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.

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.


### Patches

Patches are [available on RubyGems](
for all `1.x` minor versions. The patched versions are:

– [1.9.1](
– [1.8.2](
– [1.7.1](
– [1.6.2](
– [1.5.2](
– [1.4.1](
– [1.3.3](
– [1.2.2](
– [1.1.1](
– [1.0.1](

If you are on `main`, it has been patched since

### Workarounds

Configuring a [Content Security Policy](
that does not allow [`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.


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