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

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

Which versions are affected by CVE-2025-66547?

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

Products include Nextcloud Nextcloud Server.

How do I fix CVE-2025-66547?

Upgrade nextcloud to 31.0.1 or later.

Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.

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 Preview generation used third-party library not suited for user-generated content in Nextcloud server Critical 9.3
• CVE-2023-26482 Scope of workflow operations is not validated in nextcloud server Critical 9.1
• CVE-2018-3775 Auth bypass in Nextcloud Server High 8.8
• CVE-2023-35172 Nextcloud Server password reset endpoint is not brute force protected High 8.7
• CVE-2023-32320 Nextcloud Server's brute force protection allows someone to send more requests than intended High 8.7

All Nextcloud Nextcloud Server vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BIT-nextcloud-2025-66547, GHSA-hq6c-r898-fgf2.