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 SSO endpoint is used to create sessions for requests authenticated by a third party system via SSO. An attacker could send a special header to the SSO endpoint in systems that don't have SSO configured. The request would then create a valid and authenticated session that can be used to perform any actions in the name of other users. However, the user would be notified that a new device performed a login.
Special 🙏 and 🤘 and ❤️ to:
N: Dmitry Sobolev
D: Security Researcher
It's recommended to update existing Webserver/Reverse Proxies installations that can't be updated automatically.
For NginX: Extend your "server" block with "proxy_set_header X-Forwarded-User "";" as in https://github.com/zammad/zammad/blob/develop/contrib/nginx/zammad.conf
For Apache2: Extend your "VirtualHost" with "RequestHeader unset X-Forwarded-User" as in https://github.com/zammad/zammad/blob/develop/contrib/apache2/zammad_ssl.conf
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-2020-18
Send all remarks to security issues to security @ zammad.com.