CVE-2025-64011
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-12-12

Last updated on: 2025-12-19

Assigner: MITRE

Description
Nextcloud Server 30.0.0 is vulnerable to an Insecure Direct Object Reference (IDOR) in the /core/preview endpoint. Any authenticated user can access previews of arbitrary files belonging to other users by manipulating the fileId parameter. This allows unauthorized disclosure of sensitive data, such as text files or images, without prior sharing permissions.
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Meta Information
Published
2025-12-12
Last Modified
2025-12-19
Generated
2026-06-16
AI Q&A
2025-12-12
EPSS Evaluated
2026-06-15
NVD
CVE-2025-64011
EUVD
EUVD-2025-203106
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
nextcloud nextcloud_server 30.0.0
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-639 The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.
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Executive Summary

This vulnerability is an Insecure Direct Object Reference (IDOR) in Nextcloud Server 30.0.0 at the /core/preview endpoint. It allows any authenticated user to access previews of arbitrary files belonging to other users by manipulating the fileId parameter, bypassing sharing permissions.

Impact Analysis

The vulnerability can lead to unauthorized disclosure of sensitive data, such as text files or images, because users can view files they do not have permission to access.

Detection Guidance

To detect this vulnerability, monitor authenticated requests to the /core/preview endpoint and check for unusual manipulation of the fileId parameter that accesses files not belonging to the authenticated user. You can use web server logs or proxy tools to identify such requests. For example, using curl to test access: curl -u user:password 'https://your-nextcloud-server/core/preview?fileId=some_id' and verify if files from other users are accessible. Additionally, review access logs for suspicious patterns of fileId parameter usage. [2]

Mitigation Strategies

The immediate mitigation step is to upgrade Nextcloud Server from version 30.0.0 to a fixed version, such as 31.0.9.1 or later, where this vulnerability has been addressed. Until the upgrade is applied, restrict access to the /core/preview endpoint to trusted users only and monitor for suspicious activity involving the fileId parameter. [2]

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