Vulnerability Instance

Rails::Html::Sanitizer vulnerable to Cross-site Scripting
Versions of Rails::Html::Sanitizer prior to version 1.4.3 are vulnerable to XSS with certain configurations of Rails::Html::Sanitizer which  allows an attacker to inject content when the application developer has overridden the sanitizer's allowed tags to allow both `select` and `style` elements. Code is only impacted if allowed tags are being overridden. 

This may be done via application configuration: ```ruby# In config/application.rbconfig.action_view.sanitized_allowed_tags = ["select", "style"]```

see https://guides.rubyonrails.org/configuring.html#configuring-action-view

Or it may be done with a `:tags` option to the Action View helper `sanitize`: ```<%= sanitize @comment.body, tags: ["select", "style"] %>``` 

see https://api.rubyonrails.org/classes/ActionView/Helpers/SanitizeHelper.html#method-i-sanitize 

It may also be done with Rails::Html::SafeListSanitizer directly: 
```ruby# class-level optionRails::Html::SafeListSanitizer.allowed_tags = ["select", "style"]```  or with
```ruby# instance-level optionRails::Html::SafeListSanitizer.new.sanitize(@article.body, tags: ["select", "style"])```

All users overriding the allowed tags by any of the above mechanisms to include both "select" and "style" are recommended to upgrade immediately. A workaround for this issue can be applied by removing either `select` or `style` from the overridden allowed tags.