{"id":"UBUNTU-CVE-2021-21284","details":"In Docker before versions 9.03.15, 20.10.3 there is a vulnerability involving the --userns-remap option in which access to remapped root allows privilege escalation to real root. When using \"--userns-remap\", if the root user in the remapped namespace has access to the host filesystem they can modify files under \"/var/lib/docker/\u003cremapping\u003e\" that cause writing files with extended privileges. Versions 20.10.3 and 19.03.15 contain patches that prevent privilege escalation from remapped user.","modified":"2026-01-30T01:49:35.438341Z","published":"2021-02-02T18:15:00Z","related":["USN-5032-1","USN-5032-2"],"upstream":["CVE-2021-21284"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2021-21284"},{"type":"REPORT","url":"https://github.com/moby/moby/security/advisories/GHSA-7452-xqpj-6rpc"},{"type":"REPORT","url":"https://docs.docker.com/engine/release-notes/#20103"},{"type":"REPORT","url":"https://github.com/moby/moby/commit/64bd4485b3a66a597c02c95f5776395e540b2c7c"},{"type":"REPORT","url":"https://github.com/moby/moby/releases/tag/v19.03.15"},{"type":"REPORT","url":"https://github.com/moby/moby/releases/tag/v20.10.3"},{"type":"ADVISORY","url":"https://ubuntu.com/security/notices/USN-5032-1"},{"type":"ADVISORY","url":"https://ubuntu.com/security/notices/USN-5032-2"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2021-21284"}],"affected":[{"package":{"name":"docker.io","ecosystem":"Ubuntu:Pro:16.04:LTS","purl":"pkg:deb/ubuntu/docker.io@18.09.7-0ubuntu1~16.04.9+esm2?arch=source&distro=esm-infra/xenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.6.2~dfsg1-1ubuntu4","1.10.2-0ubuntu3","1.10.2-0ubuntu4","1.10.3-0ubuntu1","1.10.3-0ubuntu4","1.10.3-0ubuntu5","1.10.3-0ubuntu6","1.11.2-0ubuntu5~16.04","1.12.1-0ubuntu13~16.04.1","1.12.3-0ubuntu4~16.04.2","1.12.6-0ubuntu1~16.04.1","1.13.1-0ubuntu1~16.04.2","17.03.2-0ubuntu2~16.04.1","18.06.1-0ubuntu1~16.04.2","18.06.1-0ubuntu1.2~16.04.1","18.09.2-0ubuntu1~16.04.1","18.09.5-0ubuntu1~16.04.2","18.09.7-0ubuntu1~16.04.1","18.09.7-0ubuntu1~16.04.4","18.09.7-0ubuntu1~16.04.5","18.09.7-0ubuntu1~16.04.6","18.09.7-0ubuntu1~16.04.7","18.09.7-0ubuntu1~16.04.9+esm1","18.09.7-0ubuntu1~16.04.9+esm2"],"ecosystem_specific":{"binaries":[{"binary_name":"docker.io","binary_version":"18.09.7-0ubuntu1~16.04.9+esm2"},{"binary_name":"golang-docker-dev","binary_version":"18.09.7-0ubuntu1~16.04.9+esm2"},{"binary_name":"golang-github-docker-docker-dev","binary_version":"18.09.7-0ubuntu1~16.04.9+esm2"},{"binary_name":"vim-syntax-docker","binary_version":"18.09.7-0ubuntu1~16.04.9+esm2"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-21284.json"}},{"package":{"name":"docker.io","ecosystem":"Ubuntu:18.04:LTS","purl":"pkg:deb/ubuntu/docker.io@20.10.7-0ubuntu1~18.04.1?arch=source&distro=bionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"20.10.7-0ubuntu1~18.04.1"}]}],"versions":["1.13.1-0ubuntu6","17.03.2-0ubuntu1","17.03.2-0ubuntu3","17.03.2-0ubuntu5","17.12.1-0ubuntu1","18.06.1-0ubuntu1~18.04.1","18.06.1-0ubuntu1.2~18.04.1","18.09.2-0ubuntu1~18.04.1","18.09.5-0ubuntu1~18.04.2","18.09.7-0ubuntu1~18.04.1","18.09.7-0ubuntu1~18.04.3","18.09.7-0ubuntu1~18.04.4","19.03.6-0ubuntu1~18.04.1","19.03.6-0ubuntu1~18.04.2","19.03.6-0ubuntu1~18.04.3","20.10.2-0ubuntu1~18.04.2","20.10.2-0ubuntu1~18.04.3"],"ecosystem_specific":{"availability":"No subscription required","binaries":[{"binary_version":"20.10.7-0ubuntu1~18.04.1","binary_name":"docker.io"},{"binary_name":"golang-docker-dev","binary_version":"20.10.7-0ubuntu1~18.04.1"},{"binary_version":"20.10.7-0ubuntu1~18.04.1","binary_name":"golang-github-docker-docker-dev"},{"binary_name":"vim-syntax-docker","binary_version":"20.10.7-0ubuntu1~18.04.1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-21284.json"}},{"package":{"name":"docker.io","ecosystem":"Ubuntu:20.04:LTS","purl":"pkg:deb/ubuntu/docker.io@20.10.7-0ubuntu1~20.04.1?arch=source&distro=focal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"20.10.7-0ubuntu1~20.04.1"}]}],"versions":["19.03.2-0ubuntu1","19.03.6-0ubuntu1","19.03.8-0ubuntu1","19.03.8-0ubuntu1.20.04","19.03.8-0ubuntu1.20.04.1","19.03.8-0ubuntu1.20.04.2","20.10.2-0ubuntu1~20.04.2","20.10.2-0ubuntu1~20.04.3"],"ecosystem_specific":{"availability":"No subscription required","binaries":[{"binary_name":"docker.io","binary_version":"20.10.7-0ubuntu1~20.04.1"},{"binary_name":"golang-docker-dev","binary_version":"20.10.7-0ubuntu1~20.04.1"},{"binary_name":"golang-github-docker-docker-dev","binary_version":"20.10.7-0ubuntu1~20.04.1"},{"binary_version":"20.10.7-0ubuntu1~20.04.1","binary_name":"vim-syntax-docker"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-21284.json"}}],"schema_version":"1.7.3","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N"},{"type":"CVSS_V3","score":"CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N"},{"type":"Ubuntu","score":"medium"}]}