An issue was discovered in shadow 4.5. newgidmap (in shadow-utils) is setuid and allows an unprivileged user to be placed in a user namespace where setgroups(2) is permitted. This allows an attacker to remove themselves from a supplementary group, which may allow access to certain filesystem paths if the administrator has used "group blacklisting" (e.g., chmod g-rwx) to restrict access to paths. This flaw effectively reverts a security feature in the kernel (in particular, the /proc/self/setgroups knob) to prevent this sort of privilege escalation.
The product specifies permissions for a security-critical resource in a way that allows that resource to be read or modified by unintended actors.
| Link | Tags |
|---|---|
| https://bugs.launchpad.net/ubuntu/+source/shadow/+bug/1729357 | third party advisory issue tracking exploit |
| https://security.gentoo.org/glsa/201805-09 | third party advisory vendor advisory |