{"id":"CVE-2026-55792","aliases":["GHSA-287w-mxq6-x2cp"],"url":"https://o3.security/vulnerability/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","published":"2026-07-01T23:20:28.993Z","modified":"2026-10-21T02:58:39.793087827Z","cvss":null,"epss":{"score":0.00397,"percentile":0.33503,"asOf":"2026-09-16"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Packagist","name":"craftcms/cms","fixedVersion":"4.18.0"},{"ecosystem":"Packagist","name":"craftcms/cms","fixedVersion":"5.10.0"}],"fix":{"url":"https://github.com/craftcms/cms/pull/18559","label":"craftcms/cms#18559"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55792.json"},{"type":"ADVISORY","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":"FIX","url":"https://github.com/craftcms/cms/pull/18559"},{"type":"PACKAGE","url":"https://github.com/craftcms/cms"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:58:39.793087827Z"}}