Cross-site scripting in Zulip Server - CVE-2019-16216

Detailed vulnerability description

The vulnerability allows a remote authenticated user to read and manipulate data.

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.

How to mitigate CVE-2019-16216

Sources

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