SB2017032820 - Security restrictions bypass in Zulip Server

Description

This security bulletin contains information about 1 vulnerability.

1) Improper access control (CVE-ID: CVE-2017-0881)

CWE-ID: CWE-284 - Improper Access Control

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear

The vulnerability allows a remote user to gain unauthorized access to otherwise restricted functionality.

The vulnerability exists due to improper access restrictions in the autosubscribe feature in the check_stream_exists route of the Zulip group chat application server. A remote user can bypass implemented security restrictions and subscribe to a private stream without the necessary invitation from the group member.

Remediation

Install update from vendor's website.

References

• http://www.securityfocus.com/bid/97159
• https://github.com/zulip/zulip/commit/7ecda1ac8e26d8fb3725e954b2dc4723dda2255f
• https://groups.google.com/d/msg/zulip-announce/VyawgRuoY34/NTBwnTArGwAJ