{"id":"EEF-CVE-2026-66370","summary":"html_sanitize_ex HTML5 scrubber keeps attacker-supplied form-association attributes, allowing form hijacking","details":"## Summary\n\nURL 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 `\u003cinput\u003e` 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.\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 1.4.5 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 `input`, or define a custom scrubber that omits it.\n\nOmitting the `id` attribute from the page's own forms, or giving them values an attacker cannot predict, removes the anchor the injected `form` attribute needs.\n\n## Configurations\n\nOnly `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.","aliases":["CVE-2026-66370","GHSA-w3f9-jjhw-wwvq"],"modified":"2026-09-08T16:15:02.378584502Z","published":"2026-08-06T14:49:15.841Z","database_specific":{"cwe_ids":["CWE-601"],"capec_ids":["CAPEC-154"],"cpe_ids":["cpe:2.3:a:rrrene:html_sanitize_ex:*:*:*:*:*:*:*:*"]},"references":[{"type":"ADVISORY","url":"https://github.com/rrrene/html_sanitize_ex/security/advisories/GHSA-w3f9-jjhw-wwvq"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-66370.html"},{"type":"FIX","url":"https://github.com/rrrene/html_sanitize_ex/commit/a1e804ed997e780ea71d14393cf2f701330553a6"},{"type":"FIX","url":"https://github.com/rrrene/html_sanitize_ex/commit/21394e758cb0ffe12fb9953c30fdedc6016c8f9e"},{"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-2026-66370.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/rrrene/html_sanitize_ex","events":[{"introduced":"8976d64ea0b77d26093a94a43ec48a3978e8d028"},{"fixed":"a1e804ed997e780ea71d14393cf2f701330553a6"},{"fixed":"21394e758cb0ffe12fb9953c30fdedc6016c8f9e"}]}],"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-2026-66370.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"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"}],"credits":[{"name":"Peter Ullrich","type":"FINDER"},{"name":"Jonatan Männchen / EEF","type":"ANALYST"},{"name":"René Föhring","type":"REMEDIATION_DEVELOPER"}]}