CVE-2025-64011: Nextcloud Server 30.0.0 is vulnerable to an Insecure Direct Object Reference (IDOR) in the /core/preview endpo

Routine

MEDIUM 4.3DOWNGRADE

CVE-2025-64011 is a medium-severity flaw (CVSS 4.3) affecting nextcloud server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Public exploit reference

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	4.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.3% (top 75%)
CISA exploited list	No
Weakness	CWE-639
Published	2025-12-12
Last modified	2026-10-14

Publisher (CNA): MITRE · Vendor: nextcloud

Last updated 2026-10-14 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-12-12 17:15 UTCPublished CVE record published
2026-10-14 17:10 UTCUpdated Record last modified

nextcloud nextcloud server DOWNGRADE

Affected: 30.0.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 30.0.0

1. Check installed version

apt-cache policy nextcloud-server || rpm -q nextcloud-server || nextcloud-server --version

2. No fixed release: DOWNGRADE to a release before 30.0.0 (Debian / Ubuntu)

apt-cache madison nextcloud-server sudo apt install nextcloud-server=<VERSION_BEFORE_30.0.0> sudo apt-mark hold nextcloud-server

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list nextcloud-server sudo dnf downgrade nextcloud-server-<VERSION_BEFORE_30.0.0> sudo dnf versionlock add nextcloud-server

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-64011?

nextcloud server: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2025-64011 being exploited?

CVE-2025-64011 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-64011 affect?

CVE-2025-64011 affects nextcloud server. Severity is medium (CVSS 4.3). 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.

How urgent is CVE-2025-64011?

Priority 26/100. Public exploit reference

Software pages

Nextcloud vulnerabilities

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References

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