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[email protected] Malware Sandbox Emulation in Python

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• Master degree of CSIE, NTUST • Security Researcher - chrO.ot, TDOHacker • Speaker - BlackHat, DEFCON, VXCON - HITCON, SITCON, iThome >_cat ./Bio

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1. The challenges of Anti-Virus techniques 2. The implementation of WinAPI CreateProcess() 3. Build our own emulator for exe file (PE) - CPU? and emulate thread via Unicorn in Python - Deal with exe file mapping, IAT, EAT in our sandbox - Challenges of Malware Sandbox, and solution 4. Recap >_cat ./intro

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[email protected] The challenges of Anti-Virus techniques

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• Trend Anti-Virus products verify files in the technique named Malware Signature Detection • Anti-Virus products store all virus signatures in the cloud database • The most famous rule of malware signature is YARA >_Anti-Virus AntiVirus File System avideo.scr finance.docx malware.exe

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>_YARA-Rule rule silent_banker : banker { meta: description = "This is just an example" thread_level = 3 in_the_wild = true strings: $a = {6A 40 68 00 30 00 00 6A 14 8D 91} $b = {8D 4D B0 2B C1 83 C0 27 99 6A 4E 59 F7 F9} $c = "UVODFRYSIHLNWPEJXQZAKCBGMT" condition: $a or $b or $c } virustotal.github.io/yara

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With the improvement in malware technology, more and more malware source codes are released. A large number of malware variants have been developed in the wild. ┐(´∀｀)┌ This makes Anti-Virus products hard to detect all malicious in Malware-Signature-Detection Technique. >_Challenge? AntiVirus File System ma1ware.docx malware.exe m4lW4.re.scr

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What ...? Only Detect via Signature?

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>_Solution?

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>_Solution?

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>_from AV to RCE landave.io/2018/06/f-secure-anti-virus-remote-code-execution-via-solid-rar-unpacking

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A Cool Idea: Building a malware sandbox?

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>_Cuckoo? cuckoosandbox.org

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>_Cuckoo? cuckoosandbox.org

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A Cool Idea: Building a malware emulator?

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>_AV = more RCE? googleprojectzero.blogspot.com/2015/06/analysis-and-exploitation-of-eset.html

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>_Sandbox? •Cuckoo-like Sandbox •Emulator-like Sandbox •VM-like Sandbox

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>_Sandbox? •Cuckoo-like Sandbox •Emulator-like Sandbox •VM-like Sandbox

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The Final Goal ⚑ Get all the behavior of malware files without execution

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[email protected] General Compiler

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General Compiler Source.cpp Object Files Main.exe Compiler Assembly Codes Assembler Linker

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>_cat msgbox.c #include int main() { MessageBoxA( 0, "hi there.", "info", 0 ); return 0; }

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based on x86 Calling Convention #include int main() { MessageBoxA( 0, "hi there.", "info", 0 ); return 0; } push 0 push "info" push "hi there." push 0 call MessageBoxA xor eax, eax ret en.wikipedia.org/wiki/X86_calling_conventions

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>_Compiler xor eax, eax ret push 0 push "info" push "hi there." push 0 call MessageBoxA 0xdead: "info" 0xbeef: "hi there." .rdata section 0xcafe: 0x7630EA99 .idata section (Import Address Table)

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xor eax, eax ret push 0 push offset "info" push offset "hi there." push 0 call MessageBoxA 0xdead: "info" 0xbeef: "hi there." .rdata section 0xcafe: 0x7630EA99 .idata section (Import Address Table) >_Compiler

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xor eax, eax ret push 0 push 0x40dead push 0x40beef push 0 call ds:0x40cafe 0xdead: "info" 0xbeef: "hi there." .rdata section 0xcafe: 0x7630EA99 .idata section (Import Address Table) >_Compiler

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push 0 ; 6A 00 push 0x40dead ; 68 AD DE 40 00 push 0x40beef ; 68 EF BE 40 00 push 0 ; 6A 00 call ds:0x40cafe ; FF 15 FE CA 00 00 xor eax, eax ; 33 C0 ret ; C3 >_Assembler

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Main.exe .text Section 6A 00 68 AD DE 40 00 68 EF BE 40 00 6A 00 FF 15 FE CA 40 00 33 C0 C3 0xdead: "info" 0xbeef: "hi there." 0xcafe: 0x7630EA99 .rdata Section .idata Section

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[email protected] The Implementation of WinAPI CreateProcess()

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3) create first thread of this process, point register eax to AddressOfEntry, point ebx+8 (TIB base + 8) to image base, and point eip to ntdll!LdrInitializeThunk Process >_Process? Kernel (ring0) Application (ring3) 1) create process via CreateProcess() 2) mapping file into memory iexplorer.exe .data section .text section AddressOfEntry ntdll.dll kernel32.dll ...

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>_Process? Process iexplorer.exe ntdll.dll kernel32.dll ... Call Stack -------------- _LdrpSnapModule _LdrpMapAndSnapDependency _LdrpMapDllWithSectionHandle _LdrpLoadKnownDll _LdrpFindOrPrepareLoadingModule _LdrpLoadDllInternal _LdrpLoadDll _LdrLoadDll _LdrpInitializeProcess __LdrpInitialize _LdrInitializeThunk fix import address table, fix export directory, apply relocation, etc .text section ntdll!LdrInitializeThunk LdrMapAndSnapDependency: fix import address table for every loaded dll image

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>_ntdll!LdrpSnapModule

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>_Process? ntdll!LdrInitializeThunk [email protected] Process iexplorer.exe .text section ntdll.dll kernel32.dll ... ntdll!RtlUserThreadStart note: RtlUserThreadStart is entrypoint of every thread. We can hijack thread via write shellcode address into global variable'LdrDelegatedRtlUserThreadStart'.

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>_Qick Recap 1. Once a process creates, kernel maps each section into memory in the expected addresses 2. Next, kernel creates a new thread for this process. This thread will call ntdll!LdrInitializeThunk to repair Import Address Table (IAT), Export Address Table (EAT) and Relocation 3. Finally, thread enter func@AddressOfEntry

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[email protected] Build our own emulator for *.exe file

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>_for Emulator? 1. File Mapping - It's essential for codes to fetch information from each other section (e.g., [email protected] read [email protected]) 2. Repair IAT, Relocation - Repairing Import Address Table for malware to call WinAPI at correct address; In an emulator, it's easy for us to place PE image at expected image base, so we don't care about relocation. 3. Thread Simulation - We need to create a fake CPU unit to run every single instruction, and it's allowed us to monitor all behavior.

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>_Emu in Python 1. File Mapping - It's essential for codes to fetch information from each other section (e.g., [email protected] read [email protected]) ➛ via PEFile.py 2. Repair IAT - Repairing Import Address Table for malware to call WinAPI at correct address ➛ via Unicorn.py + PEFile.py + Keystone.py 3. Thread Simulation - We need to create a fake CPU unit to run every single instruction, and it's allowed us to monitor all behavior ➛ via Unicorn.py

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Unicorn is a lightweight multi-platform, multi-architecture CPU emulator framework. Highlight features: • Multi-architectures: Arm, Arm64, M68K, Mips, Sparc, x86, & x86_64. • Implemented in pure C language, with bindings for Crystal, Clojure, Visual Basic, Perl, Rust, Haskell, Ruby, Python, Java, Go, .NET, Delphi/Pascal & MSVC available. • Native support for Windows & *nix (with Mac OSX, Linux, *BSD & Solaris confirmed). • High performance by using Just-In-Time compiler technique. • Thread-safe by design.
 ... Unicorn is based on QEMU, but it goes much further with a lot more to offer. >_Unicorn.py

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>_Unicorn.py

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Challenge 1 >_File Mapping

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DOS Program OptionalHeader NtHeader ... .ImageBase (0x400000) .SizeOfHeaders File Header .NumberOfSections .AddressOfEntryPoint SizeOfHeaders Section Header 1 (.text) ... sizeof(Section Header) = IMAGE_SIZEOF_SECTION_HEADER = 40(fixed) .SizeOfImage Section Header 2 Section Header 3 Section Data 1 (.text) .DataDirectory Exe File (PE)

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DOS Program NtHeader ... Section Header 1 (.text) ... Section Header 2 Section Header 3 Section Data 1 (.text) SectionHeader[i] = PIMAGE_SECTION_HEADER( NtHeader + sizeof(IMAGE_NT_HEADERS) + IMAGE_SIZEOF_SECTION_HEADER * index ); IMAGE SECTION HEADER .VirtualAddress .SizeOfRawData .PointerToRawData Exe File (PE)

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>_File Mapping

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>_File Mapping

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Challenge 2 >_Repair Import Address Table

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>_ls ./agenda DOS Program OptionalHeader NtHeader ... .ImageBase (0x400000) .SizeOfHeaders File Header .NumberOfSections .AddressOfEntryPoint SizeOfHeaders Section Header 1 (.text) ... sizeof(Section Header) = IMAGE_SIZEOF_SECTION_HEADER = 40(fixed) .SizeOfImage Section Header 2 Section Header 3 Section Data 1 (.text) .DataDirectory Exe File (PE)

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>_ls ./agenda DOS Program OptionalHeader NtHeader ... DataDirectory Export Directory index 0 Import Directory 1 Exception Directory 2 Security Directory Base Relocation Table Resource Directory Import Address Table 3 4 5 ... 12 ... IMAGE_DATA_DIRECTORY[16] typedef struct _IMAGE_DATA_DIRECTORY { DWORD VirtualAddress; DWORD Size; } IMAGE_DATA_DIRECTORY, *PIMAGE_DATA_DIRECTORY; Exe File (PE)

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>_ls ./agenda DOS Program OptionalHeader NtHeader ... DataDirectory index Import Address Table ... 12 ... typedef struct _IMAGE_DATA_DIRECTORY { DWORD VirtualAddress; DWORD Size; } IMAGE_DATA_DIRECTORY, *PIMAGE_DATA_DIRECTORY; .VirtualAddress .Size Exe File (PE)

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>_ls ./agenda DOS Program OptionalHeader NtHeader ... DataDirectory index Import Address Table ... 12 ... .VirtualAddress .Size IMAGE_IMPORT_DESCRIPTOR Exe File (PE)

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IMAGE_IMPORT_DESCRIPTOR Array IMAGE_IMPORT_DESCRIPTOR 1 IMAGE_IMPORT_DESCRIPTOR 2 IMAGE_IMPORT_DESCRIPTOR 3 ... \x00\x00\x00\x00\x00\x00\x00 Fixed Size Fixed Size Fixed Size OptionalHeader DataDirectory index Import Address Table 12 .VirtualAddress .Size sizeof(IMAGE_IMPORT_DESCRIPTOR) NT Header sizeof(Descriptor Array) Exe File (PE)

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typedef struct _IMAGE_IMPORT_DESCRIPTOR { union { DWORD Characteristics;// 0 for terminating null import descriptor DWORD OriginalFirstThunk;// RVA to original unbound IAT (PIMAGE_THUNK_DATA) } DUMMYUNIONNAME; DWORD TimeDateStamp;// 0 if not bound, // -1 if bound, and real date\time stamp // in IMAGE_DIRECTORY_ENTRY_BOUND_IMPORT (new BIND) // O.W. date/time stamp of DLL bound to (Old BIND) DWORD ForwarderChain; // -1 if no forwarders DWORD Name; DWORD FirstThunk; // RVA to IAT (if bound this IAT has actual addresses) } IMAGE_IMPORT_DESCRIPTOR; typedef IMAGE_IMPORT_DESCRIPTOR UNALIGNED *PIMAGE_IMPORT_DESCRIPTOR; IMAGE_IMPORT_DESCRIPTOR

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IMAGE_IMPORT_DESCRIPTOR 1 OptionalHeader DataDirectory index Import Address Table 12 .VirtualAddress .Size NT Header .OriginalFirstThunk .FirstThunk .Name (User32.dll) IMAGE_IMPORT_BY_NAME: MessageBoxA typedef struct _IMAGE_IMPORT_BY_NAME { WORD Hint; CHAR Name[1]; } IMAGE_IMPORT_BY_NAME; Exe File (PE)

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xor eax, eax ret push 0 push 0x40dead push 0x40beef push 0 call ds:0x40cafe IMAGE_IMPORT_DESCRIPTOR 1 OptionalHeader DataDirectory index Import Address Table 12 .VirtualAddress .Size NT Header .OriginalFirstThunk .FirstThunk = 0xcafe .Name (User32.dll) IMAGE_IMPORT_BY_NAME: MessageBoxA Exe File (PE)

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IMAGE_IMPORT_DESCRIPTOR 1 OptionalHeader DataDirectory index Import Address Table 12 .VirtualAddress .Size NT Header .FirstThunk = 0xcafe .FirstThunk .Name (User32.dll) IMAGE_IMPORT_BY_NAME: MessageBoxA HANDLE mod = LoadLibrary("User32.dll"); GetProcAddress(mod, "MessageBoxA") = 0x7547EA99 0x7547EA99 Exe File (PE)

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Thunk Array IMAGE_IMPORT_DESCRIPTOR 1 OptionalHeader DataDirectory index Import Address Table 12 .VirtualAddress .Size NT Header MessageBoxA: *(uint32_t *)0xcafe = 0x7547EA99 .FirstThunk = 0xcafe .Thunk = 0xcaff .Thunk = 0xcb00 .Thunk = 0xcb02 .Name (User32.dll) LoadStringA: *(uint32_t *)0xcaff = 0x75130D4D KillTimer: *(uint32_t *)0xcb01 = 0x754364C7 Lastest Thunk: *(uint32_t *)0xcb02 = NULL Exe File (PE)

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>_My Win32 Internal ˉ ̶̡̭̭ (´∀｀๑) ˉ ̶̡̭̭

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>_Repair IAT

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>_Repair IAT

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Challenge 3 >_Emulation Thread

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>_Thread Registers eax 41414141 ebx 42424242 ecx 43434343 edx 44444444 ... ... esp 7ffffffc ebp 7ffffffc eip 401000 Main.exe .text Section addr @ 401000: 6A 00 68 AD DE 40 00 68 EF BE 40 00 6A 00 FF 15 FE CA 40 00 33 C0 C3

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>_Periodic Table? sparksandflames.com/files/x86InstructionChart.html

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>_Thread addr @ 401000: 6A 00 68 AD DE 40 00 68 EF BE 40 00 6A 00 FF 15 FE CA 40 00 33 C0 C3 push 0 push 0x40dead push 0x40beef push 0 call ds:0x40cafe xor eax, eax ret via x86 Instruction Set Registers eax 41414141 ebx 42424242 ecx 43434343 edx 44444444 ... ... esp 7ffffffc ebp 7ffffffc eip 401000

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>_hook

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>_hook

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>_Emulation

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>_Downloader

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[email protected] Demo

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Challenge 4 >_TEB, PEB, LDR, ...

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>_Repair IAT

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>_Challenge 4

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[email protected] Recap

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>_Bypass blog.trendmicro.com/trendlabs-security-intelligence/new-emotet-hijacks-windows-api-evades-sandbox-analysis

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>_AV Leak hwww.youtube.com/watch?v=a6yOwvFds78

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>_Sandbox • VM-like Sandbox • Slow, resource consuming • Easily to be identified • Loader-like Sandbox • Not easy to implement whole system API • Cuckoo-like Sandbox • Not isolated environment, vulnerable

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Thanks! [email protected] Slide Github @aaaddress1 Facebook