{"id":"GHSA-h2jq-g4cq-5ppq","summary":"Rack::Static prefix matching can expose unintended files under the static root","details":"## Summary\n\n`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\"`.\n\nAs a result, files under the static root whose names merely share the configured prefix may be served unintentionally, leading to information disclosure.\n\n## Details\n\n`Rack::Static#route_file` performs static-route matching using logic equivalent to:\n\n```ruby\n@urls.any? { |url| path.index(url) == 0 }\n```\n\nThis checks only whether the request path starts with the configured prefix string. It does not require a path segment boundary after the prefix.\n\nFor example, with:\n\n```ruby\nuse Rack::Static, urls: [\"/css\", \"/js\"], root: \"public\"\n```\n\nthe following path is matched as intended:\n\n```text\n/css/style.css\n```\n\nbut these paths are also matched:\n\n```text\n/css-config.env\n/css-backup.sql\n/csssecrets.yml\n```\n\nIf such files exist under the configured static root, Rack forwards the request to the file server and serves them as static content.\n\nThis 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.\n\n## Impact\n\nAn attacker can request files under the configured static root whose names share a configured URL prefix and obtain their contents.\n\nIn affected deployments, this may expose configuration files, secrets, backups, environment files, or other unintended static content located under the same root directory.\n\n## Mitigation\n\n* Update to a patched version of Rack that enforces a path boundary when matching configured static URL prefixes.\n* Match only paths that are either exactly equal to the configured prefix or begin with `prefix + \"/\"`.\n* Avoid placing sensitive files under the `Rack::Static` root directory.\n* Prefer static URL mappings that cannot overlap with sensitive filenames.","aliases":["CVE-2026-34785"],"modified":"2026-07-17T21:14:42.780529374Z","published":"2026-04-02T18:44:25Z","database_specific":{"nvd_published_at":"2026-04-02T17:16:24Z","cwe_ids":["CWE-187","CWE-200"],"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-04-02T18:44:25Z"},"references":[{"type":"WEB","url":"https://github.com/rack/rack/security/advisories/GHSA-h2jq-g4cq-5ppq"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-34785"},{"type":"PACKAGE","url":"https://github.com/rack/rack"},{"type":"WEB","url":"https://github.com/rubysec/ruby-advisory-db/blob/master/gems/rack/CVE-2026-34785.yml"}],"affected":[{"package":{"name":"rack","ecosystem":"RubyGems","purl":"pkg:gem/rack"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.2.23"}]}],"versions":["0.1.0","0.2.0","0.3.0","0.4.0","0.9.0","0.9.1","1.0.0","1.0.1","1.1.0","1.1.1","1.1.1.pre","1.1.2","1.1.3","1.1.4","1.1.5","1.1.6","1.2.0","1.2.1","1.2.2","1.2.3","1.2.4","1.2.5","1.2.6","1.2.7","1.2.8","1.3.0","1.3.0.beta","1.3.0.beta2","1.3.1","1.3.10","1.3.2","1.3.3","1.3.4","1.3.5","1.3.6","1.3.7","1.3.8","1.3.9","1.4.0","1.4.1","1.4.2","1.4.3","1.4.4","1.4.5","1.4.6","1.4.7","1.5.0","1.5.0.beta.1","1.5.0.beta.2","1.5.1","1.5.2","1.5.3","1.5.4","1.5.5","1.6.0","1.6.0.beta","1.6.0.beta2","1.6.1","1.6.10","1.6.11","1.6.12","1.6.13","1.6.2","1.6.3","1.6.4","1.6.5","1.6.6","1.6.7","1.6.8","1.6.9","2.0.0.alpha","2.0.0.rc1","2.0.1","2.0.2","2.0.3","2.0.4","2.0.5","2.0.6","2.0.7","2.0.8","2.0.9","2.0.9.1","2.0.9.2","2.0.9.3","2.0.9.4","2.1.0","2.1.1","2.1.2","2.1.3","2.1.4","2.1.4.1","2.1.4.2","2.1.4.3","2.1.4.4","2.2.0","2.2.1","2.2.10","2.2.11","2.2.12","2.2.13","2.2.14","2.2.15","2.2.16","2.2.17","2.2.18","2.2.19","2.2.2","2.2.20","2.2.21","2.2.22","2.2.3","2.2.3.1","2.2.4","2.2.5","2.2.6","2.2.6.1","2.2.6.2","2.2.6.3","2.2.6.4","2.2.7","2.2.8","2.2.8.1","2.2.9"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/04/GHSA-h2jq-g4cq-5ppq/GHSA-h2jq-g4cq-5ppq.json"}},{"package":{"name":"rack","ecosystem":"RubyGems","purl":"pkg:gem/rack"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"3.0.0.beta1"},{"fixed":"3.1.21"}]}],"versions":["3.0.0","3.0.0.beta1","3.0.0.rc1","3.0.1","3.0.10","3.0.11","3.0.12","3.0.13","3.0.14","3.0.15","3.0.16","3.0.17","3.0.18","3.0.2","3.0.3","3.0.4","3.0.4.1","3.0.4.2","3.0.5","3.0.6","3.0.6.1","3.0.7","3.0.8","3.0.9","3.0.9.1","3.1.0","3.1.1","3.1.10","3.1.11","3.1.12","3.1.13","3.1.14","3.1.15","3.1.16","3.1.17","3.1.18","3.1.19","3.1.2","3.1.20","3.1.3","3.1.4","3.1.5","3.1.6","3.1.7","3.1.8","3.1.9"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/04/GHSA-h2jq-g4cq-5ppq/GHSA-h2jq-g4cq-5ppq.json"}},{"package":{"name":"rack","ecosystem":"RubyGems","purl":"pkg:gem/rack"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"3.2.0"},{"fixed":"3.2.6"}]}],"versions":["3.2.0","3.2.1","3.2.2","3.2.3","3.2.4","3.2.5"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/04/GHSA-h2jq-g4cq-5ppq/GHSA-h2jq-g4cq-5ppq.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"}]}