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 products
nextcloud: mail
References4
- github.com/nextcloud/security-advisories/security/advisories/GH… PatchVendor Advisory
- hackerone.com/reports/3357036 Permissions RequiredVendor Advisory
- github.com/nextcloud/mail/commit/c64fcc3b79e0c089b5e1d2e04a07bf… Patch
- github.com/nextcloud/mail/pull/11740 Issue TrackingPatch
Metrics
- CVSS 3.1
-
5.4
MEDIUM
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N - EPSS — exploit probability
- 0% percentile: 19 · as of 11 November 2026
- CWE
- CWE-79
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.