In-band vs Out-band

In-band ​

In-Band refers to the same method of communication being used to exploit the vulnerability and also receive the results

For example, discovering an sqli vulnerability on a website page and then being able to extract data from the database to the same page.

Out-of-band ​

An Out-Of-Band attack is classified by having two different communication channels, one to launch the attack and the other to gather the results, eg. the attack channel could be a web request, and the data gathering channel could be monitoring HTTP/DNS requests made to a service we control.

1. An attacker makes a request to a website vulnerable to SQL Injection with an injection payload.
2. The Website makes a query to the DB which also passes the payload.
3. The payload contains a request which forces an HTTP request back to the hacker's machine containing data from the DB.