The following is a description of the elements, types, and attributes that compose the core schema for encoding Open Vulnerability and Assessment Language (OVAL) System Characteristics. The Core System Characteristics Schema defines all operating system independent objects. These objects are extended and enhanced by individual family schemas, which are described in separate documents. Each of the elements, types, and attributes that make up the Core System Characteristics Schema are described in detail and should provide the information necessary to understand what each object represents. This document is intended for developers and assumes some familiarity with XML. A high level description of the interaction between these objects is not outlined here.
The OVAL Schema is maintained by The MITRE Corporation and developed by the public OVAL Community. For more information, including how to get involved in the project and how to submit change requests, please visit the OVAL website at http://oval.mitre.org.
The system_characteristics element is the root of an OVAL System Characteristics Document, and must occur exactly once. Its purpose is to bind together the four major sections of a system characteristics file - generator, system_info, collected_objects, and system_data - which are the children of the oval_system_characteristics element.
Child Elements Type MinOccurs MaxOccurs generator oval:GeneratorType 1 1 system_info oval-sc:SystemInfoType 1 1 collected_objects oval-sc:CollectedObjectsType 0 1 system_data oval-sc:SystemDataType 0 1 ds:Signature n/a 0 1
The SystemInfoType complex type specifies general information about the system that data was collected from, including information that can be used to identify the system. See the description of the InterfacesType complex type for more information. Note that the high level interfaces is required due to the inclusion of the xsd:any tag that follows it. The interfaces tag can be empty if no single interface is present.
Additional system information is also allowed although it is not part of the official OVAL Schema. Individual organizations can place system information that they feel is important and these will be skipped during the validation. All OVAL really cares about is that the required system information items are there.
Child Elements Type MinOccurs MaxOccurs os_name xsd:string 1 1 os_version xsd:string 1 1 architecture xsd:string 1 1 primary_host_name xsd:string 1 1 interfaces oval-sc:InterfacesType 1 1
The InterfacesType complex type is a container for zero or more interface elements. Each interface element is used to describe an existing network interface on the system.
Child Elements Type MinOccurs MaxOccurs interface oval-sc:InterfaceType 0 unbounded
The InterfaceType complex type is used to describe an existing network interface on the system. This information can help identify a specific system on a given network.
Child Elements Type MinOccurs MaxOccurs interface_name xsd:string 1 1 ip_address xsd:string 1 1 mac_address xsd:string 1 1
The CollectedObjectsType complex type states all the objects that have been collected by the system characteristics file. The details of each object are defined by the global OVAL object that is identified by the id.
Child Elements Type MinOccurs MaxOccurs object oval-sc:ObjectType 1 unbounded
The ObjectType complex type provides a reference between items collected and a related global OVAL Object.
If an OVAL Object does not exist on the system, then an object element is still provided but with the flag attribute set to 'does not exist' and with no reference child elements. This shows that the object was looked for but not found on the system. If no object element is written in this case, users of the system characteristics file will not know whether the object was not found or no attempt was made to collect it.
The required id attribute is the id of the global OVAL Object. The required version attribute is the specific version of the global OVAL Object that was used by the data collection engine. The version is necessary so that analysis using a system characteristics file knows exactly what was collected. The optional variable_instance identifier is a unique id that differentiates each unique instance of an object. Capabilities that use OVAL may reference the same definition multiple times and provide different sets of variable values each time the definition is referenced. This will result in multiple instances of an object being included in the OVAL System Characteristics file (definitions that do not use variables can only have one unique instance). The inclusion of a unique instance identifier will allow the OVAL results file to report the correct item associated with an object for each combination of supplied values. The optional comment attribute provides a short description of the object. The required flag attribute holds information regarding the outcome of the data collection. For example, if there was an error looking for items that match the object specification, then the flag would be 'error'. Please refer to the description of FlagEnumeration for details about the different flag values.
Attributes:
- id oval:ObjectIDPattern (required) - version xsd:nonNegativeInteger (required) - variable_instance xsd:nonNegativeInteger (optional -- default='1') - comment xsd:string (optional) - flag oval-sc:FlagEnumeration (required)
Child Elements Type MinOccurs MaxOccurs message oval:MessageType 0 unbounded variable_value oval-sc:VariableValueType 0 unbounded reference oval-sc:ReferenceType 0 unbounded
The VariableValueType complex type holds the value to a variable used during the collection of an object. The required variable_id attribute is the unique id of the variable being identified.
Attributes:
- variable_id oval:VariableIDPattern (required)
Simple Content xsd:anySimpleType
The ReferenceType complex type specifies an item in the system characteristics file. This reference is used to link global OVAL Objects to specific items.
Attributes:
- item_ref oval:ItemIDPattern (required)
The SystemDataType complex type is a container for one or more item elements. Each item defines a specific piece of data on the system.
Child Elements Type MinOccurs MaxOccurs oval-sc:item n/a 1 unbounded
The abstract item element holds information about a specific item on a system. An item might be a file, a rpm, a process, etc. This element is extended by the different component schemas through substitution groups. Each item represents a unique instance of an object as specified by an OVAL Object. For example, a single file or a single user. Each item my be referenced by more than one object in the collected object section. Please refer to the description of ItemType for more details about the information stored in items.
The ItemType complex type specifies an optional message element that is used to pass things like error messages during data collection to a tool that will utilize the information. The required id attribute is an unique (to the file) identifier that allows the specific item to be referenced. The required status attribute holds information regarding the success of the data collection. For example, if an item exists on the system then the status would reflect this with a value of 'exists'. If there was an error collecting any information about an item that is known to exist, then the status would be 'error'. An error specific to a particular entity should be addressed at the entity level and not the item level. Note that an item should not have a status of 'does not exist' as there simply would be no item element in the system characteristics file for this case. If part of the object declaration does not exist on the system (say a path exists but the filename does not), then no item should be written for this object and the object element in the collected_object section should have a flag value of 'does not exist'.
Attributes:
- id oval:ItemIDPattern (required) - status oval-sc:StatusEnumeration (optional -- default='exists')
Child Elements Type MinOccurs MaxOccurs message oval:MessageType 0 1
The FlagEnumeration simple type defines the valid flags associated with a collected object. These flags are meant to provide information about how the specified object was handled by the data collector. In order to evaluate an OVAL Definition, information about the defined objects needs to be available. The flags help detail the outcome of attempting to collect information related to these objects..
Value Description error
A flag of 'error' says that there was an error trying to identify objects on the system that match the specified object declaration. This flag is not meant to be used when there was an error retrieving a specific attribute, but rather when it could not be determined if an instance of the object exists or not. Any error in retrieving specific attributes should be represented by setting the status of that specific attribute to 'error'.
complete
Every matching item on the system has been identified and is represented in the system characteristics file. It can be assumed that no additional matching items exist on the system.
incomplete
An instance of the specified object exists on the system, but only some of the matching items have been identified and are represented in the system characteristics file. It is unknown if additional matching items also exist. Note that with a flag of incomplete, each item that has been identified matches the object declaration, but additional items might also exist on the system.
does not exist
A flag of 'does not exist' means that the underlying structure is installed on the system but no matching item was found. For example, the Windows metabase is installed but the specified metabase_object could not be found. In this example, if the metabase itself was not installed, then the flag would have been 'not applicable'.
not collected
An attempt to collect information on items matching the object was not made. An object with this flag will produce an 'unknown' result during analysis since it is unknown if a matching items exists on the system or not. This is different from an 'error' flag since with an 'error' flag an attempt to collect information was made. With the 'not collected' flag, no attempt was made.
not applicable
The specified object is not applicable to the system being characterized. This could be because the data repository is not installed or that the object structure is for a different flavor of systems. An example would be trying to collect objects related to a Red Hat system off a Windows system. Another example would be trying to collect an rpminfo object on a Linux system if the rpm packaging system is not installed. If the rpm packaging system is installed and the specified rpminfo object could not be found, then the flag would be 'does not exist'.
Below is a table that outlines how each FlagEnumeration value effects evaluation of a given test. Note that this is related to the existence of a set of items identified by an object and not each item’s compliance with a state. The left column identifies the FlagEnumeration value in question. The right column specifies the ResultEnumeration value that should be used when evaluating the collected object.
|| flag value || test result is || -----------------||---------------------------- error || error complete || (test result depends on incomplete || check_existence and does not exist || check attributes) not collected || unknown not applicable || not applicable -----------------||-----------------------------
The StatusEnumeration simple type defines the valid status messages associated with collection of specific information associated with an item.
Value Description error
A status of 'error' says that there was an error collecting information associated with an item as a whole or a specific entity.
exists
A status of 'exists' says that the item or specific piece of information exists on the system and has been collected.
does not exist
A status of 'does not exist' says that the item or specific piece of information does not exist and therefore has not been collected. This status assumes that an attempt was made to collect the information, but the information just doesn't exist. This can happen when a certain entity is only pertinent to particular instances, or when xsi:nil is used to refer to a higher level object.
not collected
A status of 'not collected' says that no attempt was made to collect the item or specific piece of information so it is unknown what the value is and if it even exists.
The EntityItemBaseType complex type is an abstract type that defines the default attributes associated with every entity. The optional datatype determines the type of data expected. (the default datatype is 'string') Note that the datatype attribute simply defines the type of data as found on the system, it is not used during evaluation. An OVAL Definition defines how the data should be interpreted during analysis. If the definition states a datatype that is different than what the system characteristics presents, then a type cast must be made. The optional mask attribute is used to identify values that have been hidden for sensitivity concerns. This is used by the result file which uses the system characateristic schema to format the information found on a specific system. If the original definition set the mask attribute of an entity to 'true', then value obtained from the system should not be presented in the results file. A system characteristics file that is not held within a results file should not use the mask attribute. The optional status attribute holds information regarding the success of the data collection. For example, if there was an error collecting a particular piece of data, then the status would be 'error'.
Attributes:
- datatype oval:DatatypeEnumeration (optional -- default='string') - mask xsd:boolean (optional -- default='false') - status oval-sc:StatusEnumeration (optional -- default='exists')
Simple Content xsd:anySimpleType
The EntityItemAnyType type is extended by the entities of an individual item. This type provides uniformity to each entity by including the attributes found in the EntityItemBaseType. This specific type describes any simple data.
Attributes:
Simple Content oval-sc:EntityItemBaseType
The EntityItemBinaryType type is extended by the entities of an individual item. This type provides uniformity to each entity by including the attributes found in the EntityItemBaseType. This specific type describes simple binary data. The empty string is also allowed for cases where there was an error in the data collection of an entity and a status needs to be reported.
The EntityItemBoolType type is extended by the entities of an individual item. This type provides uniformity to each entity by including the attributes found in the EntityItemBaseType. This specific type describes simple boolean data. The empty string is also allowed for cases where there was an error in the data collection of an entity and a status needs to be reported.
The EntityItemFloatType type is extended by the entities of an individual item. This type provides uniformity to each entity by including the attributes found in the EntityItemBaseType. This specific type describes simple float data. The empty string is also allowed for cases where there was an error in the data collection of an entity and a status needs to be reported.
The EntityItemIntType type is extended by the entities of an individual item. This type provides uniformity to each entity by including the attributes found in the EntityItemBaseType. This specific type describes simple integer data. The empty string is also allowed for cases where there was an error in the data collection of an entity and a status needs to be reported.
The EntityItemStringType type is extended by the entities of an individual item. This type provides uniformity to each entity by including the attributes found in the EntityItemBaseType. This specific type describes simple string data.