Monday, July 30, 2018

Oracle Linux - security hardening - CIS control 1.1.1

As part of ensuring you deploy Oracle Linux 7 in a secure way the CIS benchmark van provide a good guidance. Following the CIS benchmark will ensure that most of the important security hardening topics will be considered. As with most general guidelines, the Oracle Linux 7 CIS benchmark, not all will apply on your specific situation. Having stated that, it is good to consider all the points mentioned in the benchmark and apply them with a comply or explain model.

Within this series of posts we will go through all the Oracle Linux 7 CIS benchmark controls and outline them a bit more than might have been done on the actual CIS benchmark.

control : Create Separate Partition for /tmp

The rational behind this control is : Since the /tmp directory is intended to be world-writable, there is a risk of resource exhaustion if it is not bound to a separate partition. In addition, making /tmp its own file system allows an administrator to set the noexec option on the mount, making /tmp useless for an attacker to install executable code. It would also prevent an attacker from establishing a hardlink to a system setuid program and wait for it to be updated. Once the program was updated, the hardlink would be broken and the attacker would have his own copy of the program. If the program happened to have a security vulnerability, the attacker could continue to exploit the known flaw.

What this in effect means is: that if an attacker would be able to flood /tmp with “junk” data it could lead to a situation where your system disks are full and the operating system is unable to function in the way it should. Additionally, as /tmp is a place most users will be able to write data to an attacker could also write scripts and code to it. As it provides a place to store code it can be abused from that point of view. If you allow users to write to the /tmp space however disallow them to execute code that is stored in /tmp this takes away this specific risk of code execution for code stored in /tmp.

The CIS benchmark provides the below standard code to verify if you have a separate /tmp in place:


grep "[[:space:]]/tmp[[:space:]]" /etc/fstab


Even though this check works the below might be a bit smarter and will provide a pass or fail result based upon the check:

#!/bin/bash

grep "[[:space:]]/tmp[[:space:]]" /etc/fstab | wc -l&> /dev/null
if [ $? == 0 ]; then
   echo "fail"
else
   echo "pass"
fi

In effect the above will do the same as the check promoted in the CIS benchmark document, however, it might be easier to include in a programmatic check. In case /tmp is not a separate file system it will return a fail on this control.

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