Craft CMS Vulnerable to Authenticated RCE via "craft.app.fs.write()" in Twig Templates

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

9.4 · 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 · score source

EPSS

• CVE-2026-28697: 1.19% estimated exploitation activity in the next 30 days; percentile 67.93 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary An 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. --- Proof of Concept Attack Prerequisites - Authenticated administrator account with allowAdminChanges enabled, or access to the System Messages utility Steps to Reproduce 1. Navigate to Utilities → System Messages (/admin/utilities/system-messages) 2. Edit any email template (e.g., "Test Email") and inject the following in the body (or the Subject): - To exploit it by writing to a file system: - Note: Replace the filesystem handle (e.g., hardDisk) with a valid handle configured in the target installation. - To exploit it by writing to a volume: - Note: Replace the volume handle (e.g., images) with a…

Published by the source

3 Mar 2026, 21:00 UTC

Last modified by the source

4 Mar 2026, 18:39 UTC

Source last checked

26 Oct 2026, 14:38 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-v47q-jxvr-p68x

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# Patch Next advisory brief: CVE-2026-28697

Advisory: Craft CMS Vulnerable to Authenticated RCE via "craft.app.fs.write()" in Twig Templates
IDs: CVE-2026-28697, GHSA-v47q-jxvr-p68x
Record: https://patchnext.com/advisories/cve-2026-28697 (revision 1, source checked 26 Oct 2026, 14:38 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: craftcms/cms 5.9.0-beta.1, 4.17.0-beta.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist craftcms/cms: affected >= 5.0.0-RC1, < 5.9.0-beta.1; >= 4.0.0-RC1, < 4.17.0-beta.1; fixed in 5.9.0-beta.1, 4.17.0-beta.1

## Suggested inspection (read-only)
- Packagist craftcms/cms: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on craftcms/cms.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-v47q-jxvr-p68x (GitHub-reviewed advisory GHSA-v47q-jxvr-p68x lists affected ranges: Packagist craftcms/cms >=5.0.0-RC1 =4.0.0-RC1 <4.17.0-beta.1)

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