Version: 2.2.0.dev0

XML Schema Validation

The stix-validator library provides methods and data types to help perform STIX and CybOX XML Schema validation. The stix-validator library bundles all versions of STIX and CybOX XML Schema files with it, but also supports the ability to validate validate against external directories of schemas or remote, web-accessible schema locations.

The following code examples demonstrate different ways you can utilize the STIX and CyOX XML Schema validation capabilities in stix-validator.

Validating STIX and CybOX Documents

The stix-validator sdv.validate_xml() method can be used to validate STIX and CybOX XML files or file-like objects.

import sdv

# Validate the 'xml-content.xml' STIX/CybOX document using bundled XML schemas.
results = sdv.validate_xml('xml-content.xml')

# Print the result!
print results.is_valid

When validating STIX content, The sdv.validate_xml() method acts as a proxy to the STIXSchemaValidator class and is equivalent to the following:

from sdv.validators import STIXSchemaValidator

# Create the validator instance
validator = STIXSchemaValidator()

# Validate 'xml-content.xml` STIX document using bundled STIX schemas
results = validator.validate('xml-content.xml')

# Print the results!
print results.is_valid

When validating CybOX content, the sdv.validate_xml() method passes its input to the CyboxSchemaValidator class.

The examples above pass the 'xml-content.xml' filename into sdv.validate_xml() and STIXSchemaValidator.validate(), but these methods (and all other validation methods) can also accept file-like objects (such as files on disk or StringIO instances), etree._Element instances, or etree._ElementTree instances. Super duper neato!

Using Non-bundled Schemas

Some STIX data which utilizes STIX extensions may require non-STIX schemas (e.g, OVAL, OpenIOC, etc.) to perform validation. To validate a STIX document which includes non-STIX extension data users can provide a path to a directory containing all the schemas required for validation.

import sdv

# Path to a directory containing ALL schema files required for validation
SCHEMA_DIR = "/path/to/schemas/"

# Use the `schemas` parameter to use non-bundled schemas.
results = sdv.validate_xml('stix-content.xml', schemas=SCHEMA_DIR)


Validating against external schema directories requires that all schemas necessary for validation be found under the directory. This includes STIX schemas!

Using xsi:schemaLocation

XML content that contains an xsi:schemaLocation attribute referring to external schemas can be validated using the xsi:schemaLocation value by making use of the schemaloc parameter,

import sdv

# Use the xsi:schemaLocation attribute to resolve remote schemas
results = sdv.validate_xml('xml-content.xml', schemaloc=True)

# Print the results!
print results.is_valid

STIX and CybOX Versions

The stix-validator is bundled with official STIX and CybOX schemas, which enables validation of STIX and CybOX XML documents without requiring users to provide schemas.

Because we bundle several versions of the STIX and CybOX schemas, the stix-validator needs to know what version of STIX or CybOX to validate input documents against. By default, the stix-validator will attempt to determine the version of the input STIX/CybOX document by inspecting the document for version information.

If the input document contains no version information, users must declare a version for the STIX/CybOX document via the version parameter:

import sdv

# Validate the 'stix-content.xml'.
# Declare that the STIX content is STIX v1.2
results = sdv.validate_xml('stix-content.xml', version='1.2')

# Print the result!
print results.is_valid


No version information is required by the stix-validator when performing validation against non-bundled schemas or when validating using xsi:schemaLocation. Any version values that are passed in will be ignored by the API.

However, the schemas may define constraints or requirements for version numbers, so validation errors regarding invalid or missing version numbers are still reported as XmlSchemaError objects.

Unknown Versions

If a version is not passed in nor found on the document, one of the following UnknownVersionError implementations are raised:

Invalid Versions

If an invalid version is passed in nor found on the document, one of the following InvalidVersionError implementations are raised:

Retrieving XML Schema Validation Errors

The following sections explain how to retrieve XML Schema validation errors from the XmlValidationResults class.

The XmlValidationResults Class

XML Schema validation results are communicated via the XmlValidationResults and XmlSchemaError classes. The sdv.validate_xml() returns an instance of XmlValidationResults.

To determine if a document was valid, users only need to inspect the is_valid property:

import sdv

# Validate the 'xml-content.xml' input document using bundled schemas.
results = sdv.validate_xml('xml-content.xml')

# Print the result!
print results.is_valid

If the is_valid property is False, users can inspect the errors property to retrieve specific validation errors.

The errors property on XmlValidationResults contains a list of XmlSchemaError instances, which hold details about the validation errors and methods for accessing those details.

import sdv

results = sdv.validate_xml('xml-content.xml')

# If 'xml-content.xml' is invalid, print each error
if not results.is_valid:
    for error in results.errors:
        print "Line Number:", error.line
        print "Error Message:", error

Dictionaries and JSON

Users wanting to work with dictionaries or pass around JSON blobs can make use of the XmlValidationResults.as_dict() and XmlValidationResults.as_json() methods.

import sdv

# Validate 'xml-content.xml'
results = sdv.validate_xml('xml-content.xml')

# Retrieve results as dictionary
result_dictionary = results.as_dict()  # returns {'result': True} if valid

# Retrieve results as JSON
result_json = results.as_json() # returns '{"result": true}' JSON if valid