applied machine learning defeating modern malicious documents

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Evan Gaustad

Applied Machine Learning:Defeating Modern Malicious Documents

HT-W02

Sr. Manager CSIRTTarget Corporation

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Agenda

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Office Macro Use and Abuse

Malicious documents in attack lifecycle

Machine Learning for Malware Detection

Demo Project: Malicious Macro Bot

Conclusion

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Macro-enabled Microsoft Office Documents

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An office macro is code that automates tasks in office documents

Automatically fill out formsUpdate graphs and display dataMake web requestsPerform computations

Written in Visual Basic for Applications (VBA)

VBA Support built into MS Office

99.7% of documents used in attachment-based campaigns relied on social engineering and macros, rather than exploits.- Proofpoint1

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Attacker motivation for malicious office docs

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Barrier of entry is very low

Uses built in, cross-platform features“exploit” reliability is high

Can implement sandbox evasion

Easy to update to evade AV signatures

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Malicious Macro-enabled Office Documents

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Used by an attacker to gain code execution on the targeted system(s)

Common Attacker VBA Techniques:Download and execute malicious payloadDrop and execute embedded payloads or scriptsObfuscation to hide intentSandbox evasion techniquesPayload targeting

…

“98% of Office-targeted threats use macros”- Microsoft2

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwir-fnOifDRAhXr24MKHQ8MDIMQjRwIBw&url=http://www.filetypes.ru/pptm/&bvm=bv.146073913,d.amc&psig=AFQjCNGMABrg-hIE5lL2A4GZYoHItnH5hg&ust=1486078894194663

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwir-fnOifDRAhXr24MKHQ8MDIMQjRwIBw&url=http://www.filetypes.ru/pptm/&bvm=bv.146073913,d.amc&psig=AFQjCNGMABrg-hIE5lL2A4GZYoHItnH5hg&ust=1486078894194663

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Example: Maldocs in Attack Lifecycle

1) Phishing email with attachment

“Invoice Past Due”

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2) Victim opens file, allows macros to run


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3) Malicious macro executes

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4) Downloads / drops executables or powershell

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5) Install additional malware e.g. Pony, Hancitor, Vawtrak

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5) Install additional malware e.g. Pony, Hancitor, Vawtrak

6) Steal credentials, data, maintain persistence, command and control

VictimAttackerhttp://.../gate.php

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Detecting Malicious MacrosHow hard is it to create:

a malicious macro…that runs an executable…on victim’s machine…and evades AV?

Some easy to find tools:CrunchCode7

MacroShop8

Veil Framework9

Generate-Macro10

Criminals sell their own

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Detecting Malicious MacrosHow hard is it to create:

a malicious macro…that runs an executable…on victim’s machine…and evades AV?

Some easy to find tools:CrunchCode7

MacroShop8

Veil Framework9

Generate-Macro10

Criminals sell their own

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Really easy

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Detecting Malicious Macros

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Detecting Malicious Macros

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Why Machine Learning?

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Existing anti-virus and sandbox techniques can be subverted

Automates extracting insight from file samples

Can better generalize at identifying unknown variations

Reduces human analysis time

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Project Approach

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Goals:Triage: Determine whether a new Microsoft Office document contains a malicious or benign macroDetection: Provide useful detection when signature-based methods failThreat Intelligence: identify phishing campaigns

Guiding Principles:Supervised Machine Learning – ClassificationWell thought out featuresGeneralized and interpretable model output

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Applied Machine Learning Steps

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Benign Files

Malicious Files

Collect labeled data

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Benign Files

Malicious FilesFeature

Extraction

5.7 10 98 …1.2 23 15 …0.7 57 20 …

…

Collect labeled data Feature extraction

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“Feature Engineering”

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DOCUMENT #1…BHJASD = Chr(102 + 8)Set uHhdBhd = CreateObject("" & "W" & "" & "or" & "d." & "Applicatio" & BHJASD)uHhdBhd.Documents.Open(FFFNNNF)Module1.Tyryka (2)HYUASGD = Module1.Girow(WOIEW)Module1.Tyryka (3)uHhdBhd.QuitSet uHhdBhd = NothingEnd SubPublic Function Girow(qqa As String)Dim jjz As Variantjjz = Shell(qqa, 0)…

DOCUMENT #2…'#############################'# Code to Add Total Value Formula #'##############################

'Go to the top of the Price columnRange("H10").Select

'Find the bottom value - there are no values in the Non Stock Items

Selection.End(xlDown).Select'Check to see if still in the order form range - if not there were no Standard Items Selected

If ActiveCell.Row > 1000 Then GoToTidyUp…

Which one is malicious?

Why?

How would you measure that?

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“Feature Engineering”

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DOCUMENT #2…'#############################'# Code to Add Total Value Formula #'#############################





Feature Doc1 Doc2# Lines of Code 74 584# Comments 8 161# Functions 9 14# Shell Instructions 1 0

Entropy 4.3 3.8

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Feature Engineering

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Feature Engineering

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Benign Files


Extraction

5.7 10 98 …1.2 23 15 …0.7 57 20 …

…Classification

Model

Collect labeled data Feature extraction Train and Testmodel

Classification Models

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Choose and Test Model

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DOCUMENT #2…'#############################'# Code to Add Total Value Formula #'##############################





Feature Doc1 Doc2# Lines of Code 74 584# Comments 8 161# Functions 9 14# Shell Instructions 1 0

Entropy 4.3 3.8

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Simple Decision Tree Model

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entropy <= 4.27samples = 88

samples = 47class = benign

# comments <= 39.0samples = 41


samples = 47class = malicious

True False

True False

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Simple Decision Tree Model

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entropy <= 4.27samples = 88


# comments <= 39.0samples = 41


samples = 47class = malicious

True False

True False

Doc #1

Feature Doc1 Doc2Entropy 4.3 3.8# Comments 8 161

Doc #2

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Benign Files


Extraction

5.7 10 98 …1.2 23 15 …0.7 57 20 …

…Classification

Model

Collect labeled data Feature extraction Train and Testmodel

Classification Model

Deploy Model

NewFiles

“Benign”“Malicious”

Classification Models

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Malicious Macro Bot Project

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Model factored in over 20,000 samples

Analyzed over 121,000 samples from 7 months of VirusTotal samples

Over a thousand featuresVBA built-in language semantics for base language e.g. Shell, Dim, If, …Code heuristics e.g. LOC, # functions, entropy, …

Use Random Forest Classifier Fits many decision trees on many subsets of the datasetPicks best decision tree combinations“Ensemble”

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Demo: Malicious Macro Bot Project

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Demonstrate classification

Gaining insight from machine learning features

Identifying phishing campaigns through featureprints

Search and visualize in Elasticsearch / Kibana

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Conclusion

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Project Uses:Threat Intelligence: Identify new phishing campaignsDetection: Fill traditional detection gapsIncident Response: Rapid triage of office documents

Prevention would be best

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Thank You!

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https://github.com/egaus/MaliciousMacroBot

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References

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[1] Proofpoint “Human Factor Report”, 2016. https://www.proofpoint.com/sites/default/files/human-factor-report-2016.pdf[2] Microsoft, “New feature in Office 2016 can block macros and help prevent infection”, Mar 22, 2016. https://blogs.technet.microsoft.com/mmpc/2016/03/22/new-feature-in-office-2016-can-block-macros-and-help-prevent-infection/[3] Proofpoint, “The Cybercrime Economics of Malicious Macros”, 2016. https://www.proofpoint.com/sites/default/files/documents/bnt_download/pp-macroeconomics-rr.pdf[4] Ankit Anubhav, Dileep Kumar Jallepalli. “Hancitor (aka Chanitor) Observed Using Multiple Attack Approaches”. FireEye. Sept 23, 2016. https://www.fireeye.com/blog/threat-research/2016/09/hancitor_aka_chanit.html[5] PonyUp: Tracing Pony’s Threat Cycle and Multi-Stage Infection Chain. Damballa. Aug. 2015. https://www.damballa.com/wp-content/uploads/2015/08/Damballa_PonyUp.pdf[6] New Hancitor: Pimp my Downloader. Minerva Labs Research Team. Aug 19, 2016. http://www.minerva-labs.com/post/new-hancitor-pimp-my-downloader[7] CrunchCode http://www.crunchcode.de/en/index.html[8] MacroShop https://github.com/khr0x40sh/MacroShop[9] Veil Evasion Framework https://github.com/Veil-Framework/Veil-Evasion[10] Generate-Macro https://github.com/enigma0x3/Generate-Macro[11] SciKit Learn Algorithm Cheat Sheet. http://scikit-learn.org/stable/tutorial/machine_learning_map/

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Thank You!

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Questions?

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Offline Demo

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Identifying Phishing Campaigns

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applied machine learning defeating modern malicious documents

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