Joplin is an open source note-taking and to-do application that organises notes and lists into notebooks. Versions 3.6.14 and prior contain a Denial of Service (DoS) vulnerability in the title input functionality due to a lack of proper length validation. This flaw allows an attacker to cause an Out Of Memory (OOM) error and subsequent program termination by inserting an excessively long string into a note's title.

This can be triggered either through direct user interface (UI) input or programmatically via the local web service API after compromising an authentication token. There are 2 primary methods of exploitation: via User Interface (UI) Input, and the Local Web Service API. A local user can directly type or paste an extremely long string into the title field when creating or editing a note Joplin runs a local web service (typically on port 41184) that allows programmatic interaction, such as creating or editing notes via HTTP API calls.

If an attacker manages to exfiltrate or compromise the user's authentication token (e.g., through malware on the local system, or other local vulnerabilities), they can then send a crafted HTTP POST request to this local API. By including an excessively long string in the title parameter of this request, the application will attempt to allocate an unbounded amount of memory. This issue has been patched in version 3.7.1.