CVE ID:	CVE-2018-18955
Description:	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.
Test IDs:	None available
Cross References:	Common Vulnerability Exposure (CVE) ID: CVE-2018-18955 BugTraq ID: 105941 http://www.securityfocus.com/bid/105941 https://www.exploit-db.com/exploits/45886/ https://www.exploit-db.com/exploits/45915/ http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=d2f007dbe7e4c9583eea6eb04d60001e85c6f1bd https://bugs.chromium.org/p/project-zero/issues/detail?id=1712 https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.18.19 https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.19.2 https://github.com/torvalds/linux/commit/d2f007dbe7e4c9583eea6eb04d60001e85c6f1bd https://usn.ubuntu.com/3832-1/ https://usn.ubuntu.com/3833-1/ https://usn.ubuntu.com/3835-1/ https://usn.ubuntu.com/3836-1/ https://usn.ubuntu.com/3836-2/