Window-based rarity determination using probabilistic suffix trees for network security analysis

• US 10,560,468 B2
• Filed: 07/20/2018
• Issued: 02/11/2020
• Est. Priority Date: 08/31/2015
• Status: Active Grant

• Current Assignee: Splunk Inc.
• Original Assignee: Splunk Inc.
• Inventors: Muddu, Sudhakar, Tryfonas, Christos, Iliofotou, Marios
• Primary Examiner(s): Hirl, Joseph P
• Assistant Examiner(s): Gyorfi, Thomas A
• Application Number:
  US16/041,637
• Publication Number:
  US 20180351981A1
• Time in Patent Office: 571 Days
• CPC Class Codes: G06F 16/24578 using ranking
• CPC Class Codes: G06F 16/254 Extract, transform and load [ETL] procedures, e.g. ETL data flows in data warehouses
• CPC Class Codes: G06F 16/285 Clustering or classification
• CPC Class Codes: G06F 16/444 Spatial browsing, e.g. 2D maps, 3D or virtual spaces
• CPC Class Codes: G06F 16/9024 Graphs; Linked lists G06F16/9027 takes precedence
• CPC Class Codes: G06F 3/0482 Interaction with lists of selectable items, e.g. menus
• CPC Class Codes: G06F 3/0484 for the control of specific functions or operations, e.g. selecting or manipulating an object, an image or a displayed text element, setting a parameter value or selecting a range
• CPC Class Codes: G06F 3/04842 Selection of displayed objects or displayed text elements G06F3/0482 takes precedence
• CPC Class Codes: G06F 3/04847 Interaction techniques to control parameter settings, e.g. interaction with sliders or dials
• CPC Class Codes: G06F 40/134 Hyperlinking
• CPC Class Codes: G06N 20/00 Machine learning
• CPC Class Codes: G06N 20/20 Ensemble learning
• CPC Class Codes: G06N 5/022 Knowledge engineering; Knowledge acquisition
• CPC Class Codes: G06N 5/04 Inference or reasoning models
• CPC Class Codes: G06N 7/01 Probabilistic graphical models, e.g. probabilistic networks
• CPC Class Codes: G06V 10/225 based on a marking or identifier characterising the area
• CPC Class Codes: H04L 2463/121 Timestamp cryptographic mechanisms or cryptographic arrangements involving time stamps H04L9/3297
• CPC Class Codes: H04L 41/0893 Assignment of logical groups to network elements
• CPC Class Codes: H04L 41/145 involving simulating, designing, planning or modelling of a network
• CPC Class Codes: H04L 41/22 comprising specially adapted graphical user interfaces [GUI]
• CPC Class Codes: H04L 43/00 : Arrangements for monitoring or testing data switching networks
• CPC Class Codes: H04L 43/045 : for graphical visualisation of monitoring data
• CPC Class Codes: H04L 43/062 : related to network traffic
• CPC Class Codes: H04L 43/08 : Monitoring or testing based on specific metrics, e.g. QoS, energy consumption or environmental parameters
• CPC Class Codes: H04L 63/06 : for supporting key management in a packet data network cryptographic mechanisms or cryptographic arrangements for key management H04L9/08
• CPC Class Codes: H04L 63/1408 : by monitoring network traffic monitoring network traffic per se H04L43/00
• CPC Class Codes: H04L 63/1416 : Event detection, e.g. attack signature detection
• CPC Class Codes: H04L 63/1425 : Traffic logging, e.g. anomaly detection
• CPC Class Codes: H04L 63/1433 : Vulnerability analysis
• CPC Class Codes: H04L 63/1441 : Countermeasures against malicious traffic countermeasures against attacks on cryptographic mechanisms H04L9/002
• CPC Class Codes: H04L 63/20 : for managing network security; network security policies in general filtering policies H04L63/0227
• CPC Class Codes: H05K 999/99 : dummy group

Abstract

A security platform employs a variety techniques and mechanisms to detect security related anomalies and threats in a computer network environment. The security platform is “big data” driven and employs machine learning to perform security analytics. The security platform performs user/entity behavioral analytics (UEBA) to detect the security related anomalies and threats, regardless of whether such anomalies/threats were previously known. The security platform can include both real-time and batch paths/modes for detecting anomalies and threats. By visually presenting analytical results scored with risk ratings and supporting evidence, the security platform enables network security administrators to respond to a detected anomaly or threat, and to take action promptly.

Claims

1. A method comprising:

receiving a sequence of event feature sets corresponding to a sequence of events, wherein the event feature sets are derived from raw event machine data recorded in a computer network;

measuring an anomaly count within a target event window by processing the sequence of event feature sets through an event sequence prediction model to increase the anomaly count when the event sequence prediction model identifies an event feature set within the target event window as corresponding to an anomalous event, wherein the event sequence prediction model includes a probabilistic suffix tree (PST) based machine learning model;

comparing a rarity score for the target event window against an established baseline distribution to determine a probability of encountering the event window with the rarity score; and

upon determining that the probability of encountering the event window is below a threshold, identifying the target event window as containing a suspicious series of events by determining whether the anomaly count deviates from a baseline by a specified criterion; and

generating a computer security threat indicator or a computer security anomaly indicator based on the identification of the suspicious series of events.

2. The method of claim 1, further comprising:

training the event sequence prediction model based on a number of past sequence of event feature sets such that the event sequence prediction model, when deployed and given a historical event feature set sequence, is to generate a probability of encountering a particular event as the next event.

3. The method of claim 1, further comprising:

establishing, for a particular entity, an entity-specific baseline distribution of anomaly counts based on using the event sequence prediction model to calculate rarity scores for a number of baseline profiling windows of events.

4. The method of claim 1, further comprising:

establishing, for a particular entity, an entity-specific baseline distribution of anomaly counts based on using the event sequence prediction model to calculate rarity scores for a number of baseline profiling windows of events,

wherein establishing an entity-specific baseline distribution of anomaly counts is further based on using the event sequence prediction model to generate a probability of encountering a window with a particular rarity score, given a history of previous rarity scores.

5. The method of claim 1, further comprising:

establishing, for a particular entity, an entity-specific baseline distribution of anomaly counts based on using the event sequence prediction model to calculate rarity scores for a number of baseline profiling windows of events,

wherein a rarity score among the rarity scores for the baseline profiling windows is calculated based on (a) a number of predictions that are below a threshold inside the baseline profiling window; and

(b) a length of the baseline profiling window.

6. The method of claim 1, further comprising:

storing target event windows that are identified as containing a suspicious series of events in a rare window database.

7. The method of claim 1, wherein the rarity score for the target event window is calculated based on (a) a number of event feature sets within the target event window identified as corresponding to an anomalous event;

and (b) a length of the target event window.

8. The method of claim 1, wherein the target event window is a moving event window of a constant number of most recent, consecutive event feature sets in the sequence of event feature sets.

9. The method of claim 1, further comprising determining when the event sequence prediction model has sufficient training to be deployed;

wherein said determining when the event sequence prediction model has sufficient training includes measuring how many events have been used to train the event sequence prediction model.

10. The method of claim 1, further comprising determining when the event sequence prediction model has sufficient training to be deployed;

wherein said determining when the event sequence prediction model has sufficient training includes measuring how long the event sequence prediction model has been in training.

11. The method of claim 1, further comprising determining when the event sequence prediction model has sufficient training to be deployed;

wherein said determining when the event sequence prediction model has sufficient training includes determining whether numeric values in a model state representative of the event sequence prediction model are converging.

12. The method of claim 1, further comprising determining when the event sequence prediction model has sufficient training to be deployed;

wherein said determining when the event sequence prediction model has sufficient training includes determining whether recent versions of the event sequence prediction model produce scores that deviate within a given threshold from each other when applied with same inputs.

13. The method of claim 1, wherein identifying the target event window as containing a suspicious series of events includes:

scoring an event feature set based on the event sequence prediction model to determine whether an event corresponding to the event feature is an anomaly event; and

updating the anomaly count based on whether the event is an anomaly event.

14. The method of claim 1, wherein identifying the target event window as containing a suspicious series of events includes maintaining the anomaly count within a moving event window by incrementing the anomaly count whenever a most-recent event feature set as applied to the event sequence prediction model produces a score that is beyond a preset threshold;

the method further comprising designating a most-recent event corresponding to the most-recent event feature set as an anomalous event when the score is beyond the preset threshold.

15. The method of claim 1, wherein identifying the target event window as containing a suspicious series of events includes maintaining the anomaly count within a moving event window by decrementing the anomaly count whenever an anomalous event designated by the event sequence prediction model falls outside of the moving event window.

16. The method of claim 1, further comprising:

comparing a similarity of the target event window to past rare windows based on a combination of different similarity metrics.

17. The method of claim 1, further comprising expanding the suspicious series of events by adding an additional event corresponding to an additional feature set into the suspicious series, in response to identifying the target event window as containing the suspicious series.

18. The method of claim 1, further comprising expanding the suspicious series of events;

and wherein expanding the suspicious series of events includes holding a starting event of the suspicious series of events while the suspicious series of events expands to include an additional event and its corresponding event feature set that is subsequently processed by the event sequence prediction model.

19. The method of claim 1, further comprising:

expanding the suspicious series of events; and

updating the anomaly count as the suspicious series of events expands; and

stopping said expanding when the anomaly count stops increasing above a preset threshold.

20. The method of claim 1, further comprising expanding the suspicious series of events until the suspicious series of events expands beyond a threshold percentage.

21. The method of claim 1, further comprising creating an event window signature from event feature sets corresponding to the suspicious series of events.

22. The method of claim 1, further comprising:

expanding the suspicious series of events; and

creating an event window signature after the suspicious series of events stops expanding.

23. The method of claim 1, further comprising creating an event window signature by building an array comprised of computed scores from the event sequence prediction model for each event feature set corresponding to each event in the suspicious series of events.

24. The method of claim 1, further comprising:

creating an event window signature from event feature sets corresponding to the suspicious series of events;

computing another event window signature from another event window; and

determining whether the other event window is suspicious by comparing the other event window signature against the event window signature of the suspicious series of events.

25. The method of claim 1, further comprising:

computing an event window signature of the target event window; and

determining whether the target event window corresponds to a computer security-related threat based on whether the event window signature corresponds to an existing signature in an event window signature database.

26. The method of claim 1, further comprising:

computing a current event window signature of a most-recent event window; and

determining whether the most-recent event window corresponds to a real-time computer security threat based on whether the current event window signature corresponds to an existing signature in an event window signature database.

27. The method of claim 1, further comprising:

computing an event window signature of the target event window; and

determining whether the target event window corresponds to a computer security threat when the event window signature fails to match an existing signature in an event window signature database within a threshold difference.

28. The method of claim 1, wherein the events include timestamped machine data events.

29. A system comprising:

a memory storing computer-executable instructions; and

a processor configured by the computer-executable instructions to;

receive a sequence of event feature sets corresponding to a sequence of events, wherein the event feature sets are derived from raw event machine data recorded in a computer network;

measure an anomaly count within a target event window by processing the sequence of event feature sets through an event sequence prediction model to increase the anomaly count when the event sequence prediction model identifies an event feature set within the target event window as corresponding to an anomalous event, wherein the event sequence prediction model includes a probabilistic suffix tree (PST) based machine learning model;

compare a rarity score for the target event window against an established baseline distribution to determine a probability of encountering such event window with the rarity score; and

upon determining that the probability of encountering such event window is below a threshold, identify the target event window as containing a suspicious series of events by determining whether the anomaly count deviates from a baseline by a specified criterion; and

generate a computer security threat indicator or a computer security anomaly indicator based on the identification of the suspicious series of events.

30. A non-transitory machine readable medium storing instructions, execution of which by at least one processor in a computer system causes the computer system to:

receive a sequence of event feature sets corresponding to a sequence of events, wherein the event feature sets are derived from raw event machine data recorded in a computer network;

measure an anomaly count within a target event window by processing the sequence of event feature sets through an event sequence prediction model to increase the anomaly count when the event sequence prediction model identifies an event feature set within the target event window as corresponding to an anomalous event, wherein the event sequence prediction model includes a probabilistic suffix tree (PST) based machine learning model;

compare a rarity score for the target event window against an established baseline distribution to determine a probability of encountering such event window with the rarity score; and

upon determining that the probability of encountering such event window is below a threshold, identify the target event window as containing a suspicious series of events by determining whether the anomaly count deviates from a baseline by a specified criterion; and

generate a computer security threat indicator or a computer security anomaly indicator based on the identification of the suspicious series of events.