GHSA-9p57-h987-4vgx
HIGHPhlex vulnerable to Cross-site Scripting (XSS) via maliciously formed HTML attribute names and values
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
phlex💎phlexReal-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.
The reason these issues were not detected before is the escapes were working as designed. However, their design didn't take into account just how recklessly permissive browser are when it comes to executing unsafe JavaScript via HTML attributes.
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 minor versions released in the last year.
If you are on main, it has been patched since da8f943
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 | all versions | 1.9.3 |
| 💎RubyGems | phlex | ≥ 1.10.0&&< 1.10.2 | 1.10.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for phlex. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update phlex to 1.9.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-9p57-h987-4vgx is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-9p57-h987-4vgx is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-9p57-h987-4vgx. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-9p57-h987-4vgx in your dependencies?
O3 detects GHSA-9p57-h987-4vgx across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.