{"id":"CVE-2026-73491","aliases":["GHSA-8whx-365g-h9vv"],"url":"https://o3.security/vulnerability/CVE-2026-73491","summary":"Loofah `allowed_uri?` does not detect `javascript:` URIs split by named whitespace character references","details":"## Summary\n\n`Loofah::HTML5::Scrub.allowed_uri?` does not correctly reject `javascript:` URIs when the scheme is split or prefixed by the HTML5 named character references `	` (tab) or `
` (line feed).\n\nThis is a bypass of the fix for [GHSA-46fp-8f5p-pf2m](https://github.com/flavorjones/loofah/security/advisories/GHSA-46fp-8f5p-pf2m), which handled the equivalent numeric character references (`	`, `
`, `
`) but did not cover the named forms.\n\n## Details\n\n`allowed_uri?` decodes HTML entities with `CGI.unescapeHTML`, which handles numeric character references but not HTML5 named character references. Payloads like `java	script:alert(1)` are therefore left intact, so the method does not recognize the `javascript:` scheme and returns `true`. A browser, however, decodes `	` and `
` to tab and line feed and strips them from the URL during parsing, producing `javascript:alert(1)`.\n\n`	` and `
` are the only relevant named character references: across the HTML5 named-character table, they are the only two that decode to characters the WHATWG URL parser strips from a URL (U+0009 and U+000A; there is no named reference for U+000D). ` ` / ` ` decode to U+00A0, which browsers do not strip, so they aren't usable for this bypass.\n\nNote that Loofah's default `sanitize()` path is **not** affected, because Nokogiri decodes or entity-escapes HTML entities during parsing before Loofah evaluates the URI protocol. This issue only affects callers of the public `allowed_uri?` string-level helper that pass it HTML-encoded strings.\n\n## Impact\n\nCallers that validate a user-controlled URL with `Loofah::HTML5::Scrub.allowed_uri?` and then render the approved value into an `href` or other browser-interpreted URI attribute may be vulnerable to cross-site scripting (XSS). This includes applications that call `allowed_uri?` directly, as well as higher-level features built on top of it, such as Action Text 8.2's markdown link validation.\n\n## Mitigation\n\nUpgrade to Loofah >= 2.25.2.\n\n## Credit\n\nResponsibly reported by GitHub user @connorshea.","published":"2026-08-12T20:59:18.589Z","modified":"2026-09-11T03:48:36.720334668Z","cvss":null,"epss":{"score":0.00245,"percentile":0.1588,"asOf":"2026-09-16"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"RubyGems","name":"loofah","fixedVersion":"2.25.2"}],"fix":{"url":"https://github.com/flavorjones/loofah/commit/5e91af861e3cdab47b91dd0b81f3afdfd13a5e19","label":"flavorjones/loofah@5e91af8"},"references":[{"type":"WEB","url":"https://github.com/flavorjones/loofah/releases/tag/v2.25.2"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/73xxx/CVE-2026-73491.json"},{"type":"ADVISORY","url":"https://github.com/flavorjones/loofah/security/advisories/GHSA-8whx-365g-h9vv"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-73491"},{"type":"FIX","url":"https://github.com/flavorjones/loofah/commit/5e91af861e3cdab47b91dd0b81f3afdfd13a5e19"},{"type":"FIX","url":"https://github.com/flavorjones/loofah/pull/308"},{"type":"PACKAGE","url":"https://github.com/flavorjones/loofah"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-11T03:48:36.720334668Z"}}