SB2019091813 - Multiple vulnerabilities in Zulip Server

Description

This security bulletin contains information about 2 secuirty vulnerabilities.

1) Resource exhaustion (CVE-ID: CVE-2019-16215)

The vulnerability allows a remote authenticated user to perform a denial of service (DoS) attack.

The Markdown parser in Zulip server before 2.0.5 used a regular expression vulnerable to exponential backtracking. A user who is logged into the server could send a crafted message causing the server to spend an effectively arbitrary amount of CPU time and stall the processing of future messages.

2) Cross-site scripting (CVE-ID: CVE-2019-16216)

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.

Remediation

Install update from vendor's website.

References

• https://blog.zulip.org/2019/09/11/zulip-server-2-0-5-security-release/
• https://github.com/zulip/zulip/commit/5797f013b3be450c146a4141514bda525f2f1b51
• https://github.com/zulip/zulip/commit/1195841dfb9aa26b3b0dabc6f05d72e4af25be3e