CVE-2025-66514: Nextcloud Mail is the mail app for Nextcloud, a self-hosted productivity platform

Q: How do I fix CVE-2025-66514?

mail: upgrade to 5.5.3. Exact commands for each OS are on this page.

Q: Is CVE-2025-66514 being exploited?

CVE-2025-66514 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2025-66514 affect?

CVE-2025-66514 affects mail. Severity is low (CVSS 3.5). Nextcloud Mail is the mail app for Nextcloud, a self-hosted productivity platform. Prior to 5.5.3, a stored HTML injection in the Mail app's message list allowed an authenticated user to inject HTML into the email subjects. Javascript was c

Q: How urgent is CVE-2025-66514?

Priority 16/100. No elevated risk signals yet.

Routine

LOW 3.5UPGRADE

CVE-2025-66514 is a low-severity flaw (CVSS 3.5) affecting mail. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Nextcloud Mail is the mail app for Nextcloud, a self-hosted productivity platform. Prior to 5.5.3, a stored HTML injection in the Mail app's message list allowed an authenticated user to inject HTML into the email subjects. Javascript was correctly blocked by the content security policy of the Nextcloud Server code.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	3.5 (Low)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	Required
EPSS exploit chance	0.2% (top 84%)
CISA exploited list	No
Weakness	CWE-79
Published	2025-12-05
Last modified	2026-10-15

Publisher (CNA): GitHub, Inc. · Vendor: nextcloud

Last updated 2026-10-15 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-12-05 18:15 UTCPublished CVE record published
2026-10-15 21:10 UTCUpdated Record last modified

nextcloud mail UPGRADE

Affected: < 5.5.3

Fixed in: 5.5.3

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy mail || rpm -q mail || mail --version

2. UPGRADE to 5.5.3 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade mail

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mail

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

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-2025-66514?

mail: upgrade to 5.5.3. Exact commands for each OS are on this page.

Is CVE-2025-66514 being exploited?

CVE-2025-66514 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-2025-66514 affect?

CVE-2025-66514 affects mail. Severity is low (CVSS 3.5). Nextcloud Mail is the mail app for Nextcloud, a self-hosted productivity platform. Prior to 5.5.3, a stored HTML injection in the Mail app's message list allowed an authenticated user to inject HTML into the email subjects. Javascript was c

How urgent is CVE-2025-66514?

Priority 16/100. No elevated risk signals yet.

Software pages

Nextcloud vulnerabilities

Related CVEs

CVE-2024-52509 LOW 3.5 UPGRADE Nextcloud Mail is the mail app for Nextcloud, a self-hosted productivity platform
CVE-2024-52508 HIGH 8.2 UPGRADE Nextcloud Mail is the mail app for Nextcloud, a self-hosted productivity platform
CVE-2023-48307 LOW 3.5 UPGRADE Nextcloud Mail is the mail app for Nextcloud, a self-hosted productivity platform
CVE-2023-45660 MEDIUM 4.3 UPGRADE Nextcloud mail is an email app for the Nextcloud home server platform
CVE-2023-33184 LOW 3.5 UPGRADE Nextcloud Mail is a mail app in Nextcloud

References

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