Vulnerability-Lookup

CVE-2026-34786 (GCVE-0-2026-34786)

Vulnerability from cvelistv5 – Published: 2026-04-02 16:44 – Updated: 2026-04-03 17:38

Title

Rack: Rack::Static header_rules bypass via URL-encoded paths

Summary

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Static#applicable_rules evaluates several header_rules types against the raw URL-encoded PATH_INFO, while the underlying file-serving path is decoded before the file is served. As a result, a request for a URL-encoded variant of a static path can serve the same file without the headers that header_rules were intended to apply. In deployments that rely on Rack::Static to attach security-relevant response headers to static content, this can allow an attacker to bypass those headers by requesting an encoded form of the path. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

Severity ?

5.3 (Medium)


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

CWE

CWE-180 - Incorrect Behavior Order: Validate Before Canonicalize

Assigner

GitHub_M

References

URL

Tags

https://github.com/rack/rack/security/advisories/…

x_refsource_CONFIRM

Impacted products

	Vendor	Product	Version
	rack	rack	Affected: < 2.2.23 Affected: >= 3.0.0.beta1, < 3.1.21 Affected: >= 3.2.0, < 3.2.6

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-34786

Vulnerability from fkie_nvd - Published: 2026-04-02 17:16 - Updated: 2026-04-03 16:10

Severity ?

5.3 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/rack/rack/security/advisories/GHSA-q4qf-9j86-f5mh

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Static#applicable_rules evaluates several header_rules types against the raw URL-encoded PATH_INFO, while the underlying file-serving path is decoded before the file is served. As a result, a request for a URL-encoded variant of a static path can serve the same file without the headers that header_rules were intended to apply. In deployments that rely on Rack::Static to attach security-relevant response headers to static content, this can allow an attacker to bypass those headers by requesting an encoded form of the path. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6."
    }
  ],
  "id": "CVE-2026-34786",
  "lastModified": "2026-04-03T16:10:23.730",
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          "baseScore": 5.3,
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          "integrityImpact": "LOW",
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}

GHSA-Q4QF-9J86-F5MH

Vulnerability from github – Published: 2026-04-02 18:44 – Updated: 2026-04-02 18:44

Summary

Rack:: Static header_rules bypass via URL-encoded paths

Details

Summary

Rack::Static#applicable_rules evaluates several header_rules types against the raw URL-encoded PATH_INFO, while the underlying file-serving path is decoded before the file is served. As a result, a request for a URL-encoded variant of a static path can serve the same file without the headers that header_rules were intended to apply.

In deployments that rely on Rack::Static to attach security-relevant response headers to static content, this can allow an attacker to bypass those headers by requesting an encoded form of the path.

Details

Rack::Static#applicable_rules matches rule types such as :fonts, Array, and Regexp directly against the incoming PATH_INFO. For example:

when :fonts
  /\.(?:ttf|otf|eot|woff2|woff|svg)\z/.match?(path)
when Array
  /\.(#{rule.join('|')})\z/.match?(path)
when Regexp
  rule.match?(path)

These checks operate on the raw request path. If the request contains encoded characters such as %2E in place of ., the rule may fail to match even though the file path is later decoded and served successfully by the static file server.

For example, both of the following requests may resolve to the same file on disk:

/fonts/test.woff
/fonts/test%2Ewoff

but only the unencoded form may receive the headers configured through header_rules.

This creates a canonicalization mismatch between the path used for header policy decisions and the path ultimately used for file serving.

Impact

Applications that rely on Rack::Static header_rules to apply security-relevant headers to static files may be affected.

In affected deployments, an attacker can request an encoded variant of a static file path and receive the same file without the intended headers. Depending on how header_rules are used, this may bypass protections such as clickjacking defenses, content restrictions, or other response policies applied to static content.

The practical impact depends on the configured rules and the types of files being served. If header_rules are only used for non-security purposes such as caching, the issue may have limited security significance.

Mitigation

Update to a patched version of Rack that applies header_rules to a decoded path consistently with static file resolution.
Do not rely solely on Rack::Static header_rules for security-critical headers where encoded path variants may reach the application.
Prefer setting security headers at the reverse proxy or web server layer so they apply consistently to both encoded and unencoded path forms.
Normalize or reject encoded path variants for static content at the edge, where feasible.

Severity ?

5.3 (Medium)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "RubyGems",
        "name": "rack"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.2.23"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "RubyGems",
        "name": "rack"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0.beta1"
            },
            {
              "fixed": "3.1.21"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "RubyGems",
        "name": "rack"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.2.0"
            },
            {
              "fixed": "3.2.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-34786"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-180"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-02T18:44:49Z",
    "nvd_published_at": "2026-04-02T17:16:25Z",
    "severity": "MODERATE"
  },
  "details": "## Summary\n\n`Rack::Static#applicable_rules` evaluates several `header_rules` types against the raw URL-encoded `PATH_INFO`, while the underlying file-serving path is decoded before the file is served. As a result, a request for a URL-encoded variant of a static path can serve the same file without the headers that `header_rules` were intended to apply.\n\nIn deployments that rely on `Rack::Static` to attach security-relevant response headers to static content, this can allow an attacker to bypass those headers by requesting an encoded form of the path.\n\n## Details\n\n`Rack::Static#applicable_rules` matches rule types such as `:fonts`, `Array`, and `Regexp` directly against the incoming `PATH_INFO`. For example:\n\n```ruby\nwhen :fonts\n  /\\.(?:ttf|otf|eot|woff2|woff|svg)\\z/.match?(path)\nwhen Array\n  /\\.(#{rule.join(\u0027|\u0027)})\\z/.match?(path)\nwhen Regexp\n  rule.match?(path)\n```\n\nThese checks operate on the raw request path. If the request contains encoded characters such as `%2E` in place of `.`, the rule may fail to match even though the file path is later decoded and served successfully by the static file server.\n\nFor example, both of the following requests may resolve to the same file on disk:\n\n```text\n/fonts/test.woff\n/fonts/test%2Ewoff\n```\n\nbut only the unencoded form may receive the headers configured through `header_rules`.\n\nThis creates a canonicalization mismatch between the path used for header policy decisions and the path ultimately used for file serving.\n\n## Impact\n\nApplications that rely on `Rack::Static` `header_rules` to apply security-relevant headers to static files may be affected.\n\nIn affected deployments, an attacker can request an encoded variant of a static file path and receive the same file without the intended headers. Depending on how `header_rules` are used, this may bypass protections such as clickjacking defenses, content restrictions, or other response policies applied to static content.\n\nThe practical impact depends on the configured rules and the types of files being served. If `header_rules` are only used for non-security purposes such as caching, the issue may have limited security significance.\n\n## Mitigation\n\n* Update to a patched version of Rack that applies `header_rules` to a decoded path consistently with static file resolution.\n* Do not rely solely on `Rack::Static` `header_rules` for security-critical headers where encoded path variants may reach the application.\n* Prefer setting security headers at the reverse proxy or web server layer so they apply consistently to both encoded and unencoded path forms.\n* Normalize or reject encoded path variants for static content at the edge, where feasible.",
  "id": "GHSA-q4qf-9j86-f5mh",
  "modified": "2026-04-02T18:44:49Z",
  "published": "2026-04-02T18:44:49Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/rack/rack/security/advisories/GHSA-q4qf-9j86-f5mh"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-34786"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/rack/rack"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Rack:: Static header_rules bypass via URL-encoded paths"
}

Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-34786 (GCVE-0-2026-34786)

FKIE_CVE-2026-34786

GHSA-Q4QF-9J86-F5MH

Summary

Details

Impact

Mitigation

Tags

Sightings

Nomenclature