Multiple vulnerabilities in Zulip Server

Published: 2019-09-18 | Updated: 2020-07-17

Risk	Medium
Patch available	YES
Number of vulnerabilities	2
CVE-ID	CVE-2019-16215 CVE-2019-16216
CWE-ID	CWE-400 CWE-79
Exploitation vector	Network
Public exploit	N/A
Vulnerable software Subscribe	Zulip Server Web applications / Other software
Vendor	Zulip

Security Bulletin

This security bulletin contains information about 2 vulnerabilities.

1) Resource exhaustion

EUVDB-ID: #VU30742

Risk: Medium

CVSSv3.1: 5.7 [CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C]

CVE-ID: CVE-2019-16215

CWE-ID: CWE-400 - Resource exhaustion

Exploit availability: No

Description

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.

Mitigation

Install update from vendor's website.

Vulnerable software versions

Zulip Server: 2.0.0 - 2.0.4

CPE2.3

External links

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

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.

2) Cross-site scripting

EUVDB-ID: #VU30743

Risk: Low

CVSSv3.1: 4.7 [CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N/E:U/RL:O/RC:C]

CVE-ID: CVE-2019-16216

CWE-ID: CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Exploit availability: No

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.

Mitigation

Install update from vendor's website.

Vulnerable software versions

Zulip Server: 1.8.0 - 2.0.4

CPE2.3

External links

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

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.