GHSA-7g26-2qgj-chfg: CarrierWave has a denylisted_content_type bypass via Unescaped Regex Metacharacters

Summary CarrierWave's content_type_denylist check fails to escape regex metacharacters in string entries, causing the denylist to silently not match the content types it is intended to block. Note: CarrierWave is aware #content_type_denylist is deprecated for the security reason, but it still used by developers, and the problem here isn't denylist allows any filetype, and thats not a vulnerability in carrierwave, its an implementation problem in developers using CarrierWave, the problem is its denylist entries are interpolated directly into a regex without Regexp.quote or anchoring. The denylist is still useful when developers want to ban specific content types but allow everything else. Details In lib/carrierwave/uploader/content_type_denylist.rb:57, string denylist entries are interpolated directly into a regex without Regexp.quote or anchoring: def denylisted_content_type?(denylist, content_type) Array(denylist).any? { |item| content_type =~ /#{item}/ } end The entry "image/svg+xml" becomes the regex /image\/svg+xml/ where + is a quantifier meaning "one or more g", not a literal +. This regex never matches the real MIME type "image/svg+xml" which contains a literal +. This is inconsistent with the allowlist implementation at lib/carrierwave/uploader/content_type_allowlist.rb:53-57, which correctly applies both Regexp.quote and a \A anchor: rubydef allowlisted_content_type?(allowlist, content_type) Array(allowlist).any? do |item| item = Regexp.quote(item) if item.class != Regexp content_type =~ /\A#{item}/ end end Other affected MIME types include application/xhtml+xml and any type containing regex metacharacters. Fix: Apply Regexp.quote for string entries and anchor with \A, matching the existing allowlist implementation: rubydef denylisted_content_type?(denylist, content_type) Array(denylist).any? do |item| item = Regexp.quote(item) if item.class != Regexp content_type =~ /\A#{item}/ end end PoC app.rb require "sinatra" require "carrierwave" require "fil