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CVE-2025-66512: Nextcloud Server is a self hosted personal cloud system

24
Routine
MEDIUM 5.4UPGRADE

CVE-2025-66512 is a medium-severity flaw (CVSS 5.4) affecting nextcloud server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Nextcloud Server is a self hosted personal cloud system. In Nextcloud Server and Server Enterprise prior to 31.0.12 and 32.0.3, a missing sanitization allowed malicious users to circumvent the content security policy when a malicious user manages to trick a user it viewing an uploaded SVG outside of the Nextcloud Servers web page.

Why this priority

  • No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score5.4 (Medium)
Attack vectorNetwork (remote)
Attack complexityLow
Privileges neededNone
User interactionRequired
EPSS exploit chance0.3% (top 80%)
CISA exploited listNo
WeaknessCWE-80, CWE-79
Published2025-12-05
Last modified2026-10-18
Publisher (CNA): GitHub, Inc. · Vendor: nextcloud

Share: LinkedIn · X · Reddit

Last updated 2026-10-18 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

nextcloud nextcloud server UPGRADE
Affected: >= 31.0.0 and < 31.0.12 · >= 32.0.0 and < 32.0.3
Fixed in: 31.0.12, 32.0.3
Safe to downgrade to: a release before 31.0.0
1. Check installed version
apt-cache policy nextcloud-server || rpm -q nextcloud-server || nextcloud-server --version
2. UPGRADE to 31.0.12 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade nextcloud-server
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade nextcloud-server
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
3. If no update is available yet, DOWNGRADE to a release before 31.0.0 (Debian / Ubuntu)
apt-cache madison nextcloud-server sudo apt install nextcloud-server=<VERSION_BEFORE_31.0.0> sudo apt-mark hold nextcloud-server
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list nextcloud-server sudo dnf downgrade nextcloud-server-<VERSION_BEFORE_31.0.0> 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-2025-66512?

nextcloud server: upgrade to 31.0.12, 32.0.3. Exact commands for each OS are on this page.

Is CVE-2025-66512 being exploited?

CVE-2025-66512 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-2025-66512 affect?

CVE-2025-66512 affects nextcloud server. Severity is medium (CVSS 5.4). Nextcloud Server is a self hosted personal cloud system. In Nextcloud Server and Server Enterprise prior to 31.0.12 and 32.0.3, a missing sanitization allowed malicious users to circumvent the content security policy when a malicious user m

How urgent is CVE-2025-66512?

Priority 24/100. No elevated risk signals yet.

Software pages

Nextcloud vulnerabilities

Related CVEs

References

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