{"id":"CVE-2020-16120","details":"Overlayfs did not properly perform permission checking when copying up files in an overlayfs and could be exploited from within a user namespace, if, for example, unprivileged user namespaces were allowed. It was possible to have a file not readable by an unprivileged user to be copied to a mountpoint controlled by the user, like a removable device. This was introduced in kernel version 4.19 by commit d1d04ef (\"ovl: stack file ops\"). This was fixed in kernel version 5.8 by commits 56230d9 (\"ovl: verify permissions in ovl_path_open()\"), 48bd024 (\"ovl: switch to mounter creds in readdir\") and 05acefb (\"ovl: check permission to open real file\"). Additionally, commits 130fdbc (\"ovl: pass correct flags for opening real directory\") and 292f902 (\"ovl: call secutiry hook in ovl_real_ioctl()\") in kernel 5.8 might also be desired or necessary. These additional commits introduced a regression in overlay mounts within user namespaces which prevented access to files with ownership outside of the user namespace. This regression was mitigated by subsequent commit b6650da (\"ovl: do not fail because of O_NOATIMEi\") in kernel 5.11.","modified":"2026-03-13T00:32:14.134661Z","published":"2021-02-10T20:15:15.150Z","related":["SUSE-SU-2020:3122-1","SUSE-SU-2020:3272-1","SUSE-SU-2020:3281-1","SUSE-SU-2020:3326-1","SUSE-SU-2020:3484-1","SUSE-SU-2020:3491-1","SUSE-SU-2020:3512-1","SUSE-SU-2020:3513-1","SUSE-SU-2020:3522-1","SUSE-SU-2020:3532-1","SUSE-SU-2020:3544-1","openSUSE-SU-2020:1906-1","openSUSE-SU-2020:2112-1","openSUSE-SU-2021:0242-1"],"references":[{"type":"ADVISORY","url":"https://ubuntu.com/USN-4576-1"},{"type":"ADVISORY","url":"https://ubuntu.com/USN-4578-1"},{"type":"ADVISORY","url":"https://www.openwall.com/lists/oss-security/2020/10/14/2"},{"type":"ADVISORY","url":"https://ubuntu.com/USN-4577-1"},{"type":"REPORT","url":"https://launchpad.net/bugs/1900141"},{"type":"FIX","url":"https://git.kernel.org/linus/05acefb4872dae89e772729efb194af754c877e8"},{"type":"FIX","url":"https://git.kernel.org/linus/48bd024b8a40d73ad6b086de2615738da0c7004f"},{"type":"FIX","url":"https://git.kernel.org/linus/b6650dab404c701d7fe08a108b746542a934da84"},{"type":"FIX","url":"https://launchpad.net/bugs/1894980"},{"type":"FIX","url":"https://git.kernel.org/linus/56230d956739b9cb1cbde439d76227d77979a04d"},{"type":"FIX","url":"https://git.kernel.org/linus/d1d04ef8572bc8c22265057bd3d5a79f223f8f52"}],"affected":[{"database_specific":{"unresolved_ranges":[{"events":[{"introduced":"0"},{"fixed":"5.11"}]},{"events":[{"introduced":"0"},{"last_affected":"14.04"}]},{"events":[{"introduced":"0"},{"last_affected":"16.04"}]},{"events":[{"introduced":"0"},{"last_affected":"18.04"}]},{"events":[{"introduced":"0"},{"last_affected":"20.04"}]}],"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2020-16120.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N"}]}