{"affected":[{"package":{"ecosystem":"Hex","name":"html_sanitize_ex","purl":"pkg:hex/html_sanitize_ex"},"ranges":[{"events":[{"introduced":"0.3.1"},{"fixed":"1.5.3"}],"type":"SEMVER"}],"versions":["0.3.1","1.0.0","1.0.1","1.1.0-rc1","1.1.0","1.1.1","1.2.0","1.3.0-rc1","1.3.0-rc2","1.3.0-rc3","1.3.0","1.4.0","1.4.1","1.4.2","1.4.3","1.4.4-rc.0","1.4.4","1.5.0-rc.0","1.5.0","1.5.1","1.5.2"]},{"ranges":[{"events":[{"introduced":"8976d64ea0b77d26093a94a43ec48a3978e8d028"},{"fixed":"a1e804ed997e780ea71d14393cf2f701330553a6"}],"repo":"https://github.com/rrrene/html_sanitize_ex","type":"GIT"}]}],"aliases":["GHSA-w3f9-jjhw-wwvq","CVE-2026-66370"],"credits":[{"name":"Peter Ullrich","type":"FINDER"},{"name":"Jonatan Männchen / EEF","type":"ANALYST"},{"name":"René Föhring","type":"REMEDIATION_DEVELOPER"}],"database_specific":{"capec_ids":["CAPEC-154"],"cpe_ids":["cpe:2.3:a:rrrene:html_sanitize_ex:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-601"]},"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 <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.\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.\n\n## Workaround\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## Configuration\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.","id":"EEF-CVE-2026-66370","modified":"2026-08-06T14:49:16.432048Z","published":"2026-08-06T14:49:15.841Z","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":"PACKAGE","url":"https://hex.pm/packages/html_sanitize_ex"}],"related":[],"schema_version":"1.7.3","severity":[{"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","type":"CVSS_V4"}],"summary":"html_sanitize_ex HTML5 scrubber keeps attacker-supplied form-association attributes, allowing form hijacking","upstream":[]}