# CVE-2023-48239: Nextcloud Server users can make external storage mount points inaccessible for other users

> A malicious user can modify external storage configurations to make them inaccessible to other users, causing denial of service.

- **Severity:** High 8.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:H`)
- **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:** 21 Nov 2023
- **Updated:** 10 Jun 2025
- **Also known as:** GHSA-f962-hw26-g267

## What is CVE-2023-48239?

CVE-2023-48239 is a high-severity missing authorization vulnerability in Nextcloud Nextcloud Server, published on 21 Nov 2023. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Nextcloud Server provides data storage for Nextcloud, an open source cloud platform. Starting in version 25.0.0 and prior to versions 25.0.13, 26.0.8, and 27.1.3 of Nextcloud Server and starting in version 20.0.0 and prior to versions 20.0.14.16, 21.0.9.13, 22.2.10.15, 23.0.12.12, 24.0.12.8, 25.0.13, 26.0.8, and 27.1.3 of Nextcloud Enterprise Server, a malicious user could update any personal or global external storage, making them inaccessible for everyone else as well. Nextcloud Server 25.0.13, 26.0.8, and 27.1.3 and Nextcloud Enterprise Server is upgraded to 20.0.14.16, 21.0.9.13, 22.2.10.15, 23.0.12.12, 24.0.12.8, 25.0.13, 26.0.8, and 27.1.3 contain a patch for this issue. As a workaround, disable app files_external. This workaround also makes the external storage inaccessible but retains the configurations until a patched version has been deployed.

Weakness: CWE-284 (Improper Access Control)

## Which versions are affected by CVE-2023-48239?

It affects 1 product.


Products: Nextcloud Nextcloud Server.

## How do I fix CVE-2023-48239?

No fix has been published for CVE-2023-48239 yet. Limit exposure of the affected software until one is available.

## Is CVE-2023-48239 being exploited?

There is no known exploitation of CVE-2023-48239 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-2023-48239 and fix it if it is affected.

What it is: CVE-2023-48239 is a high-severity missing authorization vulnerability in Nextcloud Nextcloud Server, published on 21 Nov 2023. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-48239 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-2023-48239/ (Markdown: https://insights.sbomify.com/CVE-2023-48239/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-48239
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-48239
- OSV: https://osv.dev/vulnerability/CVE-2023-48239

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-48239/
Summaries are generated and may contain mistakes; the official description above is the record.