CVE-2026-66843 (GCVE-0-2026-66843)

Vulnerability from cvelistv5 – Published: 2026-08-06 14:48 – Updated: 2026-08-06 15:40
VLAI
Title
html_sanitize_ex HTML5 scrubber keeps attacker-supplied `<object>` elements, allowing untrusted content embedding
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.
Severity
2.3 (Low)
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
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
  • CWE-829 - Inclusion of Functionality from Untrusted Control Sphere
Assigner
EEF
References
Impacted products
Vendor Product Version
rrrene html_sanitize_ex Affected: 0.3.1 , < 1.5.3 (semver)
    cpe:2.3:a:rrrene:html_sanitize_ex:*:*:*:*:*:*:*:*
 Create a notification for this product.
rrrene html_sanitize_ex Affected: 8976d64ea0b77d26093a94a43ec48a3978e8d028 , < bec27fec4de99e40c68c4285a610e09e791a3eaf (git)
    cpe:2.3:a:rrrene:html_sanitize_ex:*:*:*:*:*:*:*:*
 Create a notification for this product.
Credits
Peter Ullrich René Föhring Jonatan Männchen / EEF
Show details on NVD website
To clipboard 

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\u003ccode\u003emarkdown_html/1\u003c/code\u003e or \u003ccode\u003estrip_tags/1\u003c/code\u003e, none of which allow \u003ccode\u003eobject\u003c/code\u003e, or define a custom scrubber that omits it.\u003c/p\u003e\\n\u003cp\u003eA Content-Security-Policy of \u003ccode\u003eobject-src \u0027none\u0027\u003c/code\u003e blocks an injected \u003ccode\u003e\u0026lt;object\u0026gt;\u003c/code\u003e from loading, and hosting user uploads on a separate origin removes the escalation path.\u003c/p\u003e\", \"base64\": false}, {\"type\": \"text/markdown\", \"value\": \"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.\\n\\nA Content-Security-Policy of `object-src \u0027none\u0027` blocks an injected `\u003cobject\u003e` from loading, and hosting user uploads on a separate origin removes the escalation path.\", \"base64\": false}]}], \"descriptions\": [{\"lang\": \"en\", \"value\": \"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 \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 1.5.3.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eInclusion 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 \u003ccode\u003edata\u003c/code\u003e attribute of an \u003ccode\u003e\u0026lt;object\u0026gt;\u003c/code\u003e element in sanitized HTML. \u003ccode\u003eobject\u003c/code\u003e is the one URI-bearing element in \u003ccode\u003elib/html_sanitize_ex/scrubber/html5.ex\u003c/code\u003e never registered through \u003ccode\u003eallow_tag_with_uri_attributes/3\u003c/code\u003e, and its only guard is a prefix match on lowercase \u003ccode\u003e\\\"javascript:\\\"\u003c/code\u003e, so mixed-case variants, \u003ccode\u003edata:\u003c/code\u003e URIs, protocol-relative URLs and same-origin paths all survive.\u003c/p\u003e\\n\u003cp\u003eThis is not unconditional cross-site scripting. A \u003ccode\u003ejavascript:\u003c/code\u003e URL does not execute through \u003ccode\u003e\u0026lt;object data\u0026gt;\u003c/code\u003e in current browsers, \u003ccode\u003edata:\u003c/code\u003e 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.\u003c/p\u003e\\n\u003cp\u003eThis issue affects html_sanitize_ex: from 0.3.1 before 1.5.3.\u003c/p\u003e\", \"base64\": false}, {\"type\": \"text/markdown\", \"value\": \"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 `\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 1.5.3.\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-829\", \"description\": \"CWE-829 Inclusion of Functionality from Untrusted Control Sphere\"}]}], \"configurations\": [{\"lang\": \"en\", \"value\": \"Only 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.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eOnly \u003ccode\u003eHtmlSanitizeEx.html5/1\u003c/code\u003e, and custom scrubbers declared with \u003ccode\u003euse HtmlSanitizeEx, extend: :html5\u003c/code\u003e, allow the \u003ccode\u003eobject\u003c/code\u003e element, and the sanitized output must be rendered to other users.\u003c/p\u003e\\n\u003cp\u003eScript 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 \u003ccode\u003etext/html\u003c/code\u003e.\u003c/p\u003e\", \"base64\": false}, {\"type\": \"text/markdown\", \"value\": \"Only `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`.\", \"base64\": false}]}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:a:rrrene:html_sanitize_ex:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"1.5.3\", \"versionStartIncluding\": \"0.3.1\"}], \"operator\": \"OR\"}], \"operator\": \"AND\"}], \"providerMetadata\": {\"orgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"shortName\": \"EEF\", \"dateUpdated\": \"2026-08-06T14:48:20.513Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-66843\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-06T15:40:50.570Z\", \"dateReserved\": \"2026-08-06T09:00:01.259Z\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"datePublished\": \"2026-08-06T14:48:20.513Z\", \"assignerShortName\": \"EEF\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.