Please read carefully and check if the version of your Zammad system is affected by this vulnerability. Please send information regarding vulnerabilities in Zammad to: security at zammad.com
The Zammad application's Create User functionality is implemented in a way that would enable an anonymous user to guess valid user emails. In the current implementation, the application responds differently depending on whether the input supplied was recognized as associated with a valid user or not. This behavior could be used as part of a two-stage automated attack. During the first stage, an attacker would iterate through a list of account names to determine which correspond with valid accounts. During the second stage, the attacker would use this account for further actions.
This vulnerability is fixed in the latest versions of Zammad and it is recommended to upgrade to one of these.
Fixed releases can be found at:
Or just update your Zammad if installed via OS package manager.
Online version of this advisory: https://zammad.com/news/security-advisory-zaa-2020-14
Send all remarks to security issues to security @ zammad.com.