{"id":"CVE-2026-73492","aliases":["GHSA-5qhf-9phg-95m2"],"url":"https://o3.security/vulnerability/CVE-2026-73492","summary":"Loofah `allowed_uri?` does not detect `javascript:` URIs split by numeric character references without semicolons","details":"## Summary\n\n`Loofah::HTML5::Scrub.allowed_uri?` does not correctly reject `javascript:` or `vbscript:` URIs when the scheme is split by a numeric character reference that has no trailing semicolon. A browser decodes such references and resolves the URL to an executable `javascript:` scheme, while `allowed_uri?` reports it safe.\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 numeric character references with a trailing `;` (` `, ` `, ` `) but did not cover the forms without semicolons.\n\n## Details\n\n`allowed_uri?` decodes HTML entities with `CGI.unescapeHTML`, which decodes numeric character references only when they carry a trailing `;`. A reference without a semicolon such as `:` (colon) or ` ` (tab) is left literal, so the scheme-detection check finds no scheme, and the method falls through to its scheme-less path and returns `true`.\n\nA browser, however, decodes numeric character references even without a trailing semicolon. An encoded colon such as `:` becomes the `:` scheme separator, so `javascript:alert(1)` resolves to `javascript:alert(1)`. Encoded whitespace such as ` ` (tab) is decoded and then stripped from the URL, rejoining the surrounding text, so `java script:alert(1)` also resolves to `javascript:alert(1)`. In both cases the URL executes while `allowed_uri?` approved it as safe.\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 @MoonFuji.","published":"2026-08-12T21:00:24.679Z","modified":"2026-10-21T17:42:37.874425643Z","cvss":null,"epss":{"score":0.00245,"percentile":0.1592,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"RubyGems","name":"loofah","fixedVersion":"2.25.2"}],"fix":{"url":"https://github.com/flavorjones/loofah/commit/f1be9d893b5a8dd79240441a912d8897e74c38c0","label":"flavorjones/loofah@f1be9d8"},"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-2026-73492.json"},{"type":"ADVISORY","url":"https://github.com/flavorjones/loofah/security/advisories/GHSA-5qhf-9phg-95m2"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-73492"},{"type":"FIX","url":"https://github.com/flavorjones/loofah/commit/f1be9d893b5a8dd79240441a912d8897e74c38c0"},{"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":"2026-10-21T17:42:37.874425643Z"}}