This advisory has been withdrawn because it is a duplicate of GHSA-52c5-vh7f-26fx. This link is maintained to preserve external references.
Original Description
Impact
The prosemirror_to_html gem is vulnerable to Cross-Site Scripting (XSS) attacks through malicious HTML attribute values. While tag content is properly escaped, attribute values are not, allowing attackers to inject arbitrary JavaScript code.
Who is impacted:
Any application using prosemirror_to_html to convert ProseMirror documents to HTML
Applications that process user-generated ProseMirror content are at highest risk
End users viewing the rendered HTML output could have malicious JavaScript executed in their browsers
Attack vectors include:
href attributes with javascript: protocol:
<a href="javascript:alert(document.cookie)">
Event handlers: <div onclick="maliciousCode()">
onerror attributes on images: <img src=x onerror="alert('XSS')">
Other HTML attributes that can execute JavaScript
Patches
A fix is currently in development. Users should upgrade to version 0.2.1 or later once released. The patch escapes all HTML attribute values using CGI.escapeHTML to prevent injection attacks.
Workarounds
Until a patched version is available, users can implement one or more of these mitigations:
Sanitize output: Pass the HTML output through a sanitization
library like Sanitize or
Loofah:
html = ProsemirrorToHtml.render(document)
safe_html = Sanitize.fragment(html, Sanitize::Config::RELAXED)