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It's important to ensure that your system files are not open for casual editing by users and groups who are not eligible to modify them. Unix separates access control on files and directories according to three characteristics: owner, group, and other. There is always exactly one owner, any number of members of the group, and everyone else.
Default filesystem for Red Hat (ext3) supports ACL with stock 2.6 kernel. Default filesystem for Suse 9 and 10(riesner) support only standard Unix file permissions.
There are several issue in file permission hardening
@users hard core 0 @users hard nproc 50 @users hard rss 5000
This says to prohibit the creation of core files, restrict the number of processes to 50, and restrict memory usage per user to 5M.
You can also use the /etc/login.defs configuration file to set the same limits.
Find all SUID/SGID programs on your system, and keep track of what they are, so you are aware of any changes which could indicate a potential intruder. Use the following command to find all SUID/SGID programs on your system. You can remove the SUID or SGID permissions on a suspicious program with chmod, then restore them back if you absolutely feel it is necessary.
root# find / -perm -2 ! -type l -lsand be sure you know why those files are writable. In the normal course of operation, several files will be world-writable, including some from /dev, and symbolic links, thus the ! -type l which excludes these from the previous find command.
root# find / \( -nouser -o -nogroup \) -print
find /home -name .rhosts -print
# Set the user's default umask umask 033Be sure to make root's umask 077, which will disable read, write, and execute permission for other users, unless explicitly changed using chmod. In this case, newly-created directories would have 744 permissions, obtained by subtracting 033 from 777. Newly-created files using the 033 umask would have permissions of 644.
If you are using Red Hat, and adhere to their user and group ID creation scheme (User Private Groups), it is only necessary to use 002 for a umask. This is due to the fact that the default configuration is one user per group.
It's important to ensure that your system files are not open for casual editing by users and groups who shouldn't be doing that. See World writable files problem
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