CVE-2026-54659: Pagy Pagy I18n Locale Option Is Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2xmw-f8j8-wfxc",
  "modified" : "2026-07-28T22:25:29Z",
  "published" : "2026-07-28T22:25:29Z",
  "aliases" : [ "CVE-2026-54659" ],
  "summary" : "Pagy I18n locale option is not validated before being used in a file path",
  "details" : "### Summary\n\n`Pagy::I18n.locale=` did not validate its argument before using it as a\npath component to load the matching dictionary file (`<locale>.yml`). An\napplication that assigns untrusted input to the locale — e.g. the common\npattern `Pagy::I18n.locale = params[:locale]` — let that input influence\nwhich file Pagy attempted to load.\n\n### Details\n\nThe setter stored the value as-is, and the loader joined it into a path\nand read it:\n\n```ruby\n# gem/lib/pagy/modules/i18n/i18n.rb\ndef locale=(value)\n  Thread.current[:pagy_locale] = value.to_s\nend\n\n# ...later, when translating:\npath = pathnames.reverse.map { |p| p.join(\"#{locale}.yml\") }.find(&:exist?)\ndictionary = YAML.load_file(path)[locale]\n```\n\nBecause the locale was used verbatim, a value such as an absolute path or\na `../`-style string redirected the lookup outside the locales directory.\nPagy's subsequent structural check (`dictionary['pagy']['p11n']`)\nprevents the file's contents from being returned, so this is **not** a\ndirect file read.\n\nFixed in 43.5.6 by constraining the locale to a BCP 47 shape before use:\n\n```ruby\nLOCALE_PATTERN = /\\A[a-zA-Z]{2,8}(-[a-zA-Z0-9]{1,8})*\\z/\n\ndef locale=(value)\n  Thread.current[:pagy_locale] = value.to_s[LOCALE_PATTERN]\nend\n```\n\nAny non-matching value (including `nil`) resolves to the default locale\nand never reaches the file lookup.\n\n### PoC\n\nIn an application that sets `Pagy::I18n.locale = params[:locale]`, the\nloader appends `.yml` and reads `<locale>.yml`, so the request param\ncontrols the target path. For example, pointing it at the app's\n`config/database.yml`:\n\n1. Send a request with `?locale=../../../config/database` (adjust the\n   number of `../` to reach the app root from the gem's `locales/`\n   directory).\n2. Pagy calls `YAML.load_file` on the resulting `…/config/database.yml`.\n3. The outcome differs by whether that `.yml` exists, is readable, parses\n   as YAML, and has Pagy's expected structure — an existing, readable\n   `config/database.yml` raises a different error than a non-existent\n   path (which silently falls back to the default locale). This yields a\n   file-existence / readability oracle for `.yml` paths, and the targeted\n   file is read into the process during the attempt.\n\n### Impact\n\nInformation disclosure (CWE-22 / CWE-200): a file-existence / readability\noracle for `.yml` paths on the host, plus a server-side read of\nattacker-chosen files into the process. The file contents are not\nreturned in the response.\n\nOnly applications that pass **unsanitized end-user input** into\n`Pagy::I18n.locale=` are affected. Applications that set the locale from\ntrusted values are not affected.\n\n**Patched:** pagy 43.5.6.\n**Workaround (if you cannot upgrade):** validate the locale before\nassigning it, e.g.\n`Pagy::I18n.locale = params[:locale].to_s[/\\A[a-zA-Z]{2,8}(-[a-zA-Z0-9]{1,8})*\\z/]`,\nor restrict it to your known set of locales.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "pagy"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "43.0.0"
      }, {
        "fixed" : "43.5.6"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/ddnexus/pagy/security/advisories/GHSA-2xmw-f8j8-wfxc"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ddnexus/pagy/pull/908"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ddnexus/pagy/commit/efcf09690e9fa7d7abdfb987b785a55f87e287df"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/ddnexus/pagy"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ddnexus/pagy/releases/tag/43.5.6"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-200", "CWE-22" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-28T22:25:29Z",
    "nvd_published_at" : null
  }
}