{"id":"EEF-CVE-2026-66843","summary":"html_sanitize_ex HTML5 scrubber keeps attacker-supplied `\u003cobject\u003e` elements, allowing untrusted content embedding","details":"## Summary\n\nInclusion 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 `\u003cobject\u003e` 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.\n\nThis is not unconditional cross-site scripting. A `javascript:` URL does not execute through `\u003cobject data\u003e` 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.\n\nThis issue affects html_sanitize_ex: from 0.3.1 before 1.4.5 and from 1.5.0-rc.0 before 1.5.3.\n\n## Workarounds\n\nSanitize with `basic_html/1`, `markdown_html/1` or `strip_tags/1`, none of which allow `object`, or define a custom scrubber that omits it.\n\nA Content-Security-Policy of `object-src 'none'` blocks an injected `\u003cobject\u003e` from loading, and hosting user uploads on a separate origin removes the escalation path.\n\n## Configurations\n\nOnly `HtmlSanitizeEx.html5/1`, and custom scrubbers declared with `use HtmlSanitizeEx, extend: :html5`, allow the `object` element, and the sanitized output must be rendered to other users.\n\nScript execution in the host origin additionally requires the application to serve attacker-controlled HTML from a same-origin path, such as an uploads directory served as `text/html`.","aliases":["CVE-2026-66843","GHSA-xmm9-jc22-rcgj"],"modified":"2026-09-08T16:15:02.412999777Z","published":"2026-08-06T14:48:20.513Z","database_specific":{"cpe_ids":["cpe:2.3:a:rrrene:html_sanitize_ex:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-829"],"capec_ids":["CAPEC-175"]},"references":[{"type":"ADVISORY","url":"https://github.com/rrrene/html_sanitize_ex/security/advisories/GHSA-xmm9-jc22-rcgj"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-66843.html"},{"type":"FIX","url":"https://github.com/rrrene/html_sanitize_ex/commit/bec27fec4de99e40c68c4285a610e09e791a3eaf"},{"type":"FIX","url":"https://github.com/rrrene/html_sanitize_ex/commit/ce038aa1af5a960d50f8eb5d368cc57bb2b9a9f0"},{"type":"PACKAGE","url":"https://hex.pm/packages/html_sanitize_ex"}],"affected":[{"package":{"name":"html_sanitize_ex","ecosystem":"Hex","purl":"pkg:hex/html_sanitize_ex"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0.3.1"},{"fixed":"1.4.5"}]},{"type":"SEMVER","events":[{"introduced":"1.5.0-rc.0"},{"fixed":"1.5.3"}]}],"versions":["0.3.1","1.0.0","1.0.1","1.1.0","1.1.0-rc1","1.1.1","1.2.0","1.3.0","1.3.0-rc1","1.3.0-rc2","1.3.0-rc3","1.4.0","1.4.1","1.4.2","1.4.3","1.4.4","1.4.4-rc.0","1.5.0","1.5.0-rc.0","1.5.1","1.5.2"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-66843.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/rrrene/html_sanitize_ex","events":[{"introduced":"8976d64ea0b77d26093a94a43ec48a3978e8d028"},{"fixed":"bec27fec4de99e40c68c4285a610e09e791a3eaf"},{"fixed":"ce038aa1af5a960d50f8eb5d368cc57bb2b9a9f0"}]}],"versions":["v1.4.4","v1.5.2","v1.5.1","v1.5.0","v1.5.0-rc.0","v1.4.3","v1.4.2","v1.4.1","v1.2.0","v1.0.1","v1.0.0","v0.3.1"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-66843.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N"}],"credits":[{"name":"Peter Ullrich","type":"FINDER"},{"name":"René Föhring","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"ANALYST"}]}