The arbitrary code execution in DXE driver.

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Consider the vulnerability on the example of the AMITSE driver (file GUID: b1da0adf-4f77-4070-a88e-bffe1c60529a).

The pseudocode for vulnerable function is shown below (function address: 0x16520).

__int64 sub_16520()
{
  // [COLLAPSED LOCAL DECLARATIONS. PRESS KEYPAD CTRL-"+" TO EXPAND]

  GetPackageListHandle = gEsaVarPtr01;
  Arg2 = 0;
  Guid[0] = 0x70E1A818;
  Guid[1] = 0x44490BE1;
  Guid[2] = 0xF69ED4BF;
  Guid[3] = 0xA8027F8C;
  VendorGuid.Data1 = 0xA2DF5376;
  *&VendorGuid.Data2 = 0x49C0C2ED;
  *VendorGuid.Data4 = 0x178BFF90;
  *&VendorGuid.Data4[4] = 0x66D00F3B;
  if ( gEsaVarPtr01
    || (DataSize = 8,
        gRT->GetVariable(L"EsaVarPtr01", &VendorGuid, 0, &DataSize, &gEsaVarPtr01),
        (GetPackageListHandle = gEsaVarPtr01) != 0) )
  {
    Handle = GetPackageListHandle(Guid, &Arg2);
  }
  else
  {
    Handle = -1;
  }
  if ( Handle != -1 )
    return gEfiHiiDatabaseProtocol->RemovePackageList(gEfiHiiDatabaseProtocol, Handle);
  return Handle;
}

As we can see from the pseudocode, the address of GetPackageListHandle function located in the NVRAM variable EsaVarPtr01. Thus, a potential attacker can create the NVRAM variable EsaVarPtr01 and specify the address of the GetPackageListHandle function inside the data of the variable EsaVarPtr01. Thus, an attacker can execute arbitrary code during DXE phase.

It should be noted that the value of the variable EsaVarPtr01 cannot be set at runtime, but it can be set by physically modifying the SPI flash memory.

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This bug is subject to a 90 day disclosure deadline. After 90 days elapsed or a patch has been made broadly available (whichever is earlier), the bug report will become visible to the public.

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BINARLY efiXplorer team

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