[原文]Vulnerability in union file system in FreeBSD 2.2 and earlier, and possibly other operating systems, allows local users to cause a denial of service (system reload) via a series of certain mount_union commands.
FreeBSD contains a flaw that may allow a local denial of service. The issue is triggered when a malicious user issues a certain sequence of mount_union commands, which may cause a system reload due to a flawed vfsload(3) library call and will result in loss of availability for the platform.
Upgrade to version FreeBSD 2.1-STABLE or FreeBSD 2.2-CURRENT as distributed later than 1996-05-18 or if you are currently running 2.1 or later, as it has been reported to fix this vulnerability. It is also possible to correct the flaw by implementing the following workaround: remove the setuid permission bit from the mount_union and mount_msdos program.
#chmod u-s /sbin/mount_union /sbin/mount_msdos