CVE-2026-25500: Stored XSS in Rack :Directory Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-whrj-4476-wvmp",
  "modified" : "2026-03-10T18:41:32Z",
  "published" : "2026-02-17T18:46:35Z",
  "aliases" : [ "CVE-2026-25500" ],
  "summary" : "Stored XSS in Rack::Directory via javascript: filenames rendered into anchor href",
  "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<a href='%s'>%s</a>\n```\n\nThe `%s` placeholder is populated directly with the file’s basename. If the basename begins with `javascript:`, the resulting HTML contains an executable JavaScript URL:\n\n```html\n<a href='javascript:alert(1)'>javascript:alert(1)</a>\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's 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)",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "rack"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.2.22"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "rack"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.0.0.beta1"
      }, {
        "fixed" : "3.1.20"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "rack"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.2.0"
      }, {
        "fixed" : "3.2.5"
      } ]
    } ]
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-17T18:46:35Z",
    "nvd_published_at" : "2026-02-18T20:18:36Z"
  }
}