#VU52318 Improper access control in Zulip Server - CVE-2021-30477

Vulnerability identifier: #VU52318

Vulnerability risk: Medium

CVSSv4.0: 2.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2021-30477

CWE-ID: CWE-284

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Zulip Server
Web applications / Other software

Vendor: Zulip

Description

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

The vulnerability exists due to improper access restrictions in the implementation of replies to messages sent by outgoing webhooks to private streams. A remote attacker can use an outgoing webhook bot to send messages to private streams.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Zulip Server: 3.0 - 3.3

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External links
https://blog.zulip.com/2021/04/14/zulip-server-3-4/

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

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