In FreeBSD 12.0-STABLE before r350261, 12.0-RELEASE before 12.0-RELEASE-p8, 11.3-STABLE before r350263, 11.3-RELEASE before 11.3-RELEASE-p1, and 11.2-RELEASE before 11.2-RELEASE-p12, system calls operating on file descriptors as part of mqueuefs did not properly release the reference allowing a malicious user to overflow the counter allowing access to files, directories, and sockets opened by processes owned by other users.
https://security.netapp.com/advisory/ntap-20190814-0003/
https://security.FreeBSD.org/advisories/FreeBSD-SA-19:24.mqueuefs.asc
https://security.FreeBSD.org/advisories/FreeBSD-SA-19:15.mqueuefs.asc
https://seclists.org/bugtraq/2019/Aug/35
http://packetstormsecurity.com/files/154172/FreeBSD-Security-Advisory-FreeBSD-SA-19-24.mqueuefs.html
http://packetstormsecurity.com/files/153752/FreeBSD-Security-Advisory-FreeBSD-SA-19-15.mqueuefs.html