# CVE-2021-37631: Circle can be accessed by non-Circle members in Nextcloud Deck

> Attackers can access boards shared with a Circle without being members, exposing sensitive project data in Nextcloud Deck.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 7 Sep 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-4mxp-j277-82hr

## What is CVE-2021-37631?

CVE-2021-37631 is a medium-severity missing authorization vulnerability in nextcloud security-advisories, published on 7 Sep 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Deck is an open source kanban style organization tool aimed at personal planning and project organization for teams integrated with Nextcloud. In affected versions the Deck application didn't properly check membership of users in a Circle. This allowed other users in the instance to gain access to boards that have been shared with a Circle, even if the user was not a member of the circle. It is recommended that Nextcloud Deck is upgraded to 1.5.1, 1.4.4 or 1.2.9. If you are unable to update it is advised to disable the Deck plugin.

Weakness: CWE-639 (Authorization Bypass Through User-Controlled Key)

## Which versions are affected by CVE-2021-37631?

It affects 1 product.


Products: Nextcloud Deck.

## How do I fix CVE-2021-37631?

No fix has been published for CVE-2021-37631 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-37631 being exploited?

There is no known exploitation of CVE-2021-37631 in the wild and no public exploit code.

## Other vulnerabilities in nextcloud security-advisories

- [CVE-2021-39225](https://insights.sbomify.com/CVE-2021-39225/): Missing permission check on Deck API (high 8.1)
- [CVE-2020-8182](https://insights.sbomify.com/CVE-2020-8182/): Missing authorization in Nextcloud Deck (high 8.0)
- [CVE-2021-22913](https://insights.sbomify.com/CVE-2021-22913/): Information disclosure in Nextcloud Deck (medium 6.5)
- [CVE-2023-22469](https://insights.sbomify.com/CVE-2023-22469/): Nextcloud Deck card vulnerable to data leak to unauthorized users via reference preview cache (medium 5.8)
- [CVE-2025-66557](https://insights.sbomify.com/CVE-2025-66557/): Nextcloud Deck app allowed user with "Can share" permission to modify permissions of other non-owners (medium 5.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-37631 and fix it if it is affected.

What it is: CVE-2021-37631 is a medium-severity missing authorization vulnerability in nextcloud security-advisories, published on 7 Sep 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-37631 in the wild and no public exploit code.

Affected product: nextcloud security-advisories. 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-2021-37631/ (Markdown: https://insights.sbomify.com/CVE-2021-37631/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-37631
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-37631
- OSV: https://osv.dev/vulnerability/CVE-2021-37631

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-37631/
Summaries are generated and may contain mistakes; the official description above is the record.