CVE-2023-28623

Zulip is an open-source team collaboration tool with unique topic-based threading. In the event that 1: 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 2: The organization permissions dont require invitations to join. An attacker can create a new account in the organization with an arbitrary email address in their control thats not in the organizations LDAP directory. The impact is limited to installations which have this specific combination of authentication backends as described above in addition to having Invitations are required for joining this organization organization permission disabled. This issue has been addressed in version 6.2. Users are advised to upgrade. Users unable to upgrade may enable the Invitations are required for joining this organization organization permission to prevent this issue.

Weakness

The product does not perform an authorization check when an actor attempts to access a resource or perform an action.

Affected Software

Extended Description

Assuming a user with a given identity, authorization is the process of determining whether that user can access a given resource, based on the user’s privileges and any permissions or other access-control specifications that apply to the resource. When access control checks are not applied, users are able to access data or perform actions that they should not be allowed to perform. This can lead to a wide range of problems, including information exposures, denial of service, and arbitrary code execution.

Potential Mitigations

• Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) [REF-229] to enforce the roles at the appropriate boundaries.
• Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
• For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page.
• One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/665.html

References

• https://github.com/zulip/zulip/commit/3df1b4dd7c210c21deb6f829df19412b74573f8d
• https://github.com/zulip/zulip/security/advisories/GHSA-7p62-pjwg-56rv