CVE-2026-55105

Joplin: Fountain embeds allow arbitrary script execution in published notes and the note viewer

Published 21 Sep 2026 • Updated 21 Sep 2026

Severity: HIGH

Description

Joplin is an open source note-taking and to-do application that organises notes and lists into notebooks. Prior to 3.6.15 and 3.7.2, packages/renderer/MdToHtml/rules/fountain.ts passes HTML generated by the vendored fountain.js renderer into note output without sanitizing it. A malicious Fountain code block can therefore execute script when Fountain rendering is enabled in desktop or mobile clients, or when a note is published through Joplin Server where Fountain rendering is enabled by default. The script can read content subsequently loaded in the reused note viewer or, when published notes are served from the same domain as server content, access data available to an authenticated browser in the server origin. This issue is fixed in versions 3.6.15 and 3.7.2.

Affected products (1)

• laurent22 joplin

Problem types

• CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

References (3)

• https://github.com/laurent22/joplin/security/advisories/GHSA-f7q3-3grx-6wg9
• https://github.com/laurent22/joplin/pull/15659
• https://github.com/laurent22/joplin/commit/8e0812de9d79d1f0698bb76a8c5d7e991df9748d