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Thread: VMProtect, Part 0: Basics

  1. #1

    VMProtect, Part 0: Basics

    VMProtect is a virtualization protector. Like other protections in the genre, among others ReWolf's x86 Virtualizer and CodeVirtualizer, it works by disassembling the x86 bytecode of the target executable and compiling it into a proprietary, polymorphic bytecode which is executed in a custom interpreter at run-time. This is unlike the traditional notions of packing, in which the x86 bytecode is simply encrypted and/or compressed: with virtualization, the original x86 bytecode in the protected areas is gone, never to be seen again. Or so the idea goes.

    If you've never looked at VMProtect before, I encourage you to take a five-minute look in IDA (here's a sample packed binary). As far as VMs go, it is particularly skeletal and easily comprehended. The difficulty lies in recreating working x86 bytecode from the VM bytecode. Here's a two-minute analysis of its dispatcher.

      push  edi                        ; push all registers
      push  ecx
      push  edx
      push  esi
      push  ebp
      push  ebx
      push  eax
      push  edx
      push  0                          ; imagebase fixup
      mov   esi, [esp+8+arg_0]         ; esi = pointer to VM bytecode
      mov   ebp, esp                   ; ebp = VM's "stack" pointer
      sub   esp, 0C0h
      mov   edi, esp                   ; edi = "scratch" data area
      add   esi, [ebp+0]
      mov   al, [esi]                  ; read a byte from EIP
      movzx eax, al
      sub   esi, -1                    ; increment EIP
      jmp   ds:VM__HandlerTable[eax*4] ; execute instruction handler
    A feature worth discussing is the "scratch space", referenced by the register edi throughout the dispatch loop. This is a 16-dword-sized area on the stack where VMProtect saves the registers upon entering the VM, modifies them throughout the course of a basic block, and from whence it restores the registers upon exit. For each basic block protected by the VM, the layout of the registers in the scratch space can potentially be different.

    Here's a disassembly of some instruction handlers. Notice that A) VMProtect is a stack machine and that B) each handler -- though consisting of scant few instructions -- performs several tasks, e.g. popping several values, performing multiple operations, pushing one or more values.

    #00:  x = [EIP-1] & 0x3C; y = popd; [edi+x] = y
    .text:00427251   and   al, 3Ch        ; al = instruction number
    .text:00427254   mov   edx, [ebp+0]   ; grab a dword off the stack
    .text:00427257   add   ebp, 4         ; pop the stack
    .text:0042725A   mov   [edi+eax], edx ; store the dword in the scratch space
    #01:  x = [EIP-1] & 0x3C; y = [edi+x]; pushd y
    .vmp0:0046B0EB   and   al, 3Ch        ; al = instruction number
    .vmp0:0046B0EE   mov   edx, [edi+eax] ; grab a dword out of the scratch space
    .vmp0:0046B0F1   sub   ebp, 4         ; subtract 4 from the stack pointer
    .vmp0:0046B0F4   mov   [ebp+0], edx   ; push the dword onto the stack
    #02:  x = popw, y = popw, z = x + y, pushw z, pushf
    .text:004271FB   mov   ax, [ebp+0]       ; pop a word off the stack
    .text:004271FF   sub   ebp, 2
    .text:00427202   add   [ebp+4], ax       ; add it to another word on the stack
    .text:00427206   pushf                
    .text:00427207   pop   dword ptr [ebp+0] ; push the flags
    #03:  x = [EIP++]; w = popw; [edi+x] = Byte(w)
    .vmp0:0046B02A   movzx eax, byte ptr [esi] ; read a byte from EIP
    .vmp0:0046B02D   mov   dx, [ebp+0]         ; pop a word off the stack
    .vmp0:0046B031   inc   esi                 ; EIP++
    .vmp0:0046B032   add   ebp, 2              ; adjust stack pointer
    .vmp0:0046B035   mov   [edi+eax], dl       ; write a byte into the scratch area
    #04:  x = popd, y = popw, z = x << y, pushd z, pushf
    .vmp0:0046B095   mov   eax, [ebp+0]      ; pop a dword off the stack
    .vmp0:0046B098   mov   cl, [ebp+4]       ; pop a word off the stack
    .vmp0:0046B09B   sub   ebp, 2
    .vmp0:0046B09E   shr   eax, cl           ; shr the dword by the word
    .vmp0:0046B0A0   mov   [ebp+4], eax      ; push the result
    .vmp0:0046B0A3   pushf
    .vmp0:0046B0A4   pop   dword ptr [ebp+0] ; push the flags
    #05:  x = popd, pushd ss:[x]
    .vmp0:0046B5F7   mov   eax, [ebp+0]  ; pop a dword off the stack
    .vmp0:0046B5FA   mov   eax, ss:[eax] ; read a dword from ss
    .vmp0:0046B5FD   mov   [ebp+0], eax  ; push that dword,_Part_0:__Basics

  2. #2
    Musician member evaluator's Avatar
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    hey, was there need for discover VMProtect!?
    i mean, how many SOFTWARE you found protected with it?

  3. #3
    I'm interested in it because of malware analysis, not cracking. There's enough of it in malware to justify the time expenditure.

  4. #4
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    thanks for replay!

    my Q was not about cracking interest, it was about unpacker_work;

    that is surprise! so VMProtect used in malware!?
    can you point exactly to that ones? are they protected by DEMO vers

  5. #5
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    well there are many craps protected by virtualwhatever available you can check one that was recently posted by naides in malware analysis forum that uses oreans's product
    handler #77 in that exe executes LoadLibrary etc

    its vm aware so be careful

    005019D7 2C 35 SUB AL, 35
    005019D9 04 F4 ADD AL, 0F4
    005019DB 00D0 ADD AL, DL
    005019DD 2C F4 SUB AL, 0F4
    005019DF 04 35 ADD AL, 35
    005019E1 5A POP EDX ; 0012FFF0
    005019E2 30C3 XOR BL, AL
    005019E4 0FB6C0 MOVZX EAX, AL
    005019E7 <looper> FF2487 JMP NEAR DWORD PTR DS:[EDI+EAX*4]

    004FC2D2 <jumptablebase> F6EF45C8 E
    004FC2D6 <jt1> 0052CD04 R. DiskInte.0052CD04
    004FC2DA <jt2> 004F61BD aO. DiskInte.004F61BD
    004FC2DE <jt3> FFFF9E7C |ž
    004FC2E2 <jt4> 00000001 ...
    004FC2E6 <jt5> FFFFFFFF
    004FC2EA <jt6> 7C809B77 w›€| kernel32.CloseHandle
    004FC2EE <jt7> 00000213 ..
    004FC2F2 <jt8> 00000002 ...
    004FC2F6 <jt9> 00000001 ...
    004FC2FA <jt10> 00000004 ...
    004FC2FE <jt11> F6EF45C8 E
    004FC302 <jt12> 00000000 ....
    004FC306 <jt13> 00000000 ....
    004FC30A <jt14> 00000000 ....
    004FC30E <jt15> 00000000 ....
    004FC312 <jt16> 00000000 ....
    004FC316 <jt17> 00502F2E ./P. DiskInte.00502F2E

    [here is the complete handler sequence for that #

    004FFFDD             FF77 38         PUSH    DWORD PTR DS:[EDI+38]
    004FFFE0             812C24 4D17CD7A SUB     DWORD PTR SS:[ESP], 7ACD174D
    004FFFE7             59              POP     ECX
    004FFFE8             52              PUSH    EDX
    004FFFE9             57              PUSH    EDI                                          ; <DiskInte.jumptablebase>
    004FFFEA             53              PUSH    EBX
    004FFFEB             68 1E34415E     PUSH    5E41341E
    004FFFF0             5B              POP     EBX
    004FFFF1             43              INC     EBX
    004FFFF2           ^ E9 B9E6FFFF     JMP     DiskInte.004FE6B0
    004FE6B0             81C3 0E430EF3   ADD     EBX, F30E430E
    004FE6B6             89DF            MOV     EDI, EBX
    004FE6B8             5B              POP     EBX
    004FE6B9             4F              DEC     EDI                                          ; <DiskInte.jumptablebase>
    004FE6BA             4F              DEC     EDI                                          ; <DiskInte.jumptablebase>
    004FE6BB             81F7 6258946F   XOR     EDI, 6F945862
    004FE6C1             81C7 2C42431B   ADD     EDI, 1B43422C
    004FE6C7             53              PUSH    EBX
    004FE6C8             BB 3B29B545     MOV     EBX, 45B5293B
    004FE6CD             29DF            SUB     EDI, EBX
    004FE6CF             5B              POP     EBX
    004FE6D0             89FA            MOV     EDX, EDI                                     ; <DiskInte.jumptablebase>
    004FE6D2             5F              POP     EDI                                          ; <DiskInte.jumptablebase>
    004FE6D3             F7D2            NOT     EDX
    004FE6D5             C1E2 08         SHL     EDX, 8
    004FE6D8             68 08610000     PUSH    6108
    004FE6DD             E9 DE210000     JMP     DiskInte.005008C0
    005008C0             891C24          MOV     DWORD PTR SS:[ESP], EBX
    005008C3             BB FF675D60     MOV     EBX, 605D67FF
    005008C8             31DA            XOR     EDX, EBX
    005008CA             5B              POP     EBX
    005008CB             50              PUSH    EAX
    005008CC             53              PUSH    EBX
    005008CD             BB 27729B27     MOV     EBX, 279B7227
    005008D2             4B              DEC     EBX
    005008D3             81E3 6913C834   AND     EBX, 34C81369
    005008D9             55              PUSH    EBP
    005008DA             E9 CA050000     JMP     DiskInte.00500EA9
    00500EA9             BD 591FEE6C     MOV     EBP, 6CEE1F59
    00500EAE             E9 28090000     JMP     DiskInte.005017DB
    005017DB             81ED 5EC04A21   SUB     EBP, 214AC05E
    005017E1             31EB            XOR     EBX, EBP
    005017E3             5D              POP     EBP
    005017E4             89D8            MOV     EAX, EBX
    005017E6             5B              POP     EBX
    005017E7             E9 B35B0000     JMP     DiskInte.0050739F
    0050739F             51              PUSH    ECX
    005073A0           ^ E9 377DFFFF     JMP     DiskInte.004FF0DC
    004FF0DC             B9 9828C556     MOV     ECX, 56C52898
    004FF0E1             81E9 C7D78800   SUB     ECX, 88D7C7
    004FF0E7             E9 E61A0000     JMP     DiskInte.00500BD2
    00500BD2             09C8            OR      EAX, ECX
    00500BD4             59              POP     ECX
    00500BD5             C1E0 04         SHL     EAX, 4
    00500BD8             2D 7E6D3889     SUB     EAX, 89386D7E
    00500BDD             E9 15390000     JMP     DiskInte.005044F7
    005044F7             81C2 0A3E4C29   ADD     EDX, 294C3E0A
    005044FD             01C2            ADD     EDX, EAX
    005088D6             81EA 0A3E4C29   SUB     EDX, 294C3E0A
    005088DC             58              POP     EAX
    005088DD             81EA E4EBDAE6   SUB     EDX, E6DAEBE4
    005088E3             01D1            ADD     ECX, EDX
    005088E5             5A              POP     EDX
    005088E6             68 D1770000     PUSH    77D1
    005088EB             893C24          MOV     DWORD PTR SS:[ESP], EDI                      ; <DiskInte.jumptablebase>
    005088EE             FF3424          PUSH    DWORD PTR SS:[ESP]
    005088F1             5A              POP     EDX
    005088F2             55              PUSH    EBP
    005088F3             54              PUSH    ESP
    005088F4           ^ E9 6990FFFF     JMP     DiskInte.00501962
    00501962             5D              POP     EBP
    00501963             57              PUSH    EDI                                          ; <DiskInte.jumptablebase>
    00501964           ^ E9 40B0FFFF     JMP     DiskInte.004FC9A9
    004FC9A9             BF 28375724     MOV     EDI, 24573728
    004FC9AE             C1EF 08         SHR     EDI, 8
    004FC9B1             81CF A00BA966   OR      EDI, 66A90BA0
    004FC9B7             81F7 DF3E491B   XOR     EDI, 1B493EDF
    004FC9BD             E9 6FA20000     JMP     DiskInte.00506C31
    00506C31             47              INC     EDI                                          ; <DiskInte.jumptablebase>
    00506C32             81F7 6D61E47D   XOR     EDI, 7DE4616D
    00506C38           ^ E9 8A81FFFF     JMP     DiskInte.004FEDC7
    004FEDC7             01FD            ADD     EBP, EDI                                     ; <DiskInte.jumptablebase>
    004FEDC9             5F              POP     EDI                                          ; <DiskInte.jumptablebase>
    004FEDCA             81ED 04000000   SUB     EBP, 4
    004FEDD0             872C24          XCHG    DWORD PTR SS:[ESP], EBP
    004FEDD3             5C              POP     ESP
    004FEDD4           ^ E9 DEDFFFFF     JMP     DiskInte.004FCDB7
    004FCDB7             890C24          MOV     DWORD PTR SS:[ESP], ECX
    004FCDBA             83EC 04         SUB     ESP, 4
    004FCDBD             892424          MOV     DWORD PTR SS:[ESP], ESP
    004FCDC0             810424 04000000 ADD     DWORD PTR SS:[ESP], 4
    004FCDC7             59              POP     ECX
    004FCDC8             81C1 04000000   ADD     ECX, 4
    004FCDCE             52              PUSH    EDX
    004FCDCF             BA 04000000     MOV     EDX, 4
    004FCDD4             01D1            ADD     ECX, EDX
    004FCDD6             5A              POP     EDX
    004FCDD7             870C24          XCHG    DWORD PTR SS:[ESP], ECX
    004FCDDA             5C              POP     ESP
    004FCDDB             09C9            OR      ECX, ECX
    004FCDDD             0F84 8C7A0000   JE      DiskInte.0050486F  <--- this always had jumped 
    0050486F             C742 30 AF0CB55>MOV     DWORD PTR DS:[EDX+30], 5CB50CAF
    00504876             E9 963D0000     JMP     DiskInte.00508611
    00508611             816A 30 03736D0>SUB     DWORD PTR DS:[EDX+30], 6D7303
    00508618             FF72 30         PUSH    DWORD PTR DS:[EDX+30]
    0050861B             53              PUSH    EBX
    0050861C             BB 01000000     MOV     EBX, 1
    00508621             816C24 04 B95B6>SUB     DWORD PTR SS:[ESP+4], 57685BB9
    00508629             295C24 04       SUB     DWORD PTR SS:[ESP+4], EBX
    0050862D             814424 04 B95B6>ADD     DWORD PTR SS:[ESP+4], 57685BB9
    00508635             5B              POP     EBX
    00508636             8F42 30         POP     DWORD PTR DS:[EDX+30]
    00508639             50              PUSH    EAX
    0050863A             B8 753C6E19     MOV     EAX, 196E3C75
    0050863F           ^ E9 35FCFFFF     JMP     DiskInte.00508279
    00508279             55              PUSH    EBP
    0050827A             BD 0D0BB94B     MOV     EBP, 4BB90B0D
    0050827F           ^ E9 DC84FFFF     JMP     DiskInte.00500760
    00500760             F7DD            NEG     EBP
    00500762           ^ E9 8BE9FFFF     JMP     DiskInte.004FF0F2
    004FF0F2             81E5 91649742   AND     EBP, 42976491
    004FF0F8             81C5 E53D4A2A   ADD     EBP, 2A4A3DE5
    004FF0FE             81CD 3429005F   OR      EBP, 5F002934
    004FF104             81C5 1943657D   ADD     EBP, 7D654319
    004FF10A             81F5 31E16CEC   XOR     EBP, EC6CE131
    004FF110             29E8            SUB     EAX, EBP
    004FF112             5D              POP     EBP
    004FF113             0942 30         OR      DWORD PTR DS:[EDX+30], EAX
    004FF116             58              POP     EAX
    004FF117             68 D35B0000     PUSH    5BD3
    004FF11C             893424          MOV     DWORD PTR SS:[ESP], ESI                      ; DiskInte.0052F503
    004FF11F             E9 1C780000     JMP     DiskInte.00506940
    00506940             BE 2E45242C     MOV     ESI, 2C24452E
    00506945           ^ E9 A7EAFFFF     JMP     DiskInte.005053F1
    005053F1             F7D6            NOT     ESI                                          ; DiskInte.0052F503
    005053F3             E9 71360000     JMP     DiskInte.00508A69
    00508A69             D1E6            SHL     ESI, 1
    00508A6B             81EE 12329B7D   SUB     ESI, 7D9B3212
    00508A71             68 794B0000     PUSH    4B79
    00508A76             892C24          MOV     DWORD PTR SS:[ESP], EBP
    00508A79             BD 217F5560     MOV     EBP, 60557F21
    00508A7E             21EE            AND     ESI, EBP
    00508A80             5D              POP     EBP
    00508A81           ^ E9 EF3EFFFF     JMP     DiskInte.004FC975
    004FC975             81F6 4A156800   XOR     ESI, 68154A
    004FC97B             2172 30         AND     DWORD PTR DS:[EDX+30], ESI                   ; DiskInte.0052F503
    004FC97E             E9 16240000     JMP     DiskInte.004FED99
    004FED99             8B3424          MOV     ESI, DWORD PTR SS:[ESP]
    004FED9C             83C4 04         ADD     ESP, 4
    004FED9F             816A 30 0A14540>SUB     DWORD PTR DS:[EDX+30], DiskInte.0054140A
    004FEDA6             61              POPAD
    004FEDA7             9D              POPFD
    004FEDA8             C3              RETN  <--- will go to system dll calls like loadlib,closehandle etc
    rolf if this disassembly snippet is similar to vmprotect can you try unobfuscate it ? i mean bring out the original sequence of x86 opcodes

  6. #6
    Musician member evaluator's Avatar
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    we are talking exactly about VMProtect;
    VM_code of oreans" is it's subject, i see it there..

    my main thought is: MALWARE using VM will NOT achieve any greats!
    malware must use "malicious" API, so that's all you need to detect;

    WriteProcessMemory2otherProcess = MALWARE/Virus

    other is VMcode in normal program, where it tries to hide IMPORTANT code from you..

  7. #7
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    Great work RolfRolles!!!

    I was always looking for good VMProtect material, truly important pieces of
    malware uses it, especially Rootkit Vectors as Srizbi

    Giuseppe Bonfa' (Repository)

  8. #8
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    as i seen, that is 90% LOADER code released in VM-code in Themida!

    STUPIDEST action even..
    .. in loaders history>>;D

  9. #9
    Great work RolfRolles as alwasy :P

    evaluator: stop typing bs..thx

  10. #10
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    evilcry, i failed to find Srizbi for dld..

  11. #11
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    you can download some sample of Srizbi from OffensiveComputing,
    here some link:

    and here some other MD5 hash to push in OC's search engine:


    Last edited by evilcry; August 9th, 2008 at 04:13. (Repository)

  12. #12
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    i played liittle with it, dumped DRV, but too many (3?) VM there, 1 virtualized loader, after then should be virtualized INIT..

    but look here, is this sure VMprotect from ?

  13. #13
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    but look here, is this sure VMprotect from ?
    Yes, I think is 1.6x or 1.5x Version but surely RolfRolles knows better its characteristics (Repository)

  14. #14
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    strange, i dlded last VMprotect & its code looks as written in first post!
    in this driver is other code.. (full version VMcode?)

    BTW, unpacked driver.. what now!? ~ ; D

  15. #15
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    ya, i just traced demo_protected example from included "examples", cool~
    opcodes are different on new compile, .. good work done by author, BTW!

    now, as i understand, virus was protected by full version,
    where this main VMinterpreter_code was junked_mutated, VM_opcodes crypted;

    but while tracing demo e.g. clean VM_interpreter, i guess:
    mainly, there is NO single VM_opcode for some real instruction.
    even more, there done fake calculations-comparisions-junkVMcode!

    so, all this greatly works against one_automated solution.

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