GHSA-whrj-4476-wvmp is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in rack. O3 Security confirms whether GHSA-whrj-4476-wvmp is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Stored XSS in Rack::Directory via javascript: filenames rendered into anchor href
Real-World Exposure
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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 | 2.2.22 |
| 💎RubyGems | rack | ≥ 3.0.0.beta1&&< 3.1.20 | 3.1.20 |
| 💎RubyGems | rack | ≥ 3.2.0&&< 3.2.5 | 3.2.5 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rack. 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 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
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-whrj-4476-wvmp 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-whrj-4476-wvmp. 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-whrj-4476-wvmp in your dependencies?
O3 detects GHSA-whrj-4476-wvmp across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.