CVE-2025-66514

Nextcloud Mail stored HTML injection in subject text

MEDIUM
5.4
CVSS Score
Published: December 5, 2025 at 05:32 PM UTC
Updated: October 15, 2026 at 09:10 PM UTC
2 products affected across 1 vendorMailsecurity-advisories

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Severity
MEDIUM5.4
Exploit prediction
EPSS 0.3%
SSVC
No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

References (4)

x_refsource_MISCIssue TrackingPatch
Source: cverecord
https://github.com/nextcloud/mail/pull/11740
x_refsource_MISCPermissions RequiredVendor Advisory
Source: cverecord
https://hackerone.com/reports/3357036

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

Attack Vector
NETWORK
Complexity
LOW
Privileges
LOW
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality
LOW
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusANALYZED
CWE
CWE-79

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