Summary

rails-html-sanitizer >= 1.0.3, < 1.4.4 is vulnerable to cross-site scripting via data URIs when used in combination with Loofah >= 2.1.0.

Mitigation

Upgrade to rails-html-sanitizer >= 1.4.4.

Severity

The maintainers have evaluated this as Medium Severity 6.1.

References

- CWE - CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (4.9) - SVG MIME Type (image/svg+xml) is misleading to developers · Issue #266 · w3c/svgwg - https://github.com/rails/rails-html-sanitizer/issues/135 - https://hackerone.com/reports/1694173

Credit

This vulnerability was independently reported by Maciej Piechota (@haqpl) and Mrinmoy Das (@goromlagche).

There is a possible XSS vulnerability in all rails-html-sanitizer gem versions below 1.0.4 for Ruby. The gem allows non-whitelisted attributes to be present in sanitized output when input with specially-crafted HTML fragments, and these attributes can lead to an XSS attack on target applications. This issue is similar to CVE-2018-8048 in Loofah. All users running an affected release should either upgrade or use one of the workarounds immediately.