Zulip server before 2.0.5 incompletely validated the MIME types of...

Vulnerability Description

Zulip server before 2.0.5 incompletely validated the MIME types of uploaded files. A user who is logged into the server could upload files of certain types to mount a stored cross-site scripting attack on other logged-in users. On a Zulip server using the default local uploads backend, the attack is only effective against browsers lacking support for Content-Security-Policy such as Internet Explorer 11. On a Zulip server using the S3 uploads backend, the attack is confined to the origin of the configured S3 uploads hostname and cannot reach the Zulip server itself.

References

• https://blog.zulip.org/2019/09/11/zulip-server-2-0-5-security-release/
• https://github.com/zulip/zulip/commit/1195841dfb9aa26b3b0dabc6f05d72e4af25be3e