XCCDF tailoring

I would like to informally introduce the concept of XCCDF tailoring because it is not used as much as I would like and I believe the reason is that it is mostly undocumented. We have to go through some basics first.

XCCDF Profile

Profiles are an XCCDF feature that can select / deselect rules and change values that are inputs of the rules (e.g.: password length, various delays, etc… different profiles can have different values without creating multiple rules for the same thing). Even though profiles can change values that act as input to rules we will only deal with selection in this document for simplicity.
Profiles are part of the XCCDF file, the element that specifies them is called <xccdf:profile>.


<Profile id="xccdf_org.open-scap_profile_unselecting">
  <select idref="xccdf_moc.elpmaxe.www_rule_1" selected="false"/>
This profile unselects rule number 1 that is (presumably) selected by default.

Profile inheritance

Every profile can act as an ancestor to another profile. The attribute that is used for this is called @extends.


<Profile id="xccdf_org.open-scap_profile_anti_unselecting" extends="xccdf_org.open-scap_profile_unselecting">
  <title>Not Really Unselecting</title>
  <select idref="xccdf_moc.elpmaxe.www_rule_1" selected="true"/>

Tailoring is a process that affects profiles in an XCCDF without changing the XCCDF file itself. So if it is signed, sha1-ed or otherwise officially “frozen”, you can select/deselect a rule without making any of the signatures invalid.

Other situation where tailoring is suitable is when you have a company-wide policy but one rule of it does not make sense for one particular machine, or perhaps you want to enforce stricter rules on public facing servers? In general you want to make slight temporary (revertible) tweaks to the profile you are using for whatever reason.

Result of tailoring is a tailoring file which is supposed to be used with the XCCDF file for evaluations.


<?xml version="1.0" encoding="UTF-8"?>
<Tailoring xmlns="http://checklists.nist.gov/xccdf/1.2" id="xccdf_org.open-scap_tailoring_example">
  <version time="2013-01-15T16:00:00.000+02:00">1.0</version>
  <Profile id="xccdf_org.open-scap_profile_anti_unselecting" extends="xccdf_org.open-scap_profile_unselecting">
    <title>Not Really Unselecting</title>
    <select idref="xccdf_moc.elpmaxe.www_rule_1" selected="true"/>

using oscap with tailoring:

oscap xccdf eval --tailoring-file some-xccdf-tailoring.xml some-xccdf.xml

Inheritance and tailoring:

XCCDF Tailoring file can contain profiles created from scratch that do not extend any profile in the XCCDF but this situation is fairly rare. The most usual use case is to inherit some profile and select or deselect a couple of rules. This is a very convenient way to make minor adjustments to tailor the profile to your specific needs. The tailoring in the example above inherits a profile in XCCDF and selects a deselected rule.

scap-workbench and tailoring

Tailoring is the only way to change profiles in the new scap-workbench, for simplicity it is called profile customization in the application to make it more accessible to people not well versed in the SCAP nomenclature.
Creating tailoring files by hand is fairly tedious and error prone. Fortunately, you can now do it conveniently in scap-workbench!
First we open the content that we want to use for scanning, in this example case it is scap-security-guide.
The right profile has to be selected (this is the profile that will be tailored). In the screenshot above the ‘Example Server Profile’ that we wanted tailored is already selected.
After clicking the Customize button a new window pops up. Notice how the profile is called Example Server Profile [TAILORED] now. Workbench automatically changes the name to make it obvious that this profile is the tailored profile.
Users can navigate this window to see all the rules, the checkboxes next to rules allow them to select or deselect any given Rule. Addition of  elements happens under the hood automatically.
After tailoring is finished click Finish tailoring.
We can now perform evaluation, tailor again or save the tailoring to a file that can be used later (even outside scap-workbench!). Click Save Tailoring.

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