Joplin is a free, open source note taking and to-do application. Joplin fails to take into account that "<" followed by a non letter character will not be considered html. As such it is possible to do an XSS by putting an "illegal" tag within a tag.

Joplin is a free, open source note taking and to-do application. A Cross site scripting (XSS) vulnerability in affected versions allows clicking on an untrusted image link to execute arbitrary shell commands. The HTML sanitizer (`packages/renderer/htmlUtils.ts::sanitizeHtml`) preserves `<map>` `<area>` links. However, unlike `<a>` links, the `target` and `href` attributes are not removed. Additionally, because the note preview pane isn't sandboxed to prevent top navigation, links with `target` set to `_top` can replace the toplevel electron page. Because any toplevel electron page, with Joplin's setup, has access to `require` and can require node libraries, a malicious replacement toplevel page can import `child_process` and execute arbitrary shell commands. This issue has been fixed in commit 7c52c3e9a81a52ef1b42a951f9deb9d378d59b0f which is included in release version 2.12.8. Users are advised to upgrade. There are no known workarounds for this vulnerability.

Joplin before 2.11.5 allows XSS via an AREA element of an image map.

Joplin before 2.11.5 allows XSS via a USE element in an SVG document.

Cross Site Scripting vulnerability in Joplin Desktop App before v2.9.17 allows attacker to execute arbitrary code via improper santization.

Cross Site Scripting (XSS) vulnerability in Joplin Desktop App before 1.8.5 allows attackers to execute aribrary code due to improper sanitizing of html.

Joplin 2.6.10 allows remote attackers to execute system commands through malicious code in user search results.

Joplin before 2.0.9 allows XSS via button and form in the note body.

Joplin 1.2.6 for Desktop allows XSS via a LINK element in a note.

An XSS issue in Joplin desktop 1.0.190 to 1.0.245 allows arbitrary code execution via a malicious HTML embed tag.