CVE-2026-66370 (GCVE-0-2026-66370)

Vulnerability from cvelistv5 – Published: 2026-08-06 14:49 – Updated: 2026-08-06 15:42
VLAI
Title
html_sanitize_ex HTML5 scrubber keeps attacker-supplied form-association attributes, allowing form hijacking
Summary
URL Redirection to Untrusted Site ('Open Redirect') vulnerability in the HTML5 scrubber in rrrene html_sanitize_ex allows an unauthenticated remote attacker to retarget a form already on the rendering page and receive whatever the victim submits, including credentials, via the form and formaction attributes on an <input> element in sanitized HTML. HTML's form attribute associates an input with any form on the page by its id even when the input sits outside that form, and formaction on a submit control overrides the owning form's action. Neither attribute receives a scheme check, so an absolute cross-origin URL survives sanitizing. No script executes. The scrubber allows neither form nor button, so the attacker cannot introduce a form of their own and the rendering page must already contain a form carrying an id. This issue affects html_sanitize_ex: from 0.3.1 before 1.5.3.
Severity
4.8 (Medium)
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
  • CWE-601 - URL Redirection to Untrusted Site ('Open Redirect')
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 , < a1e804ed997e780ea71d14393cf2f701330553a6 (git)
    cpe:2.3:a:rrrene:html_sanitize_ex:*:*:*:*:*:*:*:*
 Create a notification for this product.
Credits
Peter Ullrich Jonatan Männchen / EEF René Föhring
Show details on NVD website
To clipboard 

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                "id": "CVE-2026-66370",
                "options": [
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                    "Exploitation": "none"
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                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-08-06T15:42:03.803831Z",
                "version": "2.0.3"
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          "dateUpdated": "2026-08-06T15:42:09.603Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
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        "title": "CISA ADP Vulnrichment"
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          "collectionURL": "https://repo.hex.pm",
          "cpes": [
            "cpe:2.3:a:rrrene:html_sanitize_ex:*:*:*:*:*:*:*:*"
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              "name": "\u0027Elixir.HtmlSanitizeEx.Scrubber.HTML5\u0027:scrub_attribute/2"
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              "name": "\u0027Elixir.HtmlSanitizeEx.Scrubber.HTML5\u0027:sanitize/1"
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            {
              "name": "\u0027Elixir.HtmlSanitizeEx\u0027:html5/1"
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              "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\u003einput\u003c/code\u003e element, and the sanitized output must be rendered to other users.\u003c/p\u003e\n\u003cp\u003eThe rendering page must also contain a form with an \u003ccode\u003eid\u003c/code\u003e, since that \u003ccode\u003eid\u003c/code\u003e is what the injected \u003ccode\u003eform\u003c/code\u003e attribute binds to.\u003c/p\u003e"
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              "value": "Only `HtmlSanitizeEx.html5/1`, and custom scrubbers declared with `use HtmlSanitizeEx, extend: :html5`, allow the `input` element, and the sanitized output must be rendered to other users.\n\nThe rendering page must also contain a form with an `id`, since that `id` is what the injected `form` attribute binds to."
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              "value": "\u003cp\u003eURL Redirection to Untrusted Site (\u0027Open Redirect\u0027) vulnerability in the HTML5 scrubber in rrrene html_sanitize_ex allows an unauthenticated remote attacker to retarget a form already on the rendering page and receive whatever the victim submits, including credentials, via the \u003ccode\u003eform\u003c/code\u003e and \u003ccode\u003eformaction\u003c/code\u003e attributes on an \u003ccode\u003e\u0026lt;input\u0026gt;\u003c/code\u003e element in sanitized HTML. HTML\u0027s \u003ccode\u003eform\u003c/code\u003e attribute associates an input with any form on the page by its \u003ccode\u003eid\u003c/code\u003e even when the input sits outside that form, and \u003ccode\u003eformaction\u003c/code\u003e on a submit control overrides the owning form\u0027s \u003ccode\u003eaction\u003c/code\u003e. Neither attribute receives a scheme check, so an absolute cross-origin URL survives sanitizing.\u003c/p\u003e\n\u003cp\u003eNo script executes. The scrubber allows neither \u003ccode\u003eform\u003c/code\u003e nor \u003ccode\u003ebutton\u003c/code\u003e, so the attacker cannot introduce a form of their own and the rendering page must already contain a form carrying an \u003ccode\u003eid\u003c/code\u003e.\u003c/p\u003e\n\u003cp\u003eThis issue affects html_sanitize_ex: from 0.3.1 before 1.5.3.\u003c/p\u003e"
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              "value": "URL Redirection to Untrusted Site (\u0027Open Redirect\u0027) vulnerability in the HTML5 scrubber in rrrene html_sanitize_ex allows an unauthenticated remote attacker to retarget a form already on the rendering page and receive whatever the victim submits, including credentials, via the `form` and `formaction` attributes on an `\u003cinput\u003e` element in sanitized HTML. HTML\u0027s `form` attribute associates an input with any form on the page by its `id` even when the input sits outside that form, and `formaction` on a submit control overrides the owning form\u0027s `action`. Neither attribute receives a scheme check, so an absolute cross-origin URL survives sanitizing.\n\nNo script executes. The scrubber allows neither `form` nor `button`, so the attacker cannot introduce a form of their own and the rendering page must already contain a form carrying an `id`.\n\nThis issue affects html_sanitize_ex: from 0.3.1 before 1.5.3."
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          "value": "URL Redirection to Untrusted Site (\u0027Open Redirect\u0027) vulnerability in the HTML5 scrubber in rrrene html_sanitize_ex allows an unauthenticated remote attacker to retarget a form already on the rendering page and receive whatever the victim submits, including credentials, via the form and formaction attributes on an \u003cinput\u003e element in sanitized HTML. HTML\u0027s form attribute associates an input with any form on the page by its id even when the input sits outside that form, and formaction on a submit control overrides the owning form\u0027s action. Neither attribute receives a scheme check, so an absolute cross-origin URL survives sanitizing.\n\nNo script executes. The scrubber allows neither form nor button, so the attacker cannot introduce a form of their own and the rendering page must already contain a form carrying an id.\n\nThis issue affects html_sanitize_ex: from 0.3.1 before 1.5.3."
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              "description": "CWE-601 URL Redirection to Untrusted Site (\u0027Open Redirect\u0027)",
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        "shortName": "EEF"
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      "title": "html_sanitize_ex HTML5 scrubber keeps attacker-supplied form-association attributes, allowing form hijacking",
      "workarounds": [
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              "base64": false,
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              "value": "\u003cp\u003eSanitize with \u003ccode\u003ebasic_html/1\u003c/code\u003e, \u003ccode\u003emarkdown_html/1\u003c/code\u003e or \u003ccode\u003estrip_tags/1\u003c/code\u003e, none of which allow \u003ccode\u003einput\u003c/code\u003e, or define a custom scrubber that omits it.\u003c/p\u003e\n\u003cp\u003eOmitting the \u003ccode\u003eid\u003c/code\u003e attribute from the page\u0027s own forms, or giving them values an attacker cannot predict, removes the anchor the injected \u003ccode\u003eform\u003c/code\u003e attribute needs.\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 `input`, or define a custom scrubber that omits it.\n\nOmitting the `id` attribute from the page\u0027s own forms, or giving them values an attacker cannot predict, removes the anchor the injected `form` attribute needs."
            }
          ],
          "value": "Sanitize with basic_html/1, markdown_html/1 or strip_tags/1, none of which allow input, or define a custom scrubber that omits it.\n\nOmitting the id attribute from the page\u0027s own forms, or giving them values an attacker cannot predict, removes the anchor the injected form attribute needs."
        }
      ]
    }
  },
  "cveMetadata": {
    "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
    "assignerShortName": "EEF",
    "cveId": "CVE-2026-66370",
    "datePublished": "2026-08-06T14:49:15.841Z",
    "dateReserved": "2026-08-06T10:15:01.808Z",
    "dateUpdated": "2026-08-06T15:42:09.603Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
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      "cve": "CVE-2026-66370",
      "date": "2026-08-08",
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      "percentile": "0.29294"
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}



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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

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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.