Email enumeration

How it was found

Navigate to the page - https://slack.com/signin Now, entering invalid email address returns an erroneous response. However, if you enter a valid email address like [email protected], it redirects you to a different page where it asks you to choose teams that belongs to [email protected]. You can then click on any option which will in turn redirect to that particular team's page on the slack domain like <teamname>.slack.com.

The above vulnerability can be used to enumerate email address of the users of the application as well as learn more about teams associated with that email address.