Poor Man Central SCAP
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Poor Man Central SCAP


When working with SCAP content for its various use cases, there are already a few open source projects that provide us with SCAP scanners. Open-SCAP is able to test OVAL and XCCDF documents, but only locally (thus far). Ovaldi is a similar one.

What is missing is a way to centrally work on SCAP content, having multiple systems pull the necessary definitions from the central repository, "play" it locally and send back the results to a central location.

There, on this central location, the reports can then be aggregated further to make proper architectural decisions with a wider view on the situation, rather than having to parse the reports individually.

Central management of SCAP content

SCAP 1.2 already provides a way to have a single stream (SCAP data streams) containing all SCAP content needed for a local system to properly test all that is needed.

pmcs will use SCAP data streams by bundling the XCCDF, OVAL, CPE (and in the future other protocols as well) for each target based on a prepared definition, and offering the SCAP data stream as a single HTTP(S) resource. It is however no hard requirement that the data is in SCAP data stream format: we can easily just pass OVAL files and use those as long as they are "contained".

Local SCAP scanners pull the SCAP data stream(s) needed for the system, based on a set of system parameters (hostname, domainname, platform, class and generic keywords). They evaluate the SCAP data stream(s) and send back the reports towards a central repository.

Currently, the two "central" locations supported are regular file systems (in case of file shares), using "file://" as the "remote" pointer, and web servers, using "http://" or "https://" as "remote" pointer.

What pmcs provides

With pmcs, security administrators can manage SCAP scanning across a large set of systems using the local SCAP scanner software (i.e. SCAP scanner software installed on the target system) using a simple wrapper that pulls in the necessary SCAP data streams, runs the necessary tests and sends the results towards a central location again.

Why local SCAP scanner software

Local SCAP scanner software is more available than SCAP scanners that use remote scanning. Tools such as Open-SCAP [http://www.open-scap.org] or Ovaldi [http://sourceforge.net/projects/ovaldi/] are perfectly usable locally and offer a wide set of supported OVAL tests.

Why should I use a centralized approach?

When you are dealing with only a handful of systems, there is no need to centrally manage running SCAP tests. You just have the SCAP content (OVAL or XCCDF files) on those systems and occasionally run the SCAP scanner to get information about the state of your system(s).

But the moment you need to manage this across a large environment, this becomes troublesome:

  • how do you get the SCAP content on all those systems?
  • will you log on on each of those systems to run the scanner if you need to quickly get information about a certain vulnerability?
  • will you go fetch the results on each system towards your workstation to check its results?

By centrally provisioning the SCAP content (which, in case of pmcs, is either on a network share or on a web server) and getting the results (OVAL results or XCCDF test results) back on a central location, the security administrator can focus on creating proper SCAP content and interpreting the SCAP results without having to think about distributing and running the SCAP content on all systems.

How do I configure pmcs

One of the focus areas of pmcs is that the local components use SCAP scanners already available. The first focus is on Open-SCAP and Ovaldi, but others should be easy to integrate as we are focusing on the SCAP technologies.

The local pmcs agent has two roles: scheduling regular SCAP evaluations, and waiting for triggers to do ad-hoc evaluations.

The scheduled evaluation is no daemonized agent; it has to be scheduled from a scheduler such as Cron, Windows Task Scheduler or even more enterprise job schedulers. But we will support the daemonized approach as well where the admin can trigger evaluations.

Only a single parameter should be passed on to the agent: the URN towards the central configuration repository. For instance (pmcsa = pmcs agent):

~$ pmcsa https://cscapserver.localdomain/repo

The agent will then pull in the necessary information from this location. This is one of the advantages of pmcs - it uses a configuration-less approach to handling the scanners. Well, not exactly configuration-less, but the configuration is also managed centrally.

Once information is obtained, the agent will download the SCAP content that it needs to evaluate, evaluate it, and send the results to a central repository (which does not need to be the same URN as the central configuration repository).

I can ask for immediately executed scans?

Sometimes administrators want to push out certain checks towards one or more systems without having to wait for a particular scheduled run. We need to support this, which means that the pmcsa (pmsc agent) will also support a daemonized setup to which administrators can push evaluation requests.

How to scan remote systems

Later editions of pmcsa will support remote scanning as well. In these setups, the pmcsa agent pulls in the remote list. This list contains the evaluations (xccdf or oval) that need to be done, but also an additional parameter called the target list.

This target list contains the ID of the target, the encryption type of the remainder of the data, and then a list of key/value pairs which will be used as environment variables. That means that the scans that will be executed (one for each ID) will be done with the given environment variables loaded.

What pmcs does not provide

With pmcs, you do not get any tools or methods for creating the SCAP content itself (although pointers are given as simple scripts and documents) nor will you get tools (yet) that help process the results.

Generating SCAP content

Generating SCAP content can be achieved either by directly downloading it from one of the SCAP repositories (just use your favorite search engine and look for "oval repository" or so) or creating it yourself with an XML editor (or just a simple text editor).

If you downloaded OVAL files, a script is provided in pmcs that creates an XCCDF file that refers to all tests in the OVAL files. This is not needed in order to run OVAL scans, but if you want to create a SCAP data stream using open-scap, you need an XCCDF file:

~$ oscap ds sds-compose my-xccdf-file.xml

Parsing and interpreting OVAL and XCCDF results

The result files sent back from the targets still needs to be interpreted. The easiest way is to directly build the reports from the files, which you can do using ovaldi or open-scap or any of the other SCAP tools that provide reports.

As the files are XML files, anyone with some XSL expertise can build their own reports on the results.

We might add in a component to pmcs later to support reporting on the results, but for now the only provided methods are quite ugly and are mostly as try-outs.

Needed expertise

In order to use pmcs, you will need to have some understanding of how the Security Content Automation Protocols work and be able to work with at least one SCAP scanner software item.

External software requirements

The pmcs setup wouldn't be a "poor man" setup if we wouldn't leverage existing infrastructure as much as possible.

  • To build the SCAP data streams, we assume the administrator does this himself. This can be accomplished with tools such as open-scap.
  • The first central repositories are simple HTTP directory structures; pmcs will provide a few scripts to easily manage those, such as creating the proper directory structure.
  • The target repository to save files in will, at first, be a simple CGI script to run on a web server. Authentication against the repositories is assumed to be handled using the system's server certificates if applicable.
  • The pmcsa script (currently) relies on curl, wget and nc (netcat) on Unix to support its endeavors for network-related activities.