CVE-2024-28199 is a high-severity (CVSS 7.1) Cross-site Scripting (XSS) vulnerability in phlex. A fix is available for phlex — see the affected versions and patch details below.
Cross-site Scripting (XSS) possible with maliciously formed HTML attribute names and values in Phlex
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2024-28199.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
phlex💎phlex💎phlex💎phlex💎phlex💎phlex💎phlex💎phlex+2 moreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
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:
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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | phlex | ≥ 1.9.0&&< 1.9.1 | 1.9.1bundle update phlex --conservative |
| 💎RubyGems | phlex | ≥ 1.8.0&&< 1.8.2 | 1.8.2bundle update phlex --conservative |
| 💎RubyGems | phlex | ≥ 1.7.0&&< 1.7.1 | 1.7.1bundle update phlex --conservative |
| 💎RubyGems | phlex | ≥ 1.6.0&&< 1.6.2 | 1.6.2bundle update phlex --conservative |
| 💎RubyGems | phlex | ≥ 1.5.0&&< 1.5.2 | 1.5.2bundle update phlex --conservative |
| 💎RubyGems | phlex | ≥ 1.4.0&&< 1.4.1 | 1.4.1bundle update phlex --conservative |
Affected Products
phlexphlexDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for phlex, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update phlex to 1.9.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2024-28199 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2024-28199 in your dependencies?
Find it across RubyGems, including transitive dependencies.