score":"low"}]}