A large part of the reason for doing threat actor attribution and correlation is to develop an understanding of the adversary behavior in order to better prioritize courses of action and defend against those types of attacks. In many cases, adversary behavior can be characterized by the types of attack patterns they typically use: for example, using spear phishing as a delivery mechanism for malware is an attack pattern. In other cases, behavior can be described based on the malware that the adversary typically uses.
This scenario represents a threat actor known as “Adversary Bravo”. Adversary Bravo is known to use phishing attacks to deliver remote access malware to the targets. The malware variety they typically use is a variant on the Poison Ivy malware.
The threat actor representation itself is fairly simple for this idiom: the
Title is set to “Adversary Bravo” and the basic STIX identity construct is used to name the threat actor. Unlike the threat actor group identity idiom, in this case the CIQ extension to the identity extension point is not used. Not enough is known about this particular threat actor to justify using CIQ (or, more likely, the organization producing this STIX does not deal with threat actor identity information) so the simple
Name field is used instead.
Adversary behavior, including attack patterns and malware, are represented in STIX using the TTP component’s
Behavior field. Malware can be described at a high level by using the basic
Malware Instance field and the MalwareInstanceType. For this PIVY variant, the
Name is set to “Poison Ivy Variant d1c6” and the
Type field is set to “Remote Access Trojan”, which is a value in the default STIX vocabulary for that field (MalwareTypeVocab-1.0). More advanced usages of this type are demonstrated in the MAEC characterization idiom, which describes how to use the same structure to fully describe the malware’s behavior using Malware Attribute Enumeration and Characterization (MAEC).
It’s technically possible to use a single TTP to represent both an attack pattern and a piece of malware, however combining distinct concepts into single components makes pivoting data in the future much more difficult. For example, if it’s later determined that the same PIVY variant is used by a different threat actor it’s useful to have it in a separate TTP in order to relate both threat actors to it (and only Adversary Bravo to the attack pattern). To make sure this works from the start, it’s generally better to split distinct concepts into separate components. This primarily comes up in representing TTPs but the same suggestion holds true for all components.
So rather than adding an attack pattern section to the malware TTP, a new TTP was used that contains just the attack pattern. The attack pattern, described using AttackPatternType, contains a
CAPEC ID and a
Description. Common Attack Pattern Enumeration and Classification (CAPEC™) is a dictionary of potential attack patterns, so in this case by looking in that dictionary the producer was able to see that “CAPEC-98” is the ID for phishing. The best way to find the correct CAPEC is to use a generic search engine like Google or to use the CAPEC website. Other than just the CAPEC ID, the attack pattern
Description field is used to clearly and simply convey that CAPEC-98 is “Phishing”.
Observed TTP list inside the threat actor is used to relate the threat actor to the two TTPs. For the malware TTP, the
Relationship descriptor “Leverages Malware” is used while for the attack pattern TTP “Leverages Attack Pattern” is used.
Taken together, the three constructs represent the threat actor and the known malware/attack patterns leveraged by that actor.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 <stix:TTPs> <stix:TTP id="example:ttp-8ac90ff3-ecf8-4835-95b8-6aea6a623df5" xsi:type='ttp:TTPType' version="1.1"> <ttp:Title>Phishing</ttp:Title> <ttp:Behavior> <ttp:Attack_Patterns> <ttp:Attack_Pattern capec_id="CAPEC-98"> <ttp:Description>Phishing</ttp:Description> </ttp:Attack_Pattern> </ttp:Attack_Patterns> </ttp:Behavior> </stix:TTP> <stix:TTP id="example:ttp-d1c612bc-146f-4b65-b7b0-9a54a14150a4" xsi:type='ttp:TTPType' version="1.1"> <ttp:Title>Poison Ivy Variant d1c6</ttp:Title> <ttp:Behavior> <ttp:Malware> <ttp:Malware_Instance id="example:malware-1621d4d2-b67d-11e3-ba9e-f01faf20d111"> <ttp:Type xsi:type="stixVocabs:MalwareTypeVocab-1.0">Remote Access Trojan</ttp:Type> <ttp:Name>Poison Ivy Variant d1c6</ttp:Name> </ttp:Malware_Instance> </ttp:Malware> </ttp:Behavior> </stix:TTP> </stix:TTPs> <stix:Threat_Actors> <stix:Threat_Actor id="example:threatactor-9a8a0d25-7636-429b-a99e-b2a73cd0f11f" xsi:type='ta:ThreatActorType' version="1.1"> <ta:Title>Adversary Bravo</ta:Title> <ta:Identity id="example:Identity-1621d4d4-b67d-11e3-9670-f01faf20d111"> <stixCommon:Name>Adversary Bravo</stixCommon:Name> </ta:Identity> <ta:Observed_TTPs> <ta:Observed_TTP> <stixCommon:Relationship>Leverages Attack Pattern</stixCommon:Relationship> <stixCommon:TTP idref="example:ttp-8ac90ff3-ecf8-4835-95b8-6aea6a623df5"/> </ta:Observed_TTP> <ta:Observed_TTP> <stixCommon:Relationship>Leverages Malware</stixCommon:Relationship> <stixCommon:TTP idref="example:ttp-d1c612bc-146f-4b65-b7b0-9a54a14150a4"/> </ta:Observed_TTP> </ta:Observed_TTPs> </stix:Threat_Actor> </stix:Threat_Actors>
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 stix_package = STIXPackage() ttp_phishing = TTP(title="Phishing") attack_pattern = AttackPattern() attack_pattern.capec_id = "CAPEC-98" attack_pattern.description = ("Phishing") ttp_phishing.behavior = Behavior() ttp_phishing.behavior.add_attack_pattern(attack_pattern) ttp_pivy = TTP(title="Poison Ivy Variant d1c6") malware_instance = MalwareInstance() malware_instance.add_name("Poison Ivy Variant d1c6") malware_instance.add_type("Remote Access Trojan") ttp_pivy.behavior = Behavior() ttp_pivy.behavior.add_malware_instance(malware_instance) ta_bravo = ThreatActor(title="Adversary Bravo") ta_bravo.identity = Identity(name="Adversary Bravo") related_ttp_phishing = RelatedTTP(TTP(idref=ttp_phishing.id_), relationship="Leverages Attack Pattern") ta_bravo.observed_ttps.append(related_ttp_phishing) related_ttp_pivy = RelatedTTP(TTP(idref=ttp_pivy.id_), relationship="Leverages Malware") ta_bravo.observed_ttps.append(related_ttp_pivy) stix_package.add_ttp(ttp_phishing) stix_package.add_ttp(ttp_pivy) stix_package.add_threat_actor(ta_bravo) print(stix_package.to_xml(encoding=None))
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 print("== MALWARE ==") for tactic in pkg.ttps: print("---") print("Title : " + tactic.title) if tactic.behavior.attack_patterns: for behave in tactic.behavior.attack_patterns: print("CAPEC: " + str(behave.capec_id)) print("Description: " + str(behave.description)) if tactic.behavior.malware_instances: for sample in tactic.behavior.malware_instances: print("Sample: " + str(sample.names)) print("Type: " + str(sample.types)) print("== ACTOR ==") for actor in pkg.threat_actors: for obs in actor.observed_ttps: print("RelatedTTP: " + str(pkg.find(obs.item.idref).title)) print("Relationship: " + str(obs.relationship)) print("Title: " + str(actor.title)) print("Name: " + str(actor.identity.name))
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This idiom can be composed with the C2 indicator idiom to represent both the C2 infrastructure itself (as here) and the set of indicators for that infrastructure. Simply replace the TTP in that idiom, which only has a title, with something similar to the TTP in this idiom that includes a structured description of the C2 range.