Security Resilience

CVE-2023-28623

Access Control in Zulip ≤ 6.2

Published
19 May 2023
Modified
21 November 2024
Patch / advisory
CVSS Score v3.1 6.5
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
EPSS Score 0.0053 43th percentile
Risk Priority 50 floored blend · peak EPSS

CVSS 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

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

CVE-2023-32677Same product: Zulip Zulip
CVE-2023-32678Same vendor: Zulip
CVE-2024-21630Same vendor: Zulip
CVE-2024-5053Shared CWE-285, CWE-862
CVE-2023-30948Shared CWE-285, CWE-862
CVE-2025-29926Shared CWE-285, CWE-862
CVE-2026-86283Shared CWE-285, CWE-862
CVE-2026-30956Shared CWE-285, CWE-862
CVE-2026-84314Shared CWE-285, CWE-862
CVE-2026-45371Shared CWE-285, CWE-862

Affected Assets

zulip
zulip
≤ 6.2

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.

addresses: CWE-285 CWE-862

Documented procedures facilitate correct implementation and ongoing management of authorization decisions.

addresses: CWE-285 CWE-862

Periodic reviews identify and correct flaws in authorization decisions or enforcement.

addresses: CWE-862 CWE-285

Documenting permitted unauthenticated actions prevents missing authorization by making all exceptions explicit and subject to organizational review.

addresses: CWE-285 CWE-862

Establishing permitted attributes and values, plus auditing changes, ensures authorization decisions are based on correctly managed policy data.

addresses: CWE-285 CWE-862

Explicitly mandates authorizing remote access types before permitting connections, directly mitigating improper authorization.

addresses: CWE-285 CWE-862

The control explicitly requires authorization of each wireless access type prior to permitting connections.

addresses: CWE-285 CWE-862

Mandating explicit authorization of mobile device connections reduces the risk of improper authorization decisions for system access.

addresses: CWE-285 CWE-862

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.

blocks

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.

blocks

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.

blocks

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).

finds

Independent reviewers evaluate whether authorization logic matches policy, thereby reducing the window in which incorrect or missing authorization checks remain in production.

finds

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.

blocks

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.

References