EEF-CVE-2026-66829

## Summary

URL Redirection to Untrusted Site ('Open Redirect') vulnerability in the HTML5 scrubber in rrrene html_sanitize_ex allows a remote attacker to force visitors of a page to navigate to a site of the attacker's choosing via a `<meta http-equiv="refresh">` element in sanitized HTML. `HtmlSanitizeEx.html5/1` keeps attacker-supplied `<meta>` elements in its output. A `meta` element acts on the whole document rather than on the fragment it was embedded in, so it can also declare document-wide directives such as `Content-Security-Policy`.

This is not cross-site scripting. Browsers do not navigate a meta refresh to a `javascript:` URL, so the uppercase `JAVASCRIPT:` filter bypass yields no script execution and none was demonstrated.

This issue affects html_sanitize_ex: from 0.3.1 before 1.4.5 and from 1.5.0-rc.0 before 1.5.3.

## Workarounds

Sanitize with `basic_html/1`, `markdown_html/1` or `strip_tags/1`, none of which allow `meta`, or define a custom scrubber that omits it.

## Configurations

Only `HtmlSanitizeEx.html5/1`, and custom scrubbers declared with `use HtmlSanitizeEx, extend: :html5`, allow the `meta` element, and the sanitized output must be rendered to other users.