{"affected":[{"package":{"ecosystem":"Hex","name":"oaskit","purl":"pkg:hex/oaskit"},"ranges":[{"events":[{"introduced":"0.1.0"},{"fixed":"0.14.1"}],"type":"SEMVER"}],"versions":["0.1.0","0.1.1","0.1.2","0.2.0","0.3.0","0.3.1","0.4.0","0.4.1","0.5.0","0.5.1","0.6.0","0.7.0","0.8.0","0.9.0","0.9.1","0.10.0","0.10.1","0.11.0","0.12.0","0.13.0","0.13.1","0.13.2","0.14.0"]},{"ranges":[{"events":[{"introduced":"552de8ca0ff60617bea58bcafa451892d61a161c"},{"fixed":"b70c6b2eaf0b11bdd0bbb21b8a87dbb3d46918a1"}],"repo":"https://github.com/lud/oaskit","type":"GIT"}]}],"aliases":["GHSA-h7xw-x8wr-xpcc","CVE-2026-66296"],"credits":[{"name":"Ludovic Dem","type":"FINDER"},{"name":"Ludovic Dem","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"ANALYST"}],"database_specific":{"capec_ids":["CAPEC-591"],"cpe_ids":["cpe:2.3:a:lud:oaskit:*:*:*:*:*:elixir:*:*"],"cwe_ids":["CWE-79"]},"details":"## Summary\n\nImproper Neutralization of Input During Web Page Generation (XSS) vulnerability in lud oaskit allows reflected cross-site scripting via the default HTML error handler.\n\nOaskit.ErrorHandler.Default.format\\_reason/4 and Oaskit.ErrorHandler.Default.reason\\_to\\_html/1 in lib/oaskit/error\\_handler/default.ex render request-validation failures as an HTML page whenever the request's Accept header contains html, interpolating request-controlled strings into that page without HTML escaping. The unescaped values are object keys taken from a request body or from an object or deepObject query parameter, which appear in the JSON Schema error's instance path when a schema rejects them (for example under additionalProperties: false), and the raw Content-Type header, reflected in unsupported-media-type errors when it fails to parse.\n\nBecause browsers send Accept: text/html on ordinary top-level navigation, a crafted GET link is sufficient to trigger the error page; no form submission, custom Content-Type, or attacker-controlled script on the victim's side is required. A payload such as filter\\[</code></h2><script>alert(document.domain)</script>\\]=x terminates the enclosing markup and the injected script executes in the origin of the application using oaskit, giving it access to that origin's cookies, session, and same-origin responses.\n\nBoth HTML error rendering and the vulnerable handler are enabled by default: Oaskit.Plugs.ValidateRequest defaults :html\\_errors to true and :error\\_handler to Oaskit.ErrorHandler.Default, so applications following the documented usage are affected without any opt-in.\n\nThis issue affects oaskit: from 0.1.0 before 0.14.1.\n\n## Workaround\n\nDisable HTML error rendering so that validation failures are returned as JSON only:\n\nplug Oaskit.Plugs.ValidateRequest, html\\_errors: false\n\nThis prevents the vulnerable HTML page from being rendered at all, on any oaskit version. Alternatively, configure a custom :error\\_handler that does not emit HTML built from request-derived values.","id":"EEF-CVE-2026-66296","modified":"2026-08-03T19:04:31.150711Z","published":"2026-08-03T19:04:30.556Z","references":[{"type":"ADVISORY","url":"https://github.com/lud/oaskit/security/advisories/GHSA-h7xw-x8wr-xpcc"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-66296.html"},{"type":"FIX","url":"https://github.com/lud/oaskit/commit/b70c6b2eaf0b11bdd0bbb21b8a87dbb3d46918a1"},{"type":"PACKAGE","url":"https://hex.pm/packages/oaskit"}],"related":[],"schema_version":"1.7.3","severity":[{"score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N","type":"CVSS_V4"}],"summary":"Reflected XSS in oaskit's default HTML error handler","upstream":[]}