GHSA-whrj-4476-wvmp is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in rack. A fix is available for rack — see the affected versions and patch details below.
Stored XSS in Rack::Directory via javascript: filenames rendered into anchor href
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-whrj-4476-wvmp.
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-whrj-4476-wvmp 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
rack💎rack💎rackReal-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
Summary
Rack::Directory generates an HTML directory index where each file entry is rendered as a clickable link. If a file exists on disk whose basename begins with the javascript: scheme (e.g. javascript:alert(1)), the generated index includes an anchor whose href attribute is exactly javascript:alert(1). Clicking this entry executes arbitrary JavaScript in the context of the hosting application.
This results in a client-side XSS condition in directory listings generated by Rack::Directory.
Details
Rack::Directory renders directory entries using an HTML row template similar to:
<a href='%s'>%s</a>
The %s placeholder is populated directly with the file’s basename. If the basename begins with javascript:, the resulting HTML contains an executable JavaScript URL:
<a href='javascript:alert(1)'>javascript:alert(1)</a>
Because the value is inserted directly into the href attribute without scheme validation or normalization, browsers interpret it as a JavaScript URI. When a user clicks the link, the JavaScript executes in the origin of the Rack application.
Impact
If Rack::Directory is used to expose filesystem contents over HTTP, an attacker who can create or upload files within that directory may introduce a malicious filename beginning with javascript:.
When a user visits the directory listing and clicks the entry, arbitrary JavaScript executes in the application's origin. Exploitation requires user interaction (clicking the malicious entry).
Mitigation
- Update to a patched version of Rack in which
Rack::Directoryprefixes generated anchors with a relative path indicator (e.g../filename). - Avoid exposing user-controlled directories via
Rack::Directory. - Apply a strict Content Security Policy (CSP) to reduce impact of potential client-side execution issues.
- Where feasible, restrict or sanitize uploaded filenames to disallow dangerous URI scheme prefixes.
HackerOne profile: https://hackerone.com/thesmartshadow
GitHub account owner: Ali Firas (@thesmartshadow)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | rack | all versions | 2.2.22bundle update rack --conservative |
| 💎RubyGems | rack | ≥ 3.0.0.beta1&&< 3.1.20 | 3.1.20bundle update rack --conservative |
| 💎RubyGems | rack | ≥ 3.2.0&&< 3.2.5 | 3.2.5bundle update rack --conservative |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update rack to 2.2.22 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-whrj-4476-wvmp 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.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-whrj-4476-wvmp can be triaged on real exposure rather than presence alone.
Tailored to GHSA-whrj-4476-wvmp. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.Source: Red Hat security advisory for GHSA-whrj-4476-wvmp (CC BY 4.0)
Frequently Asked Questions
Is GHSA-whrj-4476-wvmp in your dependencies?
O3 Security finds GHSA-whrj-4476-wvmp across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.