CVE-2026-126079: Action View: Possible XSS vulnerability in Action View text helpers

Action View is a framework for handling view template lookup and rendering and provides view helpers for building HTML. Prior to 8.1.4.1 and 8.0.5.2, with the HTML5 sanitizer (Rails::HTML5::Sanitizer, the default vendor on CRuby for applications using loaddefaults 7.1 or later), Nokogiri before 1.19.5 serializes < and > unescaped inside attribute values. The Action View text helpers highlight and simpleformat sanitize their input and then process the resulting HTML as a string: highlight splits it on tag boundaries to insert matches, and simpleformat splits it into paragraphs on blank lines. An unescaped > or a blank line inside an attribute value could cause markup in that value, which the sanitizer left inert, to be emitted as live elements in the helper's htmlsafe output, possibly leading to XSS. Applications that use the HTML5 sanitizer and pass untrusted text to highlight, or to simpleformat with htmloptions, are affected. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.