{"id":"GHSA-5qhf-9phg-95m2","title":"Loofah `allowed_uri?` does not detect `javascript:` URIs split by numeric character references without semicolons","summary":"Loofah `allowed_uri?` does not detect `javascript:` URIs split by numeric character references without semicolons","severity":"low","cwe":["CWE-79","CWE-184"],"vendor":"loofah","product":"loofah","ecosystem":"rubygems","affected":["loofah >= 2.25.0, < 2.25.2"],"patched":["loofah 2.25.2"],"published":"2026-07-21","updated":"2026-07-21","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-5qhf-9phg-95m2","references":[{"url":"https://github.com/flavorjones/loofah/security/advisories/GHSA-5qhf-9phg-95m2"},{"url":"https://github.com/flavorjones/loofah/commit/f1be9d893b5a8dd79240441a912d8897e74c38c0"},{"url":"https://github.com/flavorjones/loofah/releases/tag/v2.25.2"},{"url":"https://github.com/advisories/GHSA-5qhf-9phg-95m2"}],"tags":["ghsa","rubygems"],"ingestedAt":"2026-07-21T22:55:08.677Z","slug":"GHSA-5qhf-9phg-95m2","body":"## Overview\n\n## 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 `;` (`&#9;`, `&#10;`, `&#13;`) 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 `&#58` (colon) or `&#9` (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 `&#58` becomes the `:` scheme separator, so `javascript&#58alert(1)` resolves to `javascript:alert(1)`. Encoded whitespace such as `&#9` (tab) is decoded and then stripped from the URL, rejoining the surrounding text, so `java&#9script: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.\n\n## Affected packages\n\n- `loofah >= 2.25.0, < 2.25.2`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `loofah 2.25.2`","depth":"sunlit","depthScore":14,"depthScoreParts":{"impact":13.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}