Conversion Issues¶
This section discusses some techniques to facilitate the conversion of STIX 1.x data to STIX 2.0. These techniques cover non-obvious issues that might present an impediment to re-using STIX 1.x data.
Assumptions¶
Timestamps, Identifiers and Object Creators¶
In STIX 1.x most properties were optional. This includes properties that
correspond to required properties in STIX 2.0. In particular, all STIX
Objects in 2.0 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 2.0 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 2.0 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 2.0 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 2.0 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 2.0 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 2.0 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 2.0 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 2.0 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 2.0 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 2.0, which could be undesirable.
Optional vs. Required¶
Certain fields are required in STIX 2.0 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 2.0 have certain restrictions that didn’t explicitly appear in STIX 1.x. A pattern in STIX 2.0 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 2.0.
Additionally, the use of the NOT operator in STIX 2.0 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 2.0,
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 2.0 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.