Check for changes to setuid programs
checksecurity
The checksecurity command scans the mounted files systems (subject to the filter defined in /etc/checksecurity.conf) and compares the list of setuid programs to the list created on the previous run. Any changes are printed to standard output. Also, it generates a list of nfs and afs filesystems that are mounted insecurely (i.e. they are missing the nodev and either the noexec or nosuid flags).
checksecurity is run by cron on a daily basis, and the output stored in /var/log/setuid/setuid.changes.
The checksecurity.conf file defines several configuration variables: CHECKSECURITY_FILTER, CHECKSECURITY_NOFINDERRORS, CHECKSECURITY_NONFSAFS, CHECKSECURITY_EMAIL, CHECKSECURITY_DEVICEFILTER, CHECKSECURITY_PATHFILTER, and LOGDIR. Each is described below.
The CHECKSECURITY_FILTER environment variable which is the argument of 'grep -vE' applied to the output of the mount command. In other words, the value of CHECKSECURITY_FILTER is a regular expression that removes matching lines from those file systems that will be scanned. The default value removes all file systems of type proc, bind, msdos, iso9660, ncpfs, nfs, afs, smbfs, auto, ntfs, coda file systems, anything mounted on /dev/fd*, anything mounted on /mnt or /amd, and anything mounted with option nosuid or noexec.
The checksecurity.conf file is sourced from checksecurity, so you could do some fairly tricky things to define CHECKSECURITY_FILTER.
The CHECKSECURITY_NOFINDERRORS environment variable, if set to the literal "TRUE", disables find errors from checksecurity (actually, it re-routes them to /dev/null ).
The CHECKSECURITY_NONFSAFS environment variable, if set to the literal "TRUE", disables the message about nfs and afs file systems that are mounted without the nodev and either the noexec or nosuid options.
If set, the CHECKSECURITY_EMAIL variable defines who is sent a copy of the setuid.changes file.
The CHECKSECURITY_DEVICEFILTER variable specifies a find clause for which matching block and character device files will not be monitored for changing owners and permissions. For example, if you don't want to check for permission changes on tty device files beneath /dev, you could set the following:
CHECKSECURITY_DEVICEFILTER='-path /dev/tty*'
Note that any added or modified suid programs under that path would still be detected. If you want to specify multiple expressions, separate them with '-o', but there is no need to surround the whole clause with parentheses. To disable this filter, specify it as '-false' (which is the default).
Note that if the system gets restarted often checksecurity will report a lot of changes in the /dev/ subdirectory due to timestamp changes. In this case you might want to change it to:
CHECKSECURITY_DEVICEFILTER='-path /dev/'
The CHECKSECURITY_PATHFILTER variable specifies a find clause which will be pruned from the search path. This means that the entire subtree will be completely skipped. Thus, specifying
CHECKSECURITY_PATHFILTER='-path /var/ftp'
then the entire /var/ftp tree will be skipped. To disable this filter, specify it as '-false' (which is the default).
LOGDIR sets the name of the directory which stores the files which track the permission and ownership changes. By default, they are in /var/log/setuid.
/etc/checksecurity.conf
checksecurity configuration file
/var/log/setuid/setuid.today
setuid files from the most recent run
/var/log/setuid/setuid.yesterday
setuid files from the previous run