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TI-2025-40936 Aliases CVE-2025-66514

Nextcloud Mail stored HTML injection in subject text

Priority LOW 24CWE-79Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
Required
Attack complexity
Low
Impact type
Cross-site scripting
Confidentiality · integrity · availability
Low · Low · None
Fix status
Fixed

Attack profile from CVSS 3.1 · NVD. Fix status from CNA. Impact type from CWE-79.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00268 19th percentileScored 2026-11-07
Fix Fixed security-advisories (nextcloud): 5.5.3

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
nextcloudsecurity-advisories5.2.0-beta.1 to before 5.5.35.5.3Patch availableCNA
  • security-advisories Vendornextcloud Affected 5.2.0-beta.1 to before 5.5.3 Fixed in 5.5.3 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:nextcloud:mail:*:*:*:*:*:nextcloud:*:*before 5.5.3Vulnerablenextcloud
  • cpe:2.3:a:nextcloud:mail:*:*:*:*:*:nextcloud:*:* Versions before 5.5.3 Vulnerable ·nextcloud

Remediation

  • Fix · CNA security-advisories (nextcloud) Fixed in 5.5.3

Timeline

  1. 2026-10-02 Threatist record created from CVE-2025-66514

References

Patch 3

Advisory 1

  • TI-2023-09741 Blind SSRF via server URL input in the Nextcloud Mail app CVSS 3.1MEDIUM 5.0
  • TI-2022-13176 Unauthenticated SSRF in 3rd party module "cerdic/csstidy" CVSS 3.1CRITICAL 9.8
  • TI-2023-26170 Nextcloud Mail app vulnerable to Server-Side Request Forgery CVSS 3.1CRITICAL 9.8
  • TI-2021-12320 Missing permission check on email metadata retrieval CVSS 3.1HIGH 8.8
  • TI-2024-35179 Nextcloud Mail auto configurator can be tricked into sending account information to wrong servers CVSS 3.1HIGH 8.2
  • TI-2020-06574 A missing verification of the TLS host in Nextcloud Mail 1.1.3 allowed a man in the middle attack. CVSS 3.1HIGH 7.0
See all 14 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences