Check this answer from unclemeat and comment from TessellatingHeckler in this thread

for /f "usebackq tokens=*" %%p in (`powershell -Command "$pword = read-host 'Enter Password' -AsSecureString ; $BSTR=[System.Runtime.InteropServices.Marshal]::SecureStringToBSTR($pword); [System.Runtime.InteropServices.Marshal]::PtrToStringAuto($BSTR)"`) do set password=%%p
echo %password%