Gentoo Linux Security Advisory GLSA 200606-02 – When the mailbox is created in useradd, the open() function does not receive the three arguments it expects while O_CREAT is present, which leads to random permissions on the created file, before fchmod() is executed. Versions less than 4.0.15-r2 are affected.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/47170/glsa-200606-02.txt
Source: https://packetstormsecurity.com/files/47170/Gentoo-Linux-Security-Advisory-200606-2.html