CVE-2018-18955

Published: 16 November 2018

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.

From the Ubuntu Security Team

Jann Horn discovered that the Linux kernel mishandles mapping UID or GID ranges inside nested user namespaces in some situations. A local attacker could use this to bypass access controls on resources outside the namespace.

Status

Severity score breakdown

References

• https://ubuntu.com/security/notices/USN-3832-1
• https://ubuntu.com/security/notices/USN-3833-1
• https://ubuntu.com/security/notices/USN-3836-1
• https://ubuntu.com/security/notices/USN-3835-1
• https://ubuntu.com/security/notices/USN-3836-2
• https://www.cve.org/CVERecord?id=CVE-2018-18955
• NVD
• Launchpad
• Debian

Bugs

• https://launchpad.net/bugs/1801924