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GHSA-vfpf-xmwh-8m65

HighCVSS 7.6 / 10
Published Nov 7, 2025·Last modified Nov 10, 2025
Affected Components(0)

No affected components available

Description

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This advisory has been withdrawn because it is a duplicate of GHSA-52c5-vh7f-26fx.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)
  1. Implement Content Security Policy (CSP): Add strict CSP headers to prevent inline JavaScript execution:
   Content-Security-Policy: default-src 'self'; script-src 'self'
  1. 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
Risk Scores
Base Score
7.6

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs basic access or low-level privileges. The attacker needs the user to perform some action, like clicking a link. The vulnerability can affect other systems as well, not just the initial system. There is a high impact on the confidentiality of the information. There is a low impact on the integrity of the data.

Threat Intelligence
7.0

Exploitation activity has been observed. Apply available patches or mitigations urgently.

EPSS
N/A

Probability that this vulnerability will be exploited in the wild within the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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High severity
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