{"id":"UBUNTU-CVE-2021-21261","details":"Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux. A bug was discovered in the `flatpak-portal` service that can allow sandboxed applications to execute arbitrary code on the host system (a sandbox escape). This sandbox-escape bug is present in versions from 0.11.4 and before fixed versions 1.8.5 and 1.10.0. The Flatpak portal D-Bus service (`flatpak-portal`, also known by its D-Bus service name `org.freedesktop.portal.Flatpak`) allows apps in a Flatpak sandbox to launch their own subprocesses in a new sandbox instance, either with the same security settings as the caller or with more restrictive security settings. For example, this is used in Flatpak-packaged web browsers such as Chromium to launch subprocesses that will process untrusted web content, and give those subprocesses a more restrictive sandbox than the browser itself. In vulnerable versions, the Flatpak portal service passes caller-specified environment variables to non-sandboxed processes on the host system, and in particular to the `flatpak run` command that is used to launch the new sandbox instance. A malicious or compromised Flatpak app could set environment variables that are trusted by the `flatpak run` command, and use them to execute arbitrary code that is not in a sandbox. As a workaround, this vulnerability can be mitigated by preventing the `flatpak-portal` service from starting, but that mitigation will prevent many Flatpak apps from working correctly. This is fixed in versions 1.8.5 and 1.10.0.","modified":"2026-04-22T14:30:42.925797Z","published":"2021-01-14T20:15:00Z","related":["USN-4721-1"],"upstream":["CVE-2021-21261"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2021-21261"},{"type":"REPORT","url":"https://github.com/flatpak/flatpak/security/advisories/GHSA-4ppf-fxf6-vxg2"},{"type":"ADVISORY","url":"https://ubuntu.com/security/notices/USN-4721-1"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2021-21261"}],"affected":[{"package":{"name":"flatpak","ecosystem":"Ubuntu:18.04:LTS","purl":"pkg:deb/ubuntu/flatpak@1.0.9-0ubuntu0.2?arch=source&distro=bionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.0.9-0ubuntu0.2"}]}],"versions":["0.8.7-5","0.10.0-1","0.10.0-2","0.10.1-1","0.10.2-1","0.10.2.1-1","0.10.2.1-2","0.10.3-1","0.11.1-0ubuntu1","0.11.3-2","0.11.3-3","0.11.7-0ubuntu0.1","1.0.1-0ubuntu0.1","1.0.6-0ubuntu0.1","1.0.7-0ubuntu0.18.04.1","1.0.8-0ubuntu0.18.04.1","1.0.9-0ubuntu0.1"],"ecosystem_specific":{"availability":"No subscription required","binaries":[{"binary_name":"flatpak","binary_version":"1.0.9-0ubuntu0.2"},{"binary_name":"flatpak-tests","binary_version":"1.0.9-0ubuntu0.2"},{"binary_name":"gir1.2-flatpak-1.0","binary_version":"1.0.9-0ubuntu0.2"},{"binary_name":"libflatpak0","binary_version":"1.0.9-0ubuntu0.2"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-21261.json"}},{"package":{"name":"flatpak","ecosystem":"Ubuntu:20.04:LTS","purl":"pkg:deb/ubuntu/flatpak@1.6.5-0ubuntu0.2?arch=source&distro=focal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.6.5-0ubuntu0.2"}]}],"versions":["1.4.3-1","1.6.0-1","1.6.1-1","1.6.2-1","1.6.3-1","1.6.5-0ubuntu0.1"],"ecosystem_specific":{"availability":"No subscription required","binaries":[{"binary_name":"flatpak","binary_version":"1.6.5-0ubuntu0.2"},{"binary_version":"1.6.5-0ubuntu0.2","binary_name":"flatpak-tests"},{"binary_version":"1.6.5-0ubuntu0.2","binary_name":"gir1.2-flatpak-1.0"},{"binary_name":"libflatpak0","binary_version":"1.6.5-0ubuntu0.2"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-21261.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H"},{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N"},{"type":"Ubuntu","score":"medium"}]}