# CVE-2021-3967: Improper Access Control in zulip/zulip

> An attacker can bypass access controls in the Zulip chat platform to perform unauthorized actions.

- **Severity:** Medium 4.1 (`CVSS:3.0/AV:N/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 26 Feb 2022
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-2xp9-33rm-wcwv

## What is CVE-2021-3967?

CVE-2021-3967 is a medium-severity missing authorization vulnerability in zulip/zulip, published on 26 Feb 2022. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

Improper Access Control in GitHub repository zulip/zulip prior to 4.10.

Weakness: CWE-284 (Improper Access Control)

## Which versions are affected by CVE-2021-3967?

It affects 1 product.


Products: Zulip Zulip.

## How do I fix CVE-2021-3967?

No fix has been published for CVE-2021-3967 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-3967 being exploited?

There is no known exploitation of CVE-2021-3967 in the wild and no public exploit code.

## Other vulnerabilities in zulip/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-2023-28623](https://insights.sbomify.com/CVE-2023-28623/): Unauthorized user can register an account in specific configurations in Zulip (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3967 and fix it if it is affected.

What it is: CVE-2021-3967 is a medium-severity missing authorization vulnerability in zulip/zulip, published on 26 Feb 2022. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-3967 in the wild and no public exploit code.

Affected product: zulip/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-2021-3967/ (Markdown: https://insights.sbomify.com/CVE-2021-3967/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3967
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3967
- OSV: https://osv.dev/vulnerability/CVE-2021-3967

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3967/
Summaries are generated and may contain mistakes; the official description above is the record.