Raw vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:NCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2023-28623 is a medium-severity Improper Authorization (CWE-285) vulnerability in Zulip Zulip. Its CVSS base score is 6.5 (Medium).
Operationally, ranked at the 43th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2023-32291
Vulnerability Data
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…
more
organization permissions don't require invitations to join. An attacker can create a new account in the organization with an arbitrary email address in their control that's not in the organization's 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.
- CWE(s)
Related Threats
CVEs Like This One
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Documented procedures facilitate correct implementation and ongoing management of authorization decisions.
Periodic reviews identify and correct flaws in authorization decisions or enforcement.
Documenting permitted unauthenticated actions prevents missing authorization by making all exceptions explicit and subject to organizational review.
Establishing permitted attributes and values, plus auditing changes, ensures authorization decisions are based on correctly managed policy data.
Explicitly mandates authorizing remote access types before permitting connections, directly mitigating improper authorization.
The control explicitly requires authorization of each wireless access type prior to permitting connections.
Mandating explicit authorization of mobile device connections reduces the risk of improper authorization decisions for system access.
Specifying access authorizations for each account and requiring approvals for account requests enforces proper authorization decisions.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
A.5.1 only requires the existence of an overarching policy and topic-specific policies (including on access control); it does not itself perform or enforce any authorization check, so the CWE-285 weakness can still be exploited.
Mapping access rights to information classification and business requirements forces correct enforcement of authorization decisions, blocking the incorrect authorization weakness at the policy and implementation stage.
A.5.18's provisioning, review, revocation and activation steps (incl. owner approval, SoD, timely removal on role/termination change) directly stop exploitation of missing authorization checks by ensuring no actor receives or retains rights to resources they should not access; the bounded remainder is that it cannot stop missing-authorization defects inside the enforcement mechanism itself once rights have been granted (e.g. flawed code that ignores the rights table).
Independent reviewers evaluate whether authorization logic matches policy, thereby reducing the window in which incorrect or missing authorization checks remain in production.
By requiring managers to verify that authorization decisions match policy and to remediate deviations, the control limits the persistence of incorrect or missing authorization checks.
Requiring authorization processes and privilege assignments to be specified during project initiation prevents downstream components from receiving overly broad or incorrect rights that would allow unauthorized actions.
Hardening callouts derived
DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.
- No fine-grained STIG row for CWE-285, a class-level weakness. Rules are authored against its narrower children: CWE-552.
- No fine-grained STIG row for CWE-862, a class-level weakness, and none of its children carries one either.