CVE-2026-66843

Summary

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 Software

Weaknesses

• CWE-829: CWE-829 Inclusion of Functionality from Untrusted Control Sphere

Workarounds

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 <object> from loading, and hosting user uploads on a separate origin removes the escalation path.

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: no
  • Technical Impact: partial

References

• https://github.com/rrrene/html_sanitize_ex/security/advisories/GHSA-xmm9-jc22-rcgj
• https://cna.erlef.org/cves/CVE-2026-66843.html
• https://osv.dev/vulnerability/EEF-CVE-2026-66843
• https://github.com/rrrene/html_sanitize_ex/commit/bec27fec4de99e40c68c4285a610e09e791a3eaf

• ←Previous
• Next→