​Conversion Issues

This section discusses some techniques to facilitate the conversion of STIX 1.x data to STIX 2.x. These techniques cover non-obvious issues that might present an impediment to re-using STIX 1.x data.


Timestamps, Identifiers and Object Creators

In STIX 1.x most properties were optional. This includes properties that correspond to required properties in STIX 2.x. In particular, all STIX Objects in 2.x are required to have id, created and modified properties. These are often not specified in a STIX 1.x object, but can sometimes be inferred from another STIX 1.x object in the same package.

Content in STIX 1.x was often hierarchical unlike content in STIX 2.x which is relatively flat, and this can help to determine required properties. For instance, a timestamp on a STIX 1.x package could be construed as the timestamp for all objects it contains. Likewise, an object could assume that its parent object’s timestamp is also the timestamp of that object, unless that object possessed its own timestamp. Of course, if no timestamp is present for any of the objects, included the top level package, some other timestamp outside of the content must be used. In most cases, this would probably result in using the current timestamp when the conversion is made.

Most top-level STIX 1.x objects contained an id (or an idref), however when converting STIX 1.x TTPs and Exploit Targets the id must be assigned to the STIX 2.x object that results. For instance, a TTP might have contain an attack pattern object, but the id was not a property of the attack pattern, but the TTP.

In certain circumstances, no id is available or in the case of TTPs and Exploit Targets, there may be more than one STIX 2.x object created. In these cases, a new id must be used.

In STIX 1.x, all top-level objects had a Information_Source property to hold information about, among other things, the object creator. However, this property was optional. created_by_ref, which is a common property on all STIX 2.x Objects, is also optional. It should be noted however, that the object creator can also be “inherited” from its parent object, as with the timestamp. This fact can be useful to derive a more robust STIX 2.x object.

Special Considerations for TTPs and Exploit Target Conversions

When converting a STIX 1.x TTP or Exploit Target certain properties exist at the top-level, and not in the subsidiary object which will form the basis of the STIX 2.x object. However, those properties must be used when creating the subsidiary object. See section Attack Pattern for an example. The conversion of that STIX 1.x TTP will yield a STIX 2.x Attack Pattern, whose name and created_by_ref are determined from the TTP itself, and not the STIX 1.x Attack Pattern.

Minor Issues

  • The condition property was optional in STIX 1.x Observables. If it was not specified for an Observable used for patterning, the condition used in the STIX 2.x pattern will be assumed to be “=”.
  • The title property should be used for the name property, when necessary.
  • STIX 1.2 introduced versioning of objects. Currently, there is no guidance to converting STIX 1.2 versioning to STIX 2.x versioning. In most cases, a STIX 1.x relationship between object instances of the same type will be converted to a related-to relationship in STIX 2.x, which could be undesirable.

Optional vs. Required

Certain fields are required in STIX 2.x object that were optional in STIX 1.x. This goes beyond the properties such as ids, created/modified timestamps. The most frequently occurring example is the labels property (also a common property). The elevator will use a default value - unknown.

​Issues with Patterns

Patterns in STIX 2.x have certain restrictions that didn’t explicitly appear in STIX 1.x. A pattern in STIX 2.x has explicit rules about if the expression can refer to only one or many observed data instances. Because STIX 1.x patterns did not have any of these restrictions, a reasonable conversion of the pattern by the elevator might be illegal in STIX 2.x.

Additionally, the use of the NOT operator in STIX 2.x is restricted to be used only with Comparison operators. Therefore, it is not possible to express a pattern such as NOT (file.name == foo.bar" AND 'file.size == 123) directly. To yield an equivalent pattern expression in STIX 2.x, DeMorgan’s Law would need to be used to reduce the scope of the NOT operator: (file.name != foo.bar" OR 'file.size != 123), but the elevator does not perform this functionality.

​Single vs. Multiple

Some properties in STIX 1.x allowed for multiple values, but the corresponding property in STIX 2.x does not. In these cases, the first value is used.

In certain situations, something specific to the properties can be helpful in handling this issue. For instance, the first entry in the STIX 1.x Threat Actors motivation property should be assumed to be the primary_motivation. Any others should be listed in the secondary_motivations property.

Data Markings

The stix-elevator currently supports global markings and object-level markings. Through the use of hashing, the elevator make the best effort to detect duplicate markings to prevent excessive object creation. Also, the marking types supported by the elevator is limited to: Simple, Terms of Use, TLP and AIS.