In actionpack gem >= 6.0.0, a possible XSS vulnerability exists when an application is running in development mode allowing an attacker to send or embed (in another page) a specially crafted URL which can allow the attacker to execute JavaScript in the context of the local application. This vulnerability is in the Actionable Exceptions middleware.

Workarounds

Until such time as the patch can be applied, application developers should disable the Actionable Exceptions middleware in their development environment via a line such as this one in their config/environment/development.rb: config.middleware.delete ActionDispatch::ActionableExceptions

References

• https://nvd.nist.gov/vuln/detail/CVE-2020-8264
• https://hackerone.com/reports/904059
• https://groups.google.com/g/rubyonrails-security/c/yQzUVfv42jk/m/oJWw-xhNAQAJ
• https://github.com/rubysec/ruby-advisory-db/blob/master/gems/actionpack/CVE-2020-8264.yml
• https://groups.google.com/g/rubyonrails-security/c/yQzUVfv42jk