This is the simplest base64 encoding, just google it, it's very easy to decode. The decoded code simply contains the WSO web shell code: https://ghostbin.com/6WEmK/raw
https://www.sendspace.com/file/34pequ I made some edits to the file to decode it. Just run this script in your environment and the result will be in "encoded_result.txt" file. But again, this is also the encoded "WSO" web shell code.