# CVE-2021-43791: Ineffective expiration validation for invitation links in Zulip

> Attackers can register accounts using expired invitation links due to missing validation in the registration endpoint, allowing unauthorized access.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/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:** 2 Dec 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-wj76-pcqr-mf9f

## What is CVE-2021-43791?

CVE-2021-43791 is a medium-severity vulnerability in zulip, published on 2 Dec 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Zulip is an open source group chat application that combines real-time chat with threaded conversations. In affected versions expiration dates on the confirmation objects associated with email invitations were not enforced properly in the new account registration flow. A confirmation link takes a user to the check_prereg_key_and_redirect endpoint, before getting redirected to POST to /accounts/register/. The problem was that validation was happening in the check_prereg_key_and_redirect part and not in /accounts/register/ - meaning that one could submit an expired confirmation key and be able to register. The issue is fixed in Zulip 4.8. There are no known workarounds and users are advised to upgrade as soon as possible.

Weakness: CWE-613 (DEPRECATED: Insufficient Session Expiration)

## Which versions are affected by CVE-2021-43791?

It affects 1 product.


Products: Zulip Zulip.

## How do I fix CVE-2021-43791?

No fix has been published for CVE-2021-43791 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-43791 being exploited?

There is no known exploitation of CVE-2021-43791 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-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-2021-43791 and fix it if it is affected.

What it is: CVE-2021-43791 is a medium-severity vulnerability in zulip, published on 2 Dec 2021. 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-2021-43791 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-2021-43791/ (Markdown: https://insights.sbomify.com/CVE-2021-43791/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-43791
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-43791
- OSV: https://osv.dev/vulnerability/CVE-2021-43791

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-43791/
Summaries are generated and may contain mistakes; the official description above is the record.