Security restrictions bypass in Zulip Server

1) Improper access control

EUVDB-ID: #VU65858

Risk: Low

CVSSv4.0: 1.3 [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]

CVE-ID: CVE-2017-0881

CWE-ID: CWE-284 - Improper Access Control

Exploit availability: No

Description

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.

Mitigation

Install updates from vendor's website.

Vulnerable software versions

Zulip Server: 1.1.5 - 1.4.2

CPE2.3

• cpe:2.3:a:zulip:zulip_server:1.1.5:*:*:*:*:*:*:*
• cpe:2.3:a:zulip:zulip_server:1.2.0:*:*:*:*:*:*:*
• cpe:2.3:a:zulip:zulip_server:1.2.0 p1:*:*:*:*:*:*:*

External links

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

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote authenticated user via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.