Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. From 2.25.0 until 2.25.2, Loofah::HTML5::Scrub.allowed_uri? does not reject javascript: or vbscript: URIs whose scheme is split by semicolon-less numeric character references such as &#58, &#9, &#10, or &#13. CGI.unescapeHTML leaves these references encoded, so allowed_uri? reports the URL safe even though a browser decodes an encoded colon or strips encoded whitespace and executes the resulting URI scheme. This issue affects only callers that pass HTML-encoded strings directly to allowed_uri?; Loofah's default sanitize() path is not affected. This issue is fixed in version 2.25.2.

Affected: RubyGems: loofah

## Summary

`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.

This 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.

## Details

`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`.

A 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.

Note that Loofah's default `sanitize()` path is **not**…

Affected: Ubuntu:16.04:LTS: ruby-loofah, Ubuntu:18.04:LTS: ruby-loofah, Ubuntu:20.04:LTS: ruby-loofah, Ubuntu:22.04:LTS: ruby-loofah, Ubuntu:24.04:LTS: ruby-loofah, Ubuntu:26.04:LTS: ruby-loofah

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. From 2.25.0 until 2.25.2, Loofah::HTML5::Scrub.allowed_uri? does not reject javascript: or vbscript: URIs whose scheme is split by semicolon-less numeric character references such as &#58, &#9, &#10, or &#13. CGI.unescapeHTML leaves these references encoded, so allowed_uri? reports the URL safe even though a browser decodes an encoded colon or strips encoded whitespace and executes the resulting URI scheme. This issue affects only callers that pass HTML-encoded strings directly to allowed_uri?; Loofah's default sanitize() path is not affected. This issue is fixed in version 2.25.2.