Zettlr version 2.3.0 allows an external attacker to remotely obtain arbitrary local files on any client that attempts to view a malicious markdown file through Zettlr. This is possible because the application does not have a CSP policy (or at least not strict enough) and/or does not properly validate the contents of markdown files before rendering them.

No filtering of cross-site scripting (XSS) payloads in the markdown-editor in Zettlr 1.8.7 allows attackers to perform remote code execution via a crafted file.

Cross-site scripting vulnerability in Zettlr from 0.20.0 to 1.8.8 allows an attacker to execute an arbitrary script by loading a file or code snippet containing an invalid iframe into Zettlr.