Fuzzing attacks are automated attacks where as much as random data as possible is being send to a device or network to search for vulnerabilities by "guessing" strings that give access to the session or (file-)system. It typically looks at the response it gets on a request and the malwares' abilities it gets like reading, writing and executing certain files and directories. Typically, fuzzing is a technique that when succesful, can give a start-sign to intruders to deploy their malicious payload using the discovered vulnerability.