PT-2025-47871 · Rubygems · Prosemirror To Html

Published 2025-11-13 · Updated 2025-11-13

OSV

CVSS v4.0

8.7

High

Base vector

AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N

Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-52c5-vh7f-26fx.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:

1. 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)

2. Implement Content Security Policy (CSP): Add strict CSP headers to prevent inline JavaScript execution:

  Content-Security-Policy: default-src 'self'; script-src 'self'

3. Input validation: If possible, validate and sanitize ProseMirror documents before conversion to prevent malicious content from entering the system.

References

• Vulnerable code: https://github.com/etaminstudio/prosemirror to html/blob/ea8beb32f6c37f29f042ba4155ccf18504da716e/lib/prosemirror to html.rb#L249
• [OWASP XSS Prevention Cheat Sheet](https://cheatsheetseries.owasp.org/cheatsheets/Cross Site Scripting Prevention Cheat Sheet.html)

Fix

XSS

Weakness Enumeration

CWE-79

Related Identifiers

GHSA-4249-GJR8-JPQ3

Affected Products

Prosemirror To Html

References · 7

• https://osv.dev/vulnerability/GHSA-4249-gjr8-jpq3 · Vendor Advisory
• https://github.com/rubysec/ruby-advisory-db/blob/master/gems/prosemirror_to_html/GHSA-vfpf-xmwh-8m65.yml · Note
• https://github.com/etaminstudio/prosemirror_to_html/blob/ea8beb32f6c37f29f042ba4155ccf18504da716e/lib/prosemirror_to_html.rb#L249 · Note
• https://github.com/etaminstudio/prosemirror_to_html · Note
• https://github.com/etaminstudio/prosemirror_to_html/commit/4d59f94f550bcabeec30d298791bbdd883298ad8 · Note
• https://github.com/etaminstudio/prosemirror_to_html/security/advisories/GHSA-52c5-vh7f-26fx · Note
• https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html · Note