CVE-2026-55792: Craft CMS Sensitive File Disclosure / Server-Side Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-287w-mxq6-x2cp",
  "modified" : "2026-07-06T21:29:49Z",
  "published" : "2026-07-06T21:29:49Z",
  "aliases" : [ "CVE-2026-55792" ],
  "summary" : "Craft CMS: Sensitive File Disclosure / Server-Side File Read",
  "details" : "The `dataUrl()` Twig function is included in Craft’s Twig sandbox allowlist, allowing any control panel user granted the `utility:system-messages` permission to embed a file-reading payload into system email templates. When those emails are sent, the server reads the target file and returns its contents as a base64-encoded data URL embedded in the email body. The .env file, which typically contains the database password, CRAFT_SECURITY_KEY, and third-party API keys, passes all of Craft’s existing `dataUrl()` protection checks and is fully exfiltrated. Obtaining CRAFT_SECURITY_KEY enables an attacker to forge session tokens and escalate to full admin account takeover.\n\n## Details\nAffected versions: Craft CMS 4.x, 5.x (confirmed against 5.9.19)\n\nThe vulnerability arises from the combination of three code facts:\n1. dataUrl is in the Twig sandbox allowlist\nsrc/config/twig-sandbox.php, line 115:\nphp'allowedFunctions' => [\n    ...\n    'dataUrl',   // ← allows file reading inside sandboxed templates\n    ...\n],\n\n2. Html::dataUrl() does not block dotfiles\nsrc/helpers/Html.php, lines 1065–1090. The function applies four checks before reading a file:\n\nMust be within the project root .env is at the root\nMust not be in a system directory (config/, vendor/, storage/, templates/) .env is not\nMust not be a .php file  .env has no extension\nFile must exist .env always exists in a Craft install\n\nThere is no check for dotfiles or specifically for .env. All four checks pass silently and file_get_contents() is called, with the result returned as data:text/plain;base64,....\n\n3. System message body is rendered via renderSandboxedString()\nsrc/mail/Mailer.php, lines 181–183:\nphp$subject = $view->renderSandboxedString($systemMessage->subject, $variables);\n$textBody = $view->renderSandboxedString($systemMessage->body, $variables);\n$htmlBody = $view->renderSandboxedString($systemMessage->body, $variables, escapeHtml: true);\n\nAny body content saved to a system message is executed inside the Twig sandbox when the email renders. Because dataUrl is in allowedFunctions, the sandbox policy permits its execution without restriction.\n\nAccess control: The utility:system-messages permission is a non-admin CP permission grantable to any user group via Settings > Users > Groups. It is not restricted to admins.\n\n## Impact\nVulnerability type: Sensitive File Disclosure / Server-Side File Read\nWho is impacted: Any Craft CMS 4.x or 5.x installation where at least one non-admin control panel user has been granted the utility:system-messages permission, and email sending is configured.\n\nResources:\n\n- https://github.com/craftcms/cms/pull/18559",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "craftcms/cms"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.0.0-RC1"
      }, {
        "fixed" : "4.18.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "craftcms/cms"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "5.0.0-RC1"
      }, {
        "fixed" : "5.10.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/craftcms/cms/security/advisories/GHSA-287w-mxq6-x2cp"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-55792"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/craftcms/cms/pull/18559"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/craftcms/cms"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-200" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-06T21:29:49Z",
    "nvd_published_at" : "2026-07-02T00:16:44Z"
  }
}