CVE-2025-64501: Prosemirror to html Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-52c5-vh7f-26fx",
  "modified" : "2026-01-23T21:37:34Z",
  "published" : "2025-11-06T15:44:35Z",
  "aliases" : [ "CVE-2025-64501" ],
  "summary" : "Cross-Site Scripting (XSS) vulnerability through unescaped HTML attribute values",
  "details" : "### Impact\n\nThe 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.\n\n**Who is impacted:**\n- Any application using prosemirror_to_html to convert ProseMirror documents to HTML\n- Applications that process user-generated ProseMirror content are at highest risk\n- End users viewing the rendered HTML output could have malicious JavaScript executed in their browsers\n\n**Attack vectors include:**\n- `href` attributes with `javascript:` protocol: `<a href=\"javascript:alert(document.cookie)\">`\n- Event handlers: `<div onclick=\"maliciousCode()\">`\n- `onerror` attributes on images: `<img src=x onerror=\"alert('XSS')\">`\n- Other HTML attributes that can execute JavaScript\n\n### Patches\n\nA fix is currently in development. Users should upgrade to version **0.2.1** or later once released.\n\nThe patch escapes all HTML attribute values using `CGI.escapeHTML` to prevent injection attacks.\n\n### Workarounds\n\nUntil a patched version is available, users can implement one or more of these mitigations:\n\n1. **Sanitize output**: Pass the HTML output through a sanitization library like [Sanitize](https://github.com/rgrove/sanitize) or [Loofah](https://github.com/flavorjones/loofah):\n```ruby\n   html = ProsemirrorToHtml.render(document)\n   safe_html = Sanitize.fragment(html, Sanitize::Config::RELAXED)\n```\n\n2. **Implement Content Security Policy (CSP)**: Add strict CSP headers to prevent inline JavaScript execution:\n```\n   Content-Security-Policy: default-src 'self'; script-src 'self'\n```\n\n3. **Input validation**: If possible, validate and sanitize ProseMirror documents before conversion to prevent malicious content from entering the system.\n\n### References\n\n- Vulnerable code: https://github.com/etaminstudio/prosemirror_to_html/blob/ea8beb32f6c37f29f042ba4155ccf18504da716e/lib/prosemirror_to_html.rb#L249\n- [OWASP XSS Prevention Cheat Sheet](https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html)\n- [CWE-79: Improper Neutralization of Input During Web Page Generation](https://cwe.mitre.org/data/definitions/79.html)",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "prosemirror_to_html"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.2.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/etaminstudio/prosemirror_to_html/security/advisories/GHSA-52c5-vh7f-26fx"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-64501"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/etaminstudio/prosemirror_to_html/commit/4d59f94f550bcabeec30d298791bbdd883298ad8"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/etaminstudio/prosemirror_to_html"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/etaminstudio/prosemirror_to_html/blob/ea8beb32f6c37f29f042ba4155ccf18504da716e/lib/prosemirror_to_html.rb#L249"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/prosemirror_to_html/CVE-2025-64501.yml"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/prosemirror_to_html/GHSA-vfpf-xmwh-8m65.yml"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-11-06T15:44:35Z",
    "nvd_published_at" : "2025-11-10T22:15:37Z"
  }
}