CVE-2026-66843
Inclusion of Functionality from Untrusted Control Sphere vulnerability in the HTML5 scrubber in rrrene html_sanitize_ex allows a remote attacker to load a document of their choosing into a trusted page via the data attribute of an <object> element in sanitized HTML. object is the one URI-bearing element in lib/html_sanitize_ex/scrubber/html5.ex never registered through allow_tag_with_uri_attributes/3, and its only guard is a prefix match on lowercase "javascript:", so mixed-case variants, data: URIs, protocol-relative URLs and same-origin paths all survive. This is not unconditional cross-site scripting. A javascript: URL does not execute through <object data> in current browsers, data: documents load in an opaque origin, and host-origin script execution additionally requires the application to serve attacker-controlled content from a same-origin path. This issue affects html_sanitize_ex: from 0.3.1 before 1.5.3.
- Affected products
- Html Sanitize Ex
- Rrrene Htmlsanitizeex
- < 1.5.3
- CVSS 3.1
- 6.1 MEDIUM
- EPSS
- 0.3% (21th percentile)
- Weakness
- CWE-829
- NVD status
- Analyzed
- Published
- 2026-08-06
- Attack patterns
- CAPEC-175
Workaround
Sanitize with basic_html/1, markdown_html/1 or strip_tags/1, none of which allow object, or define a custom scrubber that omits it. A Content-Security-Policy of object-src 'none' blocks an injected from loading, and hosting user uploads on a separate origin removes the escalation path.
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