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Default umask
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21 August 2006
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The default umask (usermask) on most systems should be 022 to ensure that
files are created with the permissions 0644 (-rw-r--r--). To change the
default umask setting for a system, edit /etc/profile to ensure that you umask
is appropriate for your setup. |
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Two SSH configuration options that can be set to improve security should be checked on your production server. UsePrivilegeSeparation is an option, when enabled will allow the OpenSSH server to run a small (necessary) amount of code as root and the of the code in a chroot jail environment. StrictModes checks to ensure that your ssh files and directories have the proper permissions and ownerships before allowing an SSH session to open up. The directives should be set in the /etc/ssh/sshd_config as follows:
UsePrivilegeSeparation yes
StrcitModes yes
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On a production server that is in a common area (although this should not be the case, some situations are inevidable). To avoid an accidental CTRL-ALT-DEL reboot of the machine, do the following to remove the necessary lines from the /etc/inittab file:
# sed -i 's/ca::ctrlaltdel:/#ca::ctrlaltdel:/g' /etc/inittab
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Make use of security tools out there to test your server's weaknesses. Nmap
is an excellent port scanning tool to test to see what ports you have open. On
a remote machine, type the command:
# nmap -sTU
Starting nmap 3.70 ( http://www.insecure.org/nmap/ ) at 2006-08-10 13:51 EST
Interesting ports on eric (172.16.0.1):
(The 3131 ports scanned but not shown below are in state: closed)
PORT STATE SERVICE
22/tcp open ssh
113/tcp open auth
Nmap run completed -- 1 IP address (1 host up) scanned in 221.669 seconds
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Users who may be acting up or aren't listening can still be controlled.
Using a program called 'skill' (signal kill) which is part of the 'procps'
package.
Halt/Stop User eric: skill -STOP -u eric
Continue User eric: skill -CONT -u eric
Kill and Logout User eric: skill -KILL -u eric
Kill and Logout All Users: skill -KILL -v /dev/pts/*
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