# CVE-2023-28623: Unauthorized user can register an account in specific configurations in Zulip

> Attackers can register unauthorized accounts in Zulip when specific LDAP and external authentication backends are enabled without invitation requirements.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 19 May 2023
- **Updated:** 12 Feb 2025
- **Also known as:** GHSA-7p62-pjwg-56rv

## What is CVE-2023-28623?

CVE-2023-28623 is a medium-severity authentication bypass vulnerability in zulip, published on 19 May 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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 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.

Weakness: CWE-862 (Missing Authorization), CWE-285 (Improper Authorization)

## Which versions are affected by CVE-2023-28623?

It affects 1 product.


Products: Zulip Zulip.

## How do I fix CVE-2023-28623?

No fix has been published for CVE-2023-28623 yet. Limit exposure of the affected software until one is available.

## Is CVE-2023-28623 being exploited?

There is no known exploitation of CVE-2023-28623 in the wild and no public exploit code.

## Other vulnerabilities in zulip

- [CVE-2021-43799](https://insights.sbomify.com/CVE-2021-43799/): RabbitMQ exposes ports with weak default secrets in Zulip Server (high 8.6)
- [CVE-2022-35962](https://insights.sbomify.com/CVE-2022-35962/): Crafted link in Zulip message can cause disclosure of credentials (high 8.0)
- [CVE-2016-4427](https://insights.sbomify.com/CVE-2016-4427/): Auth bypass in zulip (high 7.5)
- [CVE-2021-3866](https://insights.sbomify.com/CVE-2021-3866/): Cross-site Scripting (XSS) - Stored in zulip/zulip (medium 6.8)
- [CVE-2021-43791](https://insights.sbomify.com/CVE-2021-43791/): Ineffective expiration validation for invitation links in Zulip (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-28623 and fix it if it is affected.

What it is: CVE-2023-28623 is a medium-severity authentication bypass vulnerability in zulip, published on 19 May 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-28623 in the wild and no public exploit code.

Affected product: zulip. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2023-28623/ (Markdown: https://insights.sbomify.com/CVE-2023-28623/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-28623
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-28623
- OSV: https://osv.dev/vulnerability/CVE-2023-28623

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-28623/
Summaries are generated and may contain mistakes; the official description above is the record.