{"id":"CVE-2026-66296","summary":"Reflected XSS in oaskit's default HTML error handler","details":"Improper 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[\u003c/code\u003e\u003c/h2\u003e\u003cscript\u003ealert(document.domain)\u003c/script\u003e]=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.","aliases":["EEF-CVE-2026-66296","GHSA-h7xw-x8wr-xpcc"],"modified":"2026-08-06T03:30:58.627949266Z","published":"2026-08-03T19:04:30.556Z","database_specific":{"cwe_ids":["CWE-79"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/66xxx/CVE-2026-66296.json","unresolved_ranges":[{"extracted_events":[{"introduced":"552de8ca0ff60617bea58bcafa451892d61a161c"},{"fixed":"b70c6b2eaf0b11bdd0bbb21b8a87dbb3d46918a1"}],"source":"AFFECTED_FIELD"}],"cna_assigner":"EEF"},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-66296.html"},{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-66296"},{"type":"WEB","url":"https://repo.hex.pm"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/66xxx/CVE-2026-66296.json"},{"type":"ADVISORY","url":"https://github.com/lud/oaskit/security/advisories/GHSA-h7xw-x8wr-xpcc"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-66296"},{"type":"FIX","url":"https://github.com/lud/oaskit/commit/b70c6b2eaf0b11bdd0bbb21b8a87dbb3d46918a1"},{"type":"PACKAGE","url":"https://github.com/lud/oaskit"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/lud/oaskit","events":[{"introduced":"3ca707778b796488d8054c29d31043bc1e3f66e2"},{"fixed":"37f1b7df9d9fd9d0bc3d69ad4759f3c71b174e3b"},{"fixed":"b70c6b2eaf0b11bdd0bbb21b8a87dbb3d46918a1"}],"database_specific":{"source":["DESCRIPTION","REFERENCES"],"extracted_events":[{"introduced":"0.1.0"},{"fixed":"0.14.1"}]}}],"versions":["v0.14.0","v0.13.2","v0.13.1","v0.13.0","v0.12.0","v0.11.0","v0.10.1","v0.10.0","v0.9.1","v0.9.0","v0.8.0","v0.7.0","v0.6.0","v0.5.1","v0.5.0","v0.4.1","v0.4.0","v0.3.1","v0.3.0","v0.2.0","v0.1.2","v0.1.1","v0.1.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-66296.json"}}],"schema_version":"1.8.0","severity":[{"type":"CVSS_V4","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"}]}