# CVE-2021-32656: Trusted servers exchange can be triggered by attacker

> An attacker can access basic user information via a public link if automatic trusted server addition is enabled in Nextcloud.

- **Severity:** High 8.6 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/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:** 1 Jun 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-j875-vr2q-h6x6

## What is CVE-2021-32656?

CVE-2021-32656 is a high-severity vulnerability in Nextcloud Nextcloud Server, published on 1 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Nextcloud Server is a Nextcloud package that handles data storage. A vulnerability in federated share exists in versions prior to 19.0.11, 20.0.10, and 21.0.2. An attacker can gain access to basic information about users of a server by accessing a public link that a legitimate server user added as a federated share. This happens because Nextcloud supports sharing registered users with other Nextcloud servers, which can be done automatically when selecting the "Add server automatically once a federated share was created successfully" setting. The vulnerability is patched in versions 19.0.11, 20.0.10, and 21.0.2 As a workaround, disable "Add server automatically once a federated share was created successfully" in the Nextcloud settings.

Weakness: CWE-284 (Improper Access Control)

## Which versions are affected by CVE-2021-32656?

It affects 1 product.


Products: Nextcloud Nextcloud Server.

## How do I fix CVE-2021-32656?

No fix has been published for CVE-2021-32656 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-32656 being exploited?

There is no known exploitation of CVE-2021-32656 in the wild and no public exploit code.

## Other vulnerabilities in Nextcloud Nextcloud Server

- [CVE-2021-32802](https://insights.sbomify.com/CVE-2021-32802/): Preview generation used third-party library not suited for user-generated content in Nextcloud server (critical 9.3)
- [CVE-2023-26482](https://insights.sbomify.com/CVE-2023-26482/): Scope of workflow operations is not validated in nextcloud server (critical 9.1)
- [CVE-2018-3775](https://insights.sbomify.com/CVE-2018-3775/): Auth bypass in Nextcloud Server (high 8.8)
- [CVE-2023-35172](https://insights.sbomify.com/CVE-2023-35172/): Nextcloud Server password reset endpoint is not brute force protected (high 8.7)
- [CVE-2023-32320](https://insights.sbomify.com/CVE-2023-32320/): Nextcloud Server's brute force protection allows someone to send more requests than intended (high 8.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-32656 and fix it if it is affected.

What it is: CVE-2021-32656 is a high-severity vulnerability in Nextcloud Nextcloud Server, published on 1 Jun 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-2021-32656 in the wild and no public exploit code.

Affected product: Nextcloud Nextcloud Server. 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-2021-32656/ (Markdown: https://insights.sbomify.com/CVE-2021-32656/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-32656
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-32656
- OSV: https://osv.dev/vulnerability/CVE-2021-32656

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-32656/
Summaries are generated and may contain mistakes; the official description above is the record.