CVE-2025-64501 is a high-severity (CVSS 7.6) Cross-site Scripting (XSS) vulnerability in prosemirror_to_html. A fix is available for prosemirror_to_html — see the affected versions and patch details below.
ProsemirrorToHtml: Cross-Site Scripting vulnerability through unescaped HTML attribute values
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-64501.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2025-64501 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
prosemirror_to_htmlReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
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:
hrefattributes withjavascript:protocol:<a href="javascript:alert(document.cookie)">- Event handlers:
<div onclick="maliciousCode()"> onerrorattributes 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:
html = ProsemirrorToHtml.render(document)
safe_html = Sanitize.fragment(html, Sanitize::Config::RELAXED)
- Implement Content Security Policy (CSP): Add strict CSP headers to prevent inline JavaScript execution:
Content-Security-Policy: default-src 'self'; script-src 'self'
- Input validation: If possible, validate and sanitize ProseMirror documents before conversion to prevent malicious content from entering the system.
References
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | prosemirror_to_html | all versions | 0.2.1bundle update prosemirror_to_html --conservative |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for prosemirror_to_html, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update prosemirror_to_html to 0.2.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-64501 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-64501 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-64501. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-64501 in your dependencies?
O3 Security finds CVE-2025-64501 across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.