PT-2026-29915 · Rubygems · Rack

Published

2026-04-02

·

Updated

2026-04-02

CVSS v3.1

7.5

High

VectorAV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Summary

Rack::Static determines whether a request should be served as a static file using a simple string prefix check. When configured with URL prefixes such as "/css", it matches any request path that begins with that string, including unrelated paths such as "/css-config.env" or "/css-backup.sql".
As a result, files under the static root whose names merely share the configured prefix may be served unintentionally, leading to information disclosure.

Details

Rack::Static#route file performs static-route matching using logic equivalent to:
ruby
@urls.any? { |url| path.index(url) == 0 }
This checks only whether the request path starts with the configured prefix string. It does not require a path segment boundary after the prefix.
For example, with:
ruby
use Rack::Static, urls: ["/css", "/js"], root: "public"
the following path is matched as intended:
text
/css/style.css
but these paths are also matched:
text
/css-config.env
/css-backup.sql
/csssecrets.yml
If such files exist under the configured static root, Rack forwards the request to the file server and serves them as static content.
This means a configuration intended to expose only directory trees such as /css/... and /js/... may also expose sibling files whose names begin with those same strings.

Impact

An attacker can request files under the configured static root whose names share a configured URL prefix and obtain their contents.
In affected deployments, this may expose configuration files, secrets, backups, environment files, or other unintended static content located under the same root directory.

Mitigation

  • Update to a patched version of Rack that enforces a path boundary when matching configured static URL prefixes.
  • Match only paths that are either exactly equal to the configured prefix or begin with prefix + "/".
  • Avoid placing sensitive files under the Rack::Static root directory.
  • Prefer static URL mappings that cannot overlap with sensitive filenames.

Exploit

Fix

Information Disclosure

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Weakness Enumeration

CWE-200CWE-187

Related Identifiers

GHSA-H2JQ-G4CQ-5PPQ

Affected Products

Rack