Untangling the code An overview of techniques to reverse engineer malicious software Prashant Gupta Security Architect, McAfee Inc. June 3, 2013 McAfee Confidential — Internal Use Only
Abstract Reverse engineering and analysis of binary code has been seen as a black art that requires immense commitment, large degree of experience and intuition to be fruitful. This may have been true a couple of decades ago but with the recent focus on reverse code engineering by security vendors and prolific malicious actors alike this field has progressed significantly. In this talk I will present some of the techniques employed during reversing of unknown binaries when vetting them for malicious traits. The talk would also cover how program analysis can help identify possibly suspicious traits in code and how reverse engineering and program analysis techniques used for code are also relevant for identifying potentially suspicious data when analysing document formats. 2 June 3, 2013
Reverse Code Engineering: What? Scanners/Fingerprinting Decoders/Decryptors Code Unpackers Environment Behaviour Analysers Interactions Code reversers … … Better Understanding 3 June 3, 2013
Reverse Code Engineering: Why? • Improve understanding where source code is not available • Audit, review or forensic investigation of software systems • Identifying intellectual property licensing breach • Malware research & defence 4 June 3, 2013
Malware prevalence Historically…. 54M+ 100000000 10000000 1000000 164,000 56,342 100000 8,069 10000 357 1000 100 10 1 1990 1995 2000 2005 2010 5 June 3, 2013
Malware prevalence: Why? Packer Junk-Code Chaining Dynamic Anti- Functionality Emulation Extension Destroy Compression structures Anti- Encryption Disassembly Malware New attack Virtualization vectors Code 6 June 3, 2013
Reversing Code: Static Analysis • Automated Signature Search – Text search – Binary signatures – Known blobs, tables and data structure search • Decoding/decrypting code and payload - Identifying and decoding encoded payloads - From XORs to Purpose Built Custom algorithms (e.g. usage pseudo-random) • Code Block identification - Compiler and Library recognition - Fingerprinting known obfuscation techniques - Dealing with compiler optimizations - Semantic code similarity identification 7 June 3, 2013
Reversing Code: Static Analysis • Decompiling - Identifying boiler-plate code - Make complex code easier to understand (e.g. algorithms) - Many issues, after so many years still in it’s infancy. • Packer identification and Un-Packing - Identify if binary is a setup, built using a binder/packer/cryptor - Unpack using custom, generic or standard algorithms. • Artefact extraction and logging - Structural anomalies - Known code patterns (e.g. peculiar function chaining) - Junk-code or no-op code search 8 June 3, 2013
Reversing Code: Dynamic Analysis • Virtualization/Sandboxing and Debugging - Control malware exposure and it’s ability to leave irreversible changes. - Debugging to guide execution flows (bypass exceptions) - Providing stimulus to force malware to exhibit behaviour - Active and passive analysis platforms. • Behaviour logging - Automated behaviour trace logging - Identify communication mechanism - Identify persistence mechanism • Post/Part execution memory dumps - Generate memory dumps for detailed static analysis - In cases where unpacking is not possible/feasible - In cases where in-memory data structures need analysis - Runtime unpacking 9 June 3, 2013
Reversing Code: Machine Correlation • Correlation for high level behaviour inference - correlation of artefacts extracted from automated analysis • Automated Classification - Behavioural trait association - Static code relationships - Malware family 10 June 3, 2013
Reversing Code: Manual Investigation • Separating the wheat from the chaff – Identifying suspicious code – Evaluating known patterns and guiding analysis process – Making decisions where automation could only provide approximations. • Optimizing program code analysis - Correlating artefacts from static and behavioural analysis - Building new algorithms - Fixing problems faced by automation (exceptions, resource constraints, etc.) - Manual unpacking/decoding • Heuristic development - Adding new feature extraction methods - New correlation policies - New subsystem development for analysis and detection improvements 11 June 3, 2013
Reverse Engineering documents Binary Code Binary Documents Analysis Not human readable Yes Yes RE tools and environment Multitude of Many execution Documents are Heuristic analysis environments environments including generally platform systems can be shared VMs agnostic. when analysing artefact correlation. Can exploit Yes, but not always Yes, generally in Dynamic analysis vulnerabilities needed. document editor/reader techniques can be used but sometimes in OS Internal formats can be Yes Yes Detecting encoded obfuscated payloads. Identifying presence of obfuscation. Executable Code Yes No Signature searches and payload analysis techniques. 12 June 3, 2013
13 100 An example technique… 10 20 30 40 50 60 70 80 90 0 100 38400 76700 115000 153300 191600 229900 268200 306500 344800 explorer.exe 383100 421400 459700 498000 536300 574600 612900 651200 689500 727800 766100 804400 842700 881000 919300 957600 June 3, 2013 995900 100 10 20 30 40 50 60 70 80 90 0 100 14500 28900 43300 57700 upx compressed explorer.exe 72100 86500 100900 115300 129700 144100 158500 172900 187300 201700 216100 230500 244900 259300 273700 288100 302500 316900 331300 345700 360100 374500
100 10 20 30 40 50 60 70 80 90 0 14 An example technique… 100 157900 315700 473500 631300 document with hidden executable 789100 946900 1104700 1262500 1420300 1578100 1735900 1893700 2051500 2209300 2367100 2524900 2682700 2840500 2998300 3156100 3313900 3471700 3629500 3787300 3945100 4102900 June 3, 2013 4260700 4418500 4576300 100 4734100 10 20 30 40 50 60 70 80 90 0 100 157900 315700 473500 631300 789100 946900 1104700 1262500 1420300 1578100 1735900 1893700 document 2051500 2209300 2367100 2524900 2682700 2840500 2998300 3156100 3313900 3471700 3629500 3787300 3945100 4102900 4260700 4418500 4576300 4734100
Open source toolsets SysAnalyzer - Automated malcode analysis system (not a sandbox!) Malcode Analyst Pack - suite of tools useful for malcode analysts VirtualBox - x86 and AMD64/Intel64 virtualization product BeaEngine - disassembler library x86 x86-64 (IA32 and Intel64) Libemu - x86 shellcode emulation 15 June 3, 2013
Databases/Tools RE-Google IDA plugin Queries Google Code for information about the functions contained in a disassembled binary ClamAV Open source (GPL) antivirus engine Malware lookup services VirusTotal, The Malware Hash Registry ThreatExpert, McAfee SiteAdvisor Utilities and Assessment Tools McAfee Free Tools, Collaborative RCE Tool Library 16 June 3, 2013
Extensible analysis frameworks Cuckoo Sandbox - Modular malware analysis system Zero Wine Malware Analysis Tool - Research project to dynamically analyse the behaviour of malware Malheur - Automatic analysis of malware behaviour Radare - Open source tools to disasm, debug, analyse, manipulate binary files 17 June 3, 2013
Prashant Gupta Security Architect, McAfee Inc. @PrashantGupta
References IMPORTANT: These are 3 rd party websites so please review what you download for malware/suspicious content before use. 1. Cuckoo Sandbox: http://www.cuckoosandbox.org/ 2. Zero Wine Malware Analysis Tool: http://zerowine.sourceforge.net/ 3. Malheur: http://www.mlsec.org/malheur/ 4. Radare: http://www.radare.org/ 5. Interactive Disassembler Pro: http://www.hex-rays.com/ 6. REGoogle: http://regoogle.carnivore.it/ 7. ClamAV: http://www.clamav.net/ 8. SysAnalyzer: https://github.com/dzzie/SysAnalyzer 9. Example technique from - Detecting exploits in electronic objects, Alexander Shipp: http://www.google.com/patents/US20080134333 19 June 3, 2013
References IMPORTANT: These are 3 rd party websites so please review what you download for malware/suspicious content before use. 10. Malcode Analyst Pack: https://github.com/dzzie/MAP 11. VirusTotal: http://www.virustotal.com/ 12. The Malware Hash Registry: http://www.team-cymru.org/Services/MHR/ 13. ThreatExpert: http://www.threatexpert.com 14. McAfee SiteAdvisor: http://www.siteadvisor.com/ 15. McAfee Free Tools: http://www.mcafee.com/us/downloads/free-tools/ 16. Collaborative RCE Tool Library: http://www.woodmann.com/collaborative/tools/index.php/Category:RCE_To ols 17. McAfee Threats Report Q4 2012: http://www.mcafee.com/uk/resources/reports/rp-quarterly-threat-q4- 2012.pdf 20 June 3, 2013
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