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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

Security Advisory Details

Vulnerability Descriptions

Authentication bypass in SSO endpoint

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

Recommended Resolution

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

For Apache2: Extend your "VirtualHost" with "RequestHeader unset X-Forwarded-User" as in

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.

Additional information

Online version of this advisory:

Send all remarks to security issues to security @