NVD / CVE Program· CNA GitHub_M

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

Noroxi assessment

Priority: Monitor (action score 17/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.27% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
Fixed version: nextcloud security-advisories 31.0.1.

Low priority for now. Upgrade to nextcloud security-advisories 31.0.1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

MediumCVSS 4.3 · v3.1—No exploit Fix available

Broken access control (IDOR)

BDU:2026-03382

Published: Dec 5, 2025
Updated: Oct 18, 2026
EPSS: 0.2% · 20th percentile
CWE: CWE-639

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 17 / 40 · 4.3 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.2%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · GitHub_M: 4.3; NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
nextcloud	nextcloud server	cpe:2.3:a:nextcloud:nextcloud_server

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

nextcloud nextcloud server31.0.0 and later · before 31.0.1

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

nextcloud security-advisories
- < 31.0.1affected

Same product

nextcloud: all records

Other highest-scoring records for the same primary product.

CVE-2023-26482Scope of workflow operations is not validated in nextcloud server
40Plan
CVE-2021-32802Preview generation used third-party library not suited for user-generated content in Nextcloud server
40Plan
CVE-2021-32726Webauthn tokens not removed after user has been deleted
40Plan

Published before and after this one in the same product

← EarlierCVE-2025-66510Dec 5, 2025 · Nextcloud Server Contacts Search allowed users to retrieve contact information of other users beyond their contact list
19Monitor
← EarlierCVE-2025-66512Dec 5, 2025 · Nextcloud Server vulnerable to XSS in SVG images when opened outside of Nextcloud
24Monitor
Later →CVE-2025-66552Dec 5, 2025 · Nextcloud Server admin_audit does not log all actions on files in groupfolders
17Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
nextcloud security-advisories	31.0.1 · description	Vendor (CNA)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

CVE-2026-45281178 days apartNextcloud: Cross-Account Calendar Takeover via Unauthorized Group-Member-Set Update
32Monitor
CVE-2026-45810178 days apartNextcloud: Propfind requests for file comments allowed to load comments for other files
27Monitor
CVE-2025-640117 days apartNextcloud Server 30.0.0 is vulnerable to an Insecure Direct Object Reference (IDOR) in the /core/preview endpoint.
17Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

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Bug bounty scope

NextcloudHackerOne · paid

The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
A low-privileged account is enough.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: low · data or configuration can be modified
Availability: none

Attack vector: Network
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: Low
Availability impact: None

Weakness class (CWE)

CWE-639 · Authorization Bypass Through User-Controlled Key

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

nvd-secondary

Root cause

The endpoint fetches the record by the ID sent in the request, but never checks whether the record belongs to the requesting user.

The bug in code

The whole CWE-639 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1const invoice = await Invoice.findById(req.params.id);
2res.json(invoice);

Fixed

1const invoice = await Invoice.findOne({
2  id: req.params.id,
3  ownerId: req.user.id,
4});
5if (!invoice) return res.sendStatus(404);
6res.json(invoice);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

Fix✗ → ✓Sep 29, 2026, 11:53 AM UTC

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References

github.com/nextcloud/security-advisories/security/advisories/GHSA-hq6c-r898-fgf2

Show all references (4 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records