view_component Cross-site Scripting vulnerability

### Impact _What kind of vulnerability is it? Who is impacted?_ This is an XSS vulnerability that has the potential to impact anyone rendering a component directly from a controller with the view_component gem. Note that only components that define a [`#call` method](https://viewcomponent.org/guide/templates.html#call) (i.e. instead of using a sidecar template) are affected. The return value of the `#call` method is not sanitized and can include user-defined content. In addition, the return value of the [`#output_postamble` method](https://viewcomponent.org/api.html#output_postamble--string) is not sanitized, which can also lead to XSS issues. ### Patches _Has the problem been patched? What versions should users upgrade to?_ Versions 3.9.0 has been released and fully mitigates both the `#call` and the `#output_postamble` vulnerabilities. ### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_ Sanitize the return value of `#call`, eg: ```ruby class MyComponent < ApplicationComponent def call html_escape("<div>#{user_input}</div>") end end ``` ### References _Are there any links users can visit to find out more?_ https://github.com/ViewComponent/view_component/pull/1950 ### For more information If you have any questions or comments about this advisory: Open an issue in the [github/view_component](https://github.com/github/view_component) project.

Quoted source text, attributed separately from HOL analysis.