GHSA-9p57-h987-4vgx 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.
Phlex vulnerable to Cross-site Scripting (XSS) via maliciously formed HTML attribute names and values
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 GHSA-9p57-h987-4vgx.
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.
How urgent is this, really
GHSA-9p57-h987-4vgx plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 379,145 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
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 | 1.9.3bundle update phlex --conservative |
| 💎RubyGems | phlex | ≥ 1.10.0&&< 1.10.2 | 1.10.2bundle update phlex --conservative |
Detection & 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 1.9.3 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-9p57-h987-4vgx can be triaged on real exposure rather than presence alone.
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 Security finds GHSA-9p57-h987-4vgx across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.