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Vulnerabilities

Vulnerability · CVE-2025-66514

Nextcloud Mail is the mail app for Nextcloud, a self-hosted productivity platform.

Published Dec 5, 2025 · catalog updated Oct 15, 2026 · nextcloud mail

Severity
Medium5.4
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.3%
Remediation
Advisory link
Affected products
cpe nextcloud/mail

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.

Technical analysis

Mechanism and impact are interpreted from ingested advisories — not independent exploit research.

  • CWE classification

    Cross-site Scripting (XSS)

  • Prerequisites and impact

    Follow the original vendor advisory for access prerequisites and impact. This catalog does not invent exploit conditions.

How to fix CVE-2025-66514

Grounded briefings

Catalog interpretations for three audiences. Each brief cites ingested metadata and the original advisories below. They are not independent research and they do not invent exploit steps.

Executive

CVE-2025-66514 is a medium public vulnerability record for nextcloud mail. It is not currently listed in the CISA Known Exploited catalog. Check the linked vendor or CERT advisories for patch status. This summary is a catalog interpretation of the ingested metadata and cites the original advisories below.

System administrator

Identify whether nextcloud mail is in your estate, then compare installed versions with the affected ranges. Affected packages or ranges on record: nextcloud/mail. Check the linked vendor or CERT advisories for patch status. Prefer the vendor or distribution advisory linked in Sources before changing production systems. This is a catalog interpretation, not a runbook.

Security analyst

Signals on file: CVSS 5.4 (technical impact); EPSS 0.3% (30-day exploitation probability). It is not currently listed in the CISA Known Exploited catalog. Weakness classes: CWE-79. Sources contributing to this record: cve_org, epss, nvd. Public exploit references, when present, are outbound links only and are not proof of active exploitation. This is a catalog interpretation of stored metadata.

Related intelligence

  • Exploitation evidence

    Not listed as known exploited in CISA KEV. Not in CISA KEV or VulnCheck KEV.

  • Safe detection guidance

    Compare installed versions with the affected ranges below and verify the advisory from the original publisher. This site stores metadata and outbound links only; it does not ship exploit code or proof-of-concept payloads.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Dec 5, 2025 · NIST NVD

    Detected

    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.

  2. Oct 15, 2026 · NIST NVD

    Updated

    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.

Affected versions

Enter an installed version to get a verified affected / not-affected result against the ranges below.

  • cpe nextcloud/mailversion unspecified

Sources

  • CVE.orgVulnerability recordCVE-2025-66514

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2025-66514

    30-day exploitation probability 0.3%

    first.org
  • NIST NVDVulnerability recordCVE-2025-66514

    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

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.