CVE-2026-73491: Loofah ` URIs Split By Named Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-8whx-365g-h9vv",
  "modified" : "2026-08-12T20:59:24Z",
  "published" : "2026-07-21T15:04:14Z",
  "aliases" : [ "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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "loofah"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.25.0"
      }, {
        "fixed" : "2.25.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/flavorjones/loofah/security/advisories/GHSA-8whx-365g-h9vv"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/flavorjones/loofah/commit/5e91af861e3cdab47b91dd0b81f3afdfd13a5e19"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/flavorjones/loofah"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/flavorjones/loofah/releases/tag/v2.25.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-184" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-21T15:04:14Z",
    "nvd_published_at" : null
  }
}