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Introduction to Malware Analysis

This document provides an overview of malware analysis, including both static and dynamic analysis techniques. Static analysis involves examining a file's code and components without executing it, such as identifying file types, checking hashes, and viewing strings. Dynamic analysis involves executing the malware in a controlled environment and monitoring its behavior and any system changes. Dynamic analysis tools discussed include Process Explorer, Process Monitor, and Autoruns to track malware processes, files accessed, and persistence mechanisms. Both static and dynamic analysis are needed to fully understand malware behavior.

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Introduction to Malware Analysis
Disclaimer • This stuff requires the analyst to dive extremely deep into technical details • This quick talk will attempt to give you a 1000 foot view of malware analysis • I put a careful distinction between Malware Analysis and Reverse Engineering
Malware Analysis Overview • Static Analysis: involves analyzing the code without actually running the code – File identification, header information, strings, etc. – Disassembler – IDA Pro • Dynamic Analysis: involves executing the code in a controlled manner and monitoring system changes – Sysinternals, memory forencis, etc. – Debuggers – Immunity Debugger OllyDbg
Coding Terms • Malware authors with code in High Level Programming Language: C/C++
Static Analysis: File Identification • Linux “file” utility • Python-magic module
Static Analysis: MD5 Hash • Linux “md5sum” utility: md5sum <fileName> • Python hashlib module:
Static Analysis: Strings • Can be a quick way to gain intelligence from the file: – Domains, Ips, URLs, Function names, hardcoded information
Static Analysis: Packers • Packers are used to obfuscate the code which leads to: Changes the file signature (MD5 Hash) – Obfuscates the file strings, and code – Compress file size (sometimes) • Packed code can be identified by: – Examining the PE sections, and Imports: If a PE file only has LoadLibrary/GetProcAddress normally packed – Strings: UPX0, UPX1, aspack, adata, NSP0, NSP1, WinRAR SFX, PEC2, PECompact2, Themida, Orean.sys, NTkrnl, Secure Suite • Tools like (PEiD, LordPE, and Python peutils module)
Static Analysis: Packers • Unpacked vs. Packed Strings:
Data Encoding • Malware uses encoding for a number of reasons, some are to disguise internal workings, hide C2 information, and data exfil – Some simple encoding algorithms are: – Character Substitution – XOR – uses a static key to XOR with the original value – Base64 – Can use default or custom character set – Default Base64 character set: A-Z, a-z, 0-9, +, / • We will examine two common data encoding techniques used in Malware XOR and Base64
Data Encoding: XOR • Strings are often required to be stored in a program in order to pass it as a parameter to a function • XOR once = encoded • XOR again with same key = plaintext
Data Encoding: Base64 • Storing base64 strings as HTML comments is how the APT group “Comment Crew” got their name. This technique is still leveraged today in malware • Base64 is a common encoding scheme because it is very easy to decode
Static Analysis: PE File Format • PE data structure contains all the information required for the Windows OS loader to manage executable code. .text – instructions the CPU executes – .rdata – Imports and Exports – .data – Global data – .rsrc – Resources (icons, images, strings, etc.) • Useful information in PE header: Imports and Exports – Gives an idea to malware functionality – Compilation Time, Language Settings, and strings – Section Names – Packed code can have non-standard section names • Tools to analyze PE header: pescanner.py, CFF Explorer, python pefile, Resource Hacker, Dependency Walker, LordPE, etc.
Windows API Calls: • When performing advanced static or dynamic analysis it’s important to have a good understanding of Windows API calls • By looking at the imported functions within the PE header you can see which Windows API functions the PE file wants to utilize • By recognizing API calls you can quickly get an idea of malware’s functionality by analyzing strings output, and during advanced static analysis using a disassembler • An excellent resource for Windows API calls is MSDN. Google search “API_Function MSDN”
Windows API: MSDN Example • The Parameters modify how the function will be used on the system. • The return type is what the function will return after it is called in a program
Windows API: Disassembly • Parameters are pushed to the stack in Last In First Out(LIFO) order, which is why they are in reverse order in the disassembly
Wake Up  • Okay, that was likely starting to bore some people – SORRY • Let’s move to Dynamic analysis which is more flashy
Getting Infected • Double clicking the executable doesn’t always work – Sometimes you need to register the malware as a service or load it as a DLL (regsvr32.exe and rundll32.exe ) • Install the malware as a service – Interact with the system like a normal user The malware may be waiting for a certain application to open to inject code into it (Ex: Internet Explorer) – It could require a CLI argument : One sample required <filename> /install in order to actually run the malware – Static analysis is normally required to determine CLI switches
SysInternals Tool Suite • If I could pick just one tool, id pick the 50+ in the Sysinternals tool suite  • Tools put out by Mark Russinovich – now works for Microsoft • Process Explorer, Process Monitor, Autoruns, etc.
Process Explorer
Process Monitor • Very verbose tool that generates a lot of events • Filtering is required to make sense of the data
Process Monitor Cont. • Press Ctrl+L to bring up the filtering dialog box – Quick filters are: Operation is WriteFile – Category is Write
Malware Persistence - Autoruns • Really is the key to identify malware – how does it gain persistence? • Autoruns can help enumerate persistence mechanisms:
Monitoring Network Activity • Some interesting network indicators of malware are: – SYNs out to an IP or domain – UDP traffic to IP or domain – HTTP GET/POST requests – DNS Queries – Connection attempt times are important. Every 1 min, 30mins, etc.
Automation? Sandboxes • So far the basic dynamic analysis we have talked about can be automated • Sandboxes are a good tool in any malware analyst toolbox – they have Pro’s and Con’s: – Pros: Speeds up analysis, fast, saves time – Cons: Misses details, can be fooled • Sandboxes can be open source or commercial: – Really good free option is Cuckoo sandbox: • Install Tutorial: http://www.primalsecurity.net/im-cuckoo-for-malware- with-a-spice-of-reverse-engineering/
Summary • Malware analysis requires both static and dynamic analysis techniques to accurately enumerate indicators of compromise • As with any automated tool an analyst will need to be able to validate findings manually