# CVE-2021-32727: End-to-end encryption device setup did not verify public key

> Attackers can bypass end-to-end encryption verification to access encrypted data if a malicious public key is served by the Nextcloud instance.

- **Severity:** Medium 5.7 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/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:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 12 Jul 2021
- **Updated:** 3 Aug 2024
- **Also known as:** BIT-nextcloud-2021-32727, GHSA-5v33-r9cm-7736

## What is CVE-2021-32727?

CVE-2021-32727 is a medium-severity vulnerability in nextcloud security-advisories, published on 12 Jul 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

Nextcloud Android Client is the Android client for Nextcloud. Clients using the Nextcloud end-to-end encryption feature download the public and private key via an API endpoint. In versions prior to 3.16.1, the Nextcloud Android client skipped a step that involved the client checking if a private key belonged to a previously downloaded public certificate. If the Nextcloud instance served a malicious public key, the data would be encrypted for this key and thus could be accessible to a malicious actor. The vulnerability is patched in version 3.16.1. As a workaround, do not add additional end-to-end encrypted devices to a user account.

Weakness: CWE-295 (Improper Certificate Validation)

## Which versions are affected by CVE-2021-32727?

1 open source package ship an affected version, including nextcloud. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `nextcloud` | Bitnami | All versions | 3.16.1 |

Products: Nextcloud Nextcloud.

## How do I fix CVE-2021-32727?

Upgrade nextcloud to 3.16.1 or later.

## Is CVE-2021-32727 being exploited?

There is no known exploitation of CVE-2021-32727 in the wild and no public exploit code.

## Other vulnerabilities in nextcloud security-advisories

- [CVE-2019-5454](https://insights.sbomify.com/CVE-2019-5454/): SQL injection in com.nextcloud.client (critical 9.8)
- [CVE-2021-43863](https://insights.sbomify.com/CVE-2021-43863/): SQL Injection in FileContentProvider (GHSL-2021-1007) (high 7.5)
- [CVE-2019-5450](https://insights.sbomify.com/CVE-2019-5450/): Cross-site scripting in com.nextcloud.client (medium 6.8)
- [CVE-2019-5455](https://insights.sbomify.com/CVE-2019-5455/): Auth bypass in com.nextcloud.client (medium 6.8)
- [CVE-2021-22905](https://insights.sbomify.com/CVE-2021-22905/): Information disclosure in Nextcloud Android App (com.nextcloud.client) (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-32727 and fix it if it is affected.

What it is: CVE-2021-32727 is a medium-severity vulnerability in nextcloud security-advisories, published on 12 Jul 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-32727 in the wild and no public exploit code.

Affected packages and fixed versions:
- nextcloud (Bitnami): affected all versions; fixed in 3.16.1

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-2021-32727/ (Markdown: https://insights.sbomify.com/CVE-2021-32727/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-32727
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-32727
- OSV: https://osv.dev/vulnerability/CVE-2021-32727

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-32727/
Summaries are generated and may contain mistakes; the official description above is the record.