Cross-site Scripting (XSS) possible with maliciously formed HTML attribute names and values in Phlex

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 <a> 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.

h1(**JSON.parse(user_attributes))

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 aa50c60

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. https://guides.rubyonrails.org/security.html#content-security-policy-header