GHSA-WHRJ-4476-WVMP

Vulnerability from github – Published: 2026-02-17 18:46 – Updated: 2026-03-10 18:41
VLAI
Summary
Stored XSS in Rack::Directory via javascript: filenames rendered into anchor href
Details

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::Directory prefixes 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)

Severity
5.4 (Medium)
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "RubyGems",
        "name": "rack"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.2.22"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "RubyGems",
        "name": "rack"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0.beta1"
            },
            {
              "fixed": "3.1.20"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "RubyGems",
        "name": "rack"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.2.0"
            },
            {
              "fixed": "3.2.5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-25500"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-02-17T18:46:35Z",
    "nvd_published_at": "2026-02-18T20:18:36Z",
    "severity": "MODERATE"
  },
  "details": "## Summary\n\n`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.\n\nThis results in a client-side XSS condition in directory listings generated by `Rack::Directory`.\n\n## Details\n\n`Rack::Directory` renders directory entries using an HTML row template similar to:\n\n```html\n\u003ca href=\u0027%s\u0027\u003e%s\u003c/a\u003e\n```\n\nThe `%s` placeholder is populated directly with the file\u2019s basename. If the basename begins with `javascript:`, the resulting HTML contains an executable JavaScript URL:\n\n```html\n\u003ca href=\u0027javascript:alert(1)\u0027\u003ejavascript:alert(1)\u003c/a\u003e\n```\n\nBecause 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.\n\n## Impact\n\nIf `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:`.\n\nWhen a user visits the directory listing and clicks the entry, arbitrary JavaScript executes in the application\u0027s origin. Exploitation requires user interaction (clicking the malicious entry).\n\n## Mitigation\n\n* Update to a patched version of Rack in which `Rack::Directory` prefixes generated anchors with a relative path indicator (e.g. `./filename`).\n* Avoid exposing user-controlled directories via `Rack::Directory`.\n* Apply a strict Content Security Policy (CSP) to reduce impact of potential client-side execution issues.\n* Where feasible, restrict or sanitize uploaded filenames to disallow dangerous URI scheme prefixes.\n\nHackerOne profile:\nhttps://hackerone.com/thesmartshadow\n\nGitHub account owner:\nAli Firas (@thesmartshadow)",
  "id": "GHSA-whrj-4476-wvmp",
  "modified": "2026-03-10T18:41:32Z",
  "published": "2026-02-17T18:46:35Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/rack/rack/security/advisories/GHSA-whrj-4476-wvmp"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-25500"
    },
    {
      "type": "WEB",
      "url": "https://github.com/rack/rack/commit/f2f225f297b99fbee3d9f51255d41f601fc40aff"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/rack/rack"
    },
    {
      "type": "WEB",
      "url": "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/rack/CVE-2026-25500.yml"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Stored XSS in Rack::Directory via javascript: filenames rendered into anchor href"
}


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