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Poor Man Central SCAP Design


pmcs uses four components

  • The central configuration repository stores the configuration entries for the various hosts and the SCAP content to be executed against the target systems. The configuration files are stored in a config/ folder whereas the streams are stored in a stream/ folder.
  • The pmcs agent is a locally-executed script that, if executed in scheduled mode, will pull in the configuration from the central configuration repository and then download the stream(s) that are applicable to the system. Then a local SCAP scanner is used to evaluate the streams after which the pmcs agent sends the results to a central result repository
  • On the local system a local SCAP scanner has to be installed. pmcs does not provide such a scanner, but has been succesfully tested with open-scap and ovaldi. Any SCAP scanner that can be triggered using command-line should be easily supported - all that is needed is to put the right command in the (centrally managed) configuration.
  • The central result repository captures the OVAL and XCCDF results for further processing.

Central configuration repository

The central configuration repository holds the configuration files of the targets as well as the SCAP content to be evaluated on the targets.

Configuration files

The configuration files are stored in a config/ folder; the pmcs agent will look for various configuration entries, starting from a course-grained setting (based on the network DNS domain name) up to the host-specific variables.

This allows administrators to set general parameters (such as the command to evaluate SCAP content) at a high level, while setting particular variables on a per-host system.

The pmcs agent will fetch the configuration from the following set of URIs, in the given order, and will evaluate all entries. All variables, except for keyword=, will be overruled by the settings in the later evaluated configuration files.

  • config/domains/${DOMAIN}.conf
  • config/classes/${CLASS}.conf
  • config/domains/${DOMAIN}/classes/${CLASS}.conf
  • config/hosts/${FQDN}.conf

The variables in this list are captured from the host itself by pmcs:

  • ${DOMAIN} is the DNS domain name of the system. On a Unix system, this is obtained through the dnsdomainname command. If no domainname is provided, the script will use "localdomain".
  • ${CLASS} is the SCAP class to which the system belongs; valid families currently are unix and windows.
  • ${FQDN} is the fully qualified domain name of the system.

The configuration files can/should set the following variables:

  • platform= to set the platform of a system. Examples:
platform=Gentoo Linux
platform=Microsoft Windows 2013 Server
  • resultrepo= to set the target location where OVAL and XCCDF results should be sent to. Examples:
  • scapscanneroval= and scapscannerxccdf= are the command line instructions to evaluate the OVAL or XCCDF content. These instructions are executed when the configuration (which will be discussed later) passes on the OVAL id or XCCDF profile to be evaluated against.
  • scapscanneroval_noid= and scapscannerxccdf_noprofile= is similar to scapscanneroval= and scapscannerxccdf= but for when no OVAL id or XCCDF profile is provided. Examples:
scapscannerxccdf=oscap xccdf eval --profile @@STREAMID@@ --oval-results --results @@XCCDFRESULTNAME@@ @@STREAMNAME@@
scapscannerxccdf_noprofile=oscap xccdf eval --results @@XCCDFRESULTNAME@@ @@STREAMNAME@@
scapscanneroval=oscap oval eval --id @@STREAMID@@ --results @@OVALRESULTNAME@@ @@STREAMNAME@@
scapscanneroval_noid=oscap oval eval --results @@OVALRESULTNAME@@ @@STREAMNAME@@
  • keywords= is an append-only variable (i.e. it is never overruled, only appended to) that administrators can use to "tag" certain systems (or set of systems) allowing for a more granular approach to SCAP scanning across a large set of systems. The variable is comma-separated. Examples:

Streams and stream lists

Next, the pmcs agent will get an overview of SCAP data streams that it needs to evaluate. The lists are obtained through the following URIs (all hits are evaluated).

  • stream/hosts/${FQDN}/remotes.conf
  • stream/hosts/${FQDN}/list.conf
  • stream/domains/${DOMAIN}/classes/${CLASS}/platforms/${PLATFORM}/list.conf
  • stream/domains/${DOMAIN}/classes/${CLASS}/list.conf
  • stream/classes/${CLASS}/platforms/${PLATFORM}/list.conf
  • stream/classes/${CLASS}/list.conf
  • stream/domains/${DOMAIN}/list.conf
  • stream/keywords/${KEYWORD}/list.conf

The ${PLATFORM} variable is the one assigned through the configuration (as mentioned earlier) but where special characters (such as spaces) are changed with underscores.

The URI with ${KEYWORD} is evaluated for each keyword assigned to the system.

The remotes.conf file is used to identify remote targets to scan, whereas list.conf contains the local scanning.

list.conf syntax

The list.conf file obtained from the repository uses the following syntax:

  • The <type> is either oval or xccdf and informs the pmcs agent which type of SCAP content is going to be evaluated.
  • The <resultid> is a unique identifier that identifies how the result files should be stored. XCCDF results will be stored as <resultid>-xccdf-results.xml whereas OVAL results are stored as <resultid>-oval-results.xml.
  • The <streamfile> is the relative URI, starting from the stream/ folder, that the agent will need to fetch.
  • The <id> is an optional identifier telling the agent what OVAL id or XCCDF profile should be used.

An example list file:


remotes.conf syntax

The remotes.conf file obtained from the repository uses the following syntax:


The added <targetlist> is a relative URL within the configuration repository pointing to the list of targets.

target list syntax

The target list uses the following syntax:

  • The <targetid> is a unique identifier for the target. For instance, if remote scanning is used for LDAP servers, this could be ldap/serv1 , ldap/serv2, etc.
  • The <encryptiontype> is the type of encryption used in the <environmentlist>. It could be just clear if there is no encryption, or openssl-aes=<id> if it uses an openssl-encrypted string.
  • The <environmentlist> is, if decrypted, in a key-value set, comma separated with (mandatory) quotes, like so: ENV1="value1",ENV2="value2",....

The encryption is handled by openssl if openssl-aes=<id> is given. The <id> value is a simple string used to find the proper key. The location of the keys is given through the PMCS_AESKEY_ environment variable.

pmcs agent

The pmcs agent is a simple script that pulls the information from the central configuration repository, evaluates the streams and then sends the results to a central result repository.

More details about its design (including pseudo-code) can be found in the bin/pmcsa directory.

Local SCAP scanner

For local SCAP scanning, tools such as open-scap (oscap) or ovaldi can be used.

Central result repository

The central result repository obtains the result files from the systems and stores them on its file system. Although definitely not mandatory, the following hierarchical structure can help simplify reporting later:

  `- <date>
     `- <host>

If you need post-processing on the results, it makes sense that all results for a particular day are contained within a single directory tree.