BaseFortify

Publication date: 2025-12-05

Last updated on: 2025-12-09

Assigner: GitHub, Inc.

Description

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.

CVSS Scores

EPSS Scores

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Meta Information

Published

2025-12-05

Last Modified

2025-12-09

Generated

2026-07-06

AI Q&A

2025-12-05

EPSS Evaluated

2026-07-05

NVD

CVE-2025-66514

Affected Vendors & Products

Vendor	Product	Version / Range
nextcloud	mail	to 5.5.3 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-79	The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

Attack-Flow Graph

Executive Summary

This vulnerability is a stored HTML injection in the Nextcloud Mail app's message list that allows an authenticated user to inject HTML into email subjects. Although JavaScript execution is blocked by the content security policy, the injected HTML could still affect how email subjects are displayed.

Impact Analysis

The vulnerability could allow an authenticated user to inject HTML into email subjects, potentially leading to misleading or manipulated email displays. However, since JavaScript is blocked, the risk of more severe attacks like cross-site scripting is reduced. The impact is limited to integrity issues without confidentiality or availability impact.

Mitigation Strategies

Upgrade the Nextcloud Mail app to version 5.5.3 or later to fix the stored HTML injection vulnerability.

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