CVE-2023-39955: Notes attachment render HTML in preview mode

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-08-10 · updated 2026-06-17
Weakness: CWE-79

Description

Notes is a note-taking app for Nextcloud, an open-source cloud platform. Starting in version 4.4.0 and prior to version 4.8.0, when creating a note file with HTML, the content is rendered in the preview instead of the file being offered to download. Nextcloud Notes app version 4.8.0 contains a patch for the issue. No known workarounds are available.

Affected products

nextcloud Notes: from 4.4.0 before 4.8.0 — fixed in 4.8.0

How to fix

Upgrade to a fixed version: nextcloud Notes 4.8.0. Check the vendor advisory for mitigations.

References

https://github.com/nextcloud/notes/pull/1031
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-6g88-37x7-4vw6
https://hackerone.com/reports/1924355
https://github.com/nextcloud/notes/pull/1031
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-6g88-37x7-4vw6
https://hackerone.com/reports/1924355

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