Possible XSS vulnerability with certain configurations of rails-html-sanitizer

Summary

There is a possible XSS vulnerability with certain configurations of Rails::Html::Sanitizer. This is due to an incomplete fix of CVE-2022-32209.

• Versions affected: ALL
• Not affected: NONE
• Fixed versions: 1.4.4

Impact

A possible XSS vulnerability with certain configurations of Rails::Html::Sanitizer may allow an attacker to inject content if 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 using either of the following two mechanisms:

1. Using the Rails configuration config.action_view.sanitized_allow_tags=:

# In config/application.rb
config.action_view.sanitized_allowed_tags = ["select", "style"]

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

2. Using the class method Rails::Html::SafeListSanitizer.allowed_tags=:

# class-level option
Rails::Html::SafeListSanitizer.allowed_tags = ["select", "style"]

All users overriding the allowed tags by either of the above mechanisms to include both "select" and "style" should either upgrade or use one of the workarounds immediately.

NOTE: Code is not impacted if allowed tags are overridden using either of the following mechanisms:

• the :tags option to the Action View helper method sanitize.
• the :tags option to the instance method SafeListSanitizer#sanitize.

Workarounds

Remove either "select" or "style" from the overridden allowed tags.

References

• CWE - CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (4.9)
• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-32209
• https://hackerone.com/reports/1654310

Credit

This vulnerability was responsibly reported by Dominic Breuker.