# CVE-2025-66547: Nextcloud Server users can modify tags on files that do not belong to them

> Non-privileged users can modify tags on files they do not own via bulk tagging, requiring an upgrade to Nextcloud Server.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/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:** Yes
- **Published:** 5 Dec 2025
- **Updated:** 5 Dec 2025
- **Also known as:** BIT-nextcloud-2025-66547, GHSA-hq6c-r898-fgf2

## What is CVE-2025-66547?

CVE-2025-66547 is a medium-severity missing authorization vulnerability in Nextcloud Nextcloud Server, published on 5 Dec 2025. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Nextcloud Server is a self hosted personal cloud system. In Nextcloud Server and Enterprise Server prior to 31.0.1, non-privileged users can modify tags on files they should not have access to via bulk tagging. This vulnerability is fixed in 31.0.1.

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

## Which versions are affected by CVE-2025-66547?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `nextcloud` | Bitnami | All versions | 31.0.1 |

Products: Nextcloud Nextcloud Server.

## How do I fix CVE-2025-66547?

Upgrade nextcloud to 31.0.1 or later.

## Is CVE-2025-66547 being exploited?

There is no known exploitation of CVE-2025-66547 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-2025-66547 and fix it if it is affected.

What it is: CVE-2025-66547 is a medium-severity missing authorization vulnerability in Nextcloud Nextcloud Server, published on 5 Dec 2025. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-66547 in the wild and no public exploit code.

Affected packages and fixed versions:
- nextcloud (Bitnami): affected all versions; fixed in 31.0.1

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-2025-66547/ (Markdown: https://insights.sbomify.com/CVE-2025-66547/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-66547
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-66547
- OSV: https://osv.dev/vulnerability/CVE-2025-66547

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-66547/
Summaries are generated and may contain mistakes; the official description above is the record.