Vulnerability identifier: #VU76393

Vulnerability risk: Medium

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

CVE-ID: CVE-2023-28623

CWE-ID: CWE-285

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Zulip Server
Web applications / Other software

Vendor: Zulip

Description

The vulnerability allows a remote attacker to bypass authorization checks.

The vulnerability exists due to an error in the registration process. A remote attacker can register a new account in the organization with an arbitrary email address in their control that's not in the organization's LDAP directory.

Successful exploitation of the vulnerability requires that ZulipLDAPAuthBackend and an external authentication backend (any aside of ZulipLDAPAuthBackend and EmailAuthBackend) are the only ones enabled in AUTHENTICATION_BACKENDS in /etc/zulip/settings.py and that the organization permissions don't require invitations to join.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Zulip Server: 2.1.0 - 6.1

---

External links
http://github.com/zulip/zulip/commit/3df1b4dd7c210c21deb6f829df19412b74573f8d
http://github.com/zulip/zulip/security/advisories/GHSA-7p62-pjwg-56rv
http://github.com/zulip/zulip/releases/tag/6.2

---

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.