{"id":"CVE-2018-18955","details":"In the Linux kernel 4.15.x through 4.19.x before 4.19.2, map_write() in kernel/user_namespace.c allows privilege escalation because it mishandles nested user namespaces with more than 5 UID or GID ranges. A user who has CAP_SYS_ADMIN in an affected user namespace can bypass access controls on resources outside the namespace, as demonstrated by reading /etc/shadow. This occurs because an ID transformation takes place properly for the namespaced-to-kernel direction but not for the kernel-to-namespaced direction.","modified":"2026-03-15T22:19:43.775464Z","published":"2018-11-16T20:29:00.233Z","references":[{"type":"WEB","url":"https://support.f5.com/csp/article/K39103040"},{"type":"ADVISORY","url":"https://security.netapp.com/advisory/ntap-20190416-0003/"},{"type":"ADVISORY","url":"https://usn.ubuntu.com/3836-2/"},{"type":"ADVISORY","url":"http://www.securityfocus.com/bid/105941"},{"type":"ADVISORY","url":"https://usn.ubuntu.com/3832-1/"},{"type":"ADVISORY","url":"https://usn.ubuntu.com/3833-1/"},{"type":"ADVISORY","url":"https://usn.ubuntu.com/3835-1/"},{"type":"ADVISORY","url":"https://usn.ubuntu.com/3836-1/"},{"type":"FIX","url":"https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.19.2"},{"type":"FIX","url":"https://github.com/torvalds/linux/commit/d2f007dbe7e4c9583eea6eb04d60001e85c6f1bd"},{"type":"FIX","url":"https://www.exploit-db.com/exploits/45886/"},{"type":"FIX","url":"https://bugs.chromium.org/p/project-zero/issues/detail?id=1712"},{"type":"FIX","url":"http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=d2f007dbe7e4c9583eea6eb04d60001e85c6f1bd"},{"type":"FIX","url":"https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.18.19"},{"type":"EVIDENCE","url":"https://www.exploit-db.com/exploits/45915/"}],"affected":[{"database_specific":{"unresolved_ranges":[{"events":[{"introduced":"4.15"},{"fixed":"4.19.2"}]},{"events":[{"introduced":"0"},{"last_affected":"16.04"}]},{"events":[{"introduced":"0"},{"last_affected":"18.04"}]},{"events":[{"introduced":"0"},{"last_affected":"18.10"}]}],"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2018-18955.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}