{ "document": { "aggregate_severity": { "text": "Important" }, "category": "csaf_security_advisory", "csaf_version": "2.0", "distribution": { "text": "TuxCare License Agreement", "tlp": { "label": "WHITE", "url": "https://www.first.org/tlp/" } }, "lang": "en", "notes": [ { "category": "legal_disclaimer", "text": "This content is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). If you distribute this content, or a modified version of it, you must provide attribution to Cloud Linux Inc. and provide a link to the original.", "title": "Terms of Use" }, { "category": "details", "text": "* SECURITY UPDATE: local symlink attack through the unicast .local DNS\n check: /etc/network/if-up.d/avahi-daemon exec's\n /usr/lib/avahi/avahi-daemon-check-dns.sh as root, and the script\n writes into /run/avahi-daemon (the checked_nameservers[.$$] cache and\n the disabled-for-unicast-local tag) without protecting against\n symlinks, so a local attacker able to place symlinks in that\n avahi-owned directory can make root create arbitrary empty files or\n cause a denial of service.\n - debian/avahi-daemon.if-up: run the check script under\n \"sudo -u avahi -g avahi\" instead of exec'ing it as root, so the\n writes are performed by the same unprivileged account that owns\n /run/avahi-daemon. Backported verbatim from Debian stretch\n 0.6.32-2+deb9u1 (DLA-3047-1); the alternative vendor fix, dropping\n the check-dns mechanism outright (Debian buster 0.7-4+deb10u1,\n Ubuntu focal 0.7-4ubuntu7), is not applicable here because bionic\n ships libnss-mdns 0.10-8ubuntu1, the same generation as stretch.\n - debian/control: add sudo to the avahi-daemon Depends, required by\n the privilege drop.\n - CVE-2021-26720", "title": "Details" } ], "publisher": { "category": "vendor", "contact_details": "https://tuxcare.com/contact/", "name": "TuxCare", "namespace": "https://tuxcare.com/" }, "references": [ { "category": "self", "summary": "https://cve.tuxcare.com/els/releases/CLSA-2026:1787932412", "url": "https://cve.tuxcare.com/els/releases/CLSA-2026:1787932412" }, { "category": "self", "summary": "Canonical URL", "url": "https://security.tuxcare.com/csaf/v2/els_os/ubuntu18.04els/advisories/2026/clsa-2026_1787932412.json" } ], "tracking": { "current_release_date": "2026-08-28T15:54:41Z", "generator": { "date": "2026-08-28T15:54:41Z", "engine": { "name": "pyCSAF" } }, "id": "CLSA-2026:1787932412", "initial_release_date": "2026-08-28T15:54:41Z", "revision_history": [ { "date": "2026-08-28T15:54:41Z", "number": "1", "summary": "Initial version" } ], "status": "final", "version": "1" }, "title": "Fix CVE(s): CVE-2021-26720" }, "product_tree": { "branches": [ { "branches": [ { "branches": [ { "category": "product_name", "name": "Ubuntu 18.04", "product": { "name": "Ubuntu 18.04", "product_id": "Ubuntu-18", "product_identification_helper": { "cpe": "cpe:2.3:o:canonical:ubuntu_linux:18.04:*:*:*:lts:*:*:*" } } } ], "category": "product_family", "name": "Ubuntu" } ], "category": "vendor", "name": "Canonical Ltd." }, { "branches": [ { "branches": [ { "category": "product_version", "name": "python-avahi-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "product": { "name": "python-avahi-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "product_id": 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"relates_to_product_reference": "Ubuntu-18" }, { "category": "default_component_of", "full_product_name": { "name": "libavahi-compat-libdnssd1-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64 as a component of Ubuntu 18.04", "product_id": "Ubuntu-18:libavahi-compat-libdnssd1-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64" }, "product_reference": "libavahi-compat-libdnssd1-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "relates_to_product_reference": "Ubuntu-18" }, { "category": "default_component_of", "full_product_name": { "name": "libavahi-gobject0-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64 as a component of Ubuntu 18.04", "product_id": "Ubuntu-18:libavahi-gobject0-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64" }, "product_reference": "libavahi-gobject0-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "relates_to_product_reference": "Ubuntu-18" }, { "category": "default_component_of", "full_product_name": { "name": "libavahi-common-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64 as a component of Ubuntu 18.04", "product_id": "Ubuntu-18:libavahi-common-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64" }, "product_reference": "libavahi-common-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "relates_to_product_reference": "Ubuntu-18" }, { "category": "default_component_of", "full_product_name": { "name": "libavahi-ui-gtk3-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64 as a component of Ubuntu 18.04", "product_id": "Ubuntu-18:libavahi-ui-gtk3-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64" }, "product_reference": "libavahi-ui-gtk3-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "relates_to_product_reference": "Ubuntu-18" }, { "category": "default_component_of", "full_product_name": { "name": "avahi-daemon-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64 as a component of Ubuntu 18.04", "product_id": "Ubuntu-18:avahi-daemon-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64" }, "product_reference": "avahi-daemon-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "relates_to_product_reference": "Ubuntu-18" }, { "category": "default_component_of", "full_product_name": { "name": "libavahi-ui-gtk3-0-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64 as a component of Ubuntu 18.04", "product_id": "Ubuntu-18:libavahi-ui-gtk3-0-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64" }, "product_reference": "libavahi-ui-gtk3-0-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "relates_to_product_reference": "Ubuntu-18" }, { "category": "default_component_of", "full_product_name": { "name": "libavahi-gobject-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64 as a component of Ubuntu 18.04", "product_id": "Ubuntu-18:libavahi-gobject-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64" }, "product_reference": "libavahi-gobject-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "relates_to_product_reference": "Ubuntu-18" } ] }, "vulnerabilities": [ { "cve": "CVE-2021-26720", "cwe": { "id": "CWE-59", "name": "Improper Link Resolution Before File Access ('Link Following')" }, "notes": [ { "category": "description", "text": "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.", "title": "Vulnerability description" } ], "product_status": { "fixed": [ "Ubuntu-18:avahi-autoipd-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:avahi-daemon-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:avahi-discover-0:0.7-3.1ubuntu1.3+tuxcare.els1.all", "Ubuntu-18:avahi-dnsconfd-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:avahi-ui-utils-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:avahi-utils-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:gir1.2-avahi-0.6-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-client-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-client3-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-common-data-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-common-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-common3-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-compat-libdnssd-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-compat-libdnssd1-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-core-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-core7-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-glib-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-glib1-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-gobject-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-gobject0-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-ui-gtk3-0-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-ui-gtk3-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:python-avahi-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64" ] }, "references": [ { "category": "self", "summary": "Canonical URL", "url": "https://cve.tuxcare.com/els/cve/CVE-2021-26720" }, { "category": "external", "summary": "https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=982796", "url": "https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=982796" }, { "category": "external", "summary": "https://bugs.launchpad.net/ubuntu/+source/avahi/+bug/1870824", "url": "https://bugs.launchpad.net/ubuntu/+source/avahi/+bug/1870824" }, { "category": "external", "summary": "https://bugzilla.suse.com/show_bug.cgi?id=1180827", "url": "https://bugzilla.suse.com/show_bug.cgi?id=1180827" }, { "category": "external", "summary": "https://lists.debian.org/debian-lts-announce/2022/06/msg00009.html", "url": "https://lists.debian.org/debian-lts-announce/2022/06/msg00009.html" }, { "category": "external", "summary": "https://metadata.ftp-master.debian.org/changelogs/main/a/avahi/avahi_0.8-4_changelog", "url": "https://metadata.ftp-master.debian.org/changelogs/main/a/avahi/avahi_0.8-4_changelog" }, { "category": "external", "summary": "https://packages.debian.org/bullseye/avahi-daemon", "url": "https://packages.debian.org/bullseye/avahi-daemon" }, { "category": "external", "summary": "https://packages.debian.org/buster/avahi-daemon", "url": "https://packages.debian.org/buster/avahi-daemon" }, { "category": "external", "summary": "https://packages.debian.org/sid/avahi-daemon", "url": "https://packages.debian.org/sid/avahi-daemon" }, { "category": "external", "summary": "https://security-tracker.debian.org/tracker/CVE-2021-26720", "url": "https://security-tracker.debian.org/tracker/CVE-2021-26720" }, { "category": "external", "summary": "https://www.openwall.com/lists/oss-security/2021/02/15/2", "url": "https://www.openwall.com/lists/oss-security/2021/02/15/2" } ], "release_date": "2021-02-17T22:15:00Z", "remediations": [ { "category": "vendor_fix", "date": "2026-08-28T15:53:34.049752Z", "details": "Details on how to apply the fix are available at: https://cve.tuxcare.com/els/releases/CLSA-2026:1787932412", "product_ids": [ "Ubuntu-18:avahi-autoipd-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:avahi-daemon-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:avahi-discover-0:0.7-3.1ubuntu1.3+tuxcare.els1.all", "Ubuntu-18:avahi-dnsconfd-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:avahi-ui-utils-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:avahi-utils-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:gir1.2-avahi-0.6-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-client-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-client3-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-common-data-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-common-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-common3-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-compat-libdnssd-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-compat-libdnssd1-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-core-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-core7-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-glib-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-glib1-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-gobject-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-gobject0-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-ui-gtk3-0-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:libavahi-ui-gtk3-dev-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64", "Ubuntu-18:python-avahi-0:0.7-3.1ubuntu1.3+tuxcare.els1.amd64" ], "url": "https://cve.tuxcare.com/els/releases/CLSA-2026:1787932412" } ], "threats": [ { "category": "impact", "details": "Important" } ] } ] }