Remediation through SCAP


Sven Vermeulen Fri 20 December 2013

I promised in my previous post to give some information about remediation.

Remediation is the process where you fix a system to become compliant again after finding out there is a violation on the system. The easiest form of remediation of course is to just notify the administrator and give him the instructions to fix the problem - and in the majority of cases, this is exactly what you will do, considering that automatically fixing things might create more breakage if you are not careful.

But suppose that you know, for a few rules, what the remediation really should be, and you want to automate it. Well, in that case, you can document the remediation (the commands or scripts) in the XCCDF document. As you might have noticed in the previous example, this is handled through a <fix> entity.

In the fix, we mention how the fix should be executed (urn:xccdf:fix:system:commands is to tell the XCCDF interpreter that the remediation are commands executed on the command line (or verbatim within a script). The platform attribute allows us to differentiate based on the platform (or even version of the platform). The other attributes, such as complexity, disruption and reboot is metadata that helps in deciding which auto-remediation you want to execute.

With openscap, the remediation can be triggered online during the evaluation, by adding --remediate

~$ oscap xccdf eval --remediate --profile ${PROFILE} --cpe gentoo-cpe.xml --results results-test-xccdf.xml test-xccdf.xml
Title   There should be no /dev/ROOT in /etc/fstab
Result  pass

Title   There should be no /dev/BOOT in /etc/fstab
Result  pass

Title   rc_sys should be defined in /etc/rc.conf
Result  fail

 --- Starting remediation ---
Title   rc_sys should be defined in /etc/rc.conf
Result  fixed

And indeed, the file has been changed and now complies with the rules again.

We can also generate the remediation scripts offline:

~$ oscap xccdf eval --profile ${PROFILE} --results results-test-xccdf.xml --cpe gentoo-cpe.xml test-xccdf.xml
~$ oscap xccdf generate fix --output results-test-xccdf.xml

The resulting script then contains the steps to remediate the failures reported in the results-test-xccdf.xml file.

In general however, auto-remediation is not that recommended. The amount of effort you put in creating remediation scripts that are safe to execute is huge. If you do this for a single system, it is much easier to just remediate manually. If you need to do it for a large set of systems, it makes more sense to use a configuration management solution like ansible or puppet.

So, now that we have experience with documenting our best practices and running validation, I'll talk about OVAL in the next post.

This post is part of a series on SCAP content:

  1. Documenting security best practices - XCCDF introduction
  2. An XCCDF skeleton for PostgreSQL
  3. Documenting a bit more than just descriptions
  4. Running a bit with the XCCDF document