CVE-2026-55105: Joplin: Fountain embeds allow arbitrary script execution in published notes and the note viewer
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 Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Joplinto a version that resolves this vulnerability.Fixed in 3.6.15 - Upgrade
Upgrade
Joplinto a version that resolves this vulnerability.Fixed in 3.7.2
Event History
Frequently Asked Questions
Which deployments are exposed by default?
Joplin Server instances that publish notes are exposed when Fountain rendering is enabled, because it is enabled by default there. Desktop and mobile clients are affected only when Fountain rendering is enabled.
What must an attacker do to exploit this issue?
An attacker needs to provide a note containing a malicious Fountain code block that is rendered by an affected client or published by an affected Joplin Server. No user interaction is required after the vulnerable content is rendered.
What can the injected script access?
The script can read content subsequently loaded in the reused note viewer. For published notes served from the same domain as server content, it may also access data available to an authenticated browser on the server origin.
How can exposure be reduced before upgrading?
Disable Fountain rendering where possible, particularly for published notes and affected desktop or mobile clients. Upgrade to Joplin 3.6.15 or 3.7.2 to apply the fix.