Rack::Static prefix matching can expose unintended files under the static root

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS

• CVE-2026-34785: 0.39% estimated exploitation activity in the next 30 days; percentile 33.68 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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#routefile performs static-route matching using logic equivalent to: 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: the following path is matched as intended: but these paths are also matched: 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…

Published by the source

2 Apr 2026, 18:44 UTC

Last modified by the source

13 May 2026, 15:20 UTC

Source last checked

26 Oct 2026, 15:51 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-h2jq-g4cq-5ppq

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# Patch Next advisory brief: CVE-2026-34785

Advisory: Rack::Static prefix matching can expose unintended files under the static root
IDs: CVE-2026-34785, GHSA-h2jq-g4cq-5ppq
Record: https://patchnext.com/advisories/cve-2026-34785 (revision 1, source checked 26 Oct 2026, 15:51 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: rack 3.2.6, 3.1.21, 2.2.23. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems rack: affected < 2.2.23; >= 3.0.0.beta1, < 3.1.21; >= 3.2.0, < 3.2.6; fixed in 3.1.21, 2.2.23, 3.2.6

## Suggested inspection (read-only)
- RubyGems rack: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on rack.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-h2jq-g4cq-5ppq (GitHub-reviewed advisory GHSA-h2jq-g4cq-5ppq lists affected ranges: RubyGems rack >=0 =3.0.0.beta1 =3.2.0 <3.2.6)

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