CVE-2024-28199 (phlex): Cross-site Scripting (XSS) possible with maliciously formed HTML attribute names and values in Phlex

Ruby Security Advisory

There is a potential cross-site scripting (XSS) vulnerability that
can be exploited via maliciously crafted user data. This was due
to improper case-sensitivity in the code that was meant to prevent
these attacks.

### Impact

If you render an `` tag with an `href` attribute set to a
user-provided link, that link could potentially execute JavaScript
when clicked by another user.

“`ruby
a(href: user_profile) { “Profile” }
“`

If you splat user-provided attributes when rendering any HTML or
SVG tag, malicious event attributes could be included in the output,
executing JavaScript when the events are triggered by another user.

“`ruby
h1(**JSON.parse(user_attributes))
“`

### Patches

Patches are [available on RubyGems](https://rubygems.org/gems/phlex)
for all `1.x` minor versions. The patched versions are:

– [1.9.1](https://rubygems.org/gems/phlex/versions/1.9.1)
– [1.8.2](https://rubygems.org/gems/phlex/versions/1.8.2)
– [1.7.1](https://rubygems.org/gems/phlex/versions/1.7.1)
– [1.6.2](https://rubygems.org/gems/phlex/versions/1.6.2)
– [1.5.2](https://rubygems.org/gems/phlex/versions/1.5.2)
– [1.4.1](https://rubygems.org/gems/phlex/versions/1.4.1)
– [1.3.3](https://rubygems.org/gems/phlex/versions/1.3.3)
– [1.2.2](https://rubygems.org/gems/phlex/versions/1.2.2)
– [1.1.1](https://rubygems.org/gems/phlex/versions/1.1.1)
– [1.0.1](https://rubygems.org/gems/phlex/versions/1.0.1)

If you are on `main`, it has been patched since
[`aa50c60`](https://github.com/phlex-ruby/phlex/commit/aa50c604cdee1d0ce7ef068a4c66cbd5d43f96a1)

### Workarounds

Configuring a [Content Security Policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy)
that does not allow [`unsafe-inline`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy#unsafe-inline)
would effectively prevent this vulnerability from being exploited.

### References

In addition to upgrading to a patched version of Phlex, we strongly
recommend configuring a Content Security Policy header that does not
allow `unsafe-inline`. Here’s how you can configure a Content Security
Policy header in Rails.
https://guides.rubyonrails.org/security.html#content-security-policy-header

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