CVE-2025-66514

low-risk
Published 2025-12-05

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.

Do I need to act?

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0.03% chance of exploitation
EPSS score — low exploit probability
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Not on CISA KEV list
No confirmed active exploitation reported to CISA
?
Patch status unknown
Check vendor advisories for fix availability and mitigation guidance
3
CVSS 3.5/10 Low
NETWORK / LOW complexity

Affected Products (1)

Mail

Affected Vendors

Nextcloud

References (4)

Patch https://github.com/nextcloud/mail/commit/c64fcc3b79e0c089b5e1d2e04a07bfa740b2ac0...
Issue Tracking https://github.com/nextcloud/mail/pull/11740
Patch https://github.com/nextcloud/security-advisories/security/advisories/GHSA-v394-8...
Permissions Required https://hackerone.com/reports/3357036
21
/ 100
low-risk
Severity 16/34 · Moderate
Exploitability 0/34 · Minimal
Exposure 5/34 · Minimal