craftcms/cms security advisory

CVE-2026-28697: Craft CMS Vulnerable to Authenticated RCE via "craft.app.fs.write()" in Twig Templates

CVE-2026-28697 is a critical-severity remote code execution vulnerability in the PHP package craftcms/cms (CVSS 9.1), published 4 March 2026. It is fixed in 4.17.0-beta.1 and 5.9.0-beta.1, one per release line; earlier versions on each line are affected. Exploiting it needs an admin-level account.

critical 9.1 published 2026-03-04 · updated 2026-06-17

Affected versions: >= 4.0.0-RC1, < 4.17.0-beta.1
>= 5.0.0-RC1, < 5.9.0-beta.1
Fixed in: 4.17.0-beta.1, 5.9.0-beta.1
Newest release: 5.12.0
Severity: Critical · CVSS 9.1
Type: Remote code execution
CWE-1336
Exploited in the wild: Not on the CISA KEV list
checked 2026-11-04

Is your craftcms/cms version affected?

Run composer show craftcms/cms in your project, then enter the version. We check it against this and every other known craftcms/cms advisory.

Who can exploit CVE-2026-28697

Access: A high-privilege account in the app, such as an admin.

CVSS vector (scored by NVD): CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

Your app is only exposed if it uses the affected part of craftcms/cms. The advisory below says which part that is. If you are not sure, upgrade anyway: it costs less than finding out.

How to fix CVE-2026-28697 in craftcms/cms

Find the installed version: composer show craftcms/cms. If you never required it yourself, composer why craftcms/cms shows which package pulls it in.
Update it: composer update craftcms/cms --with-all-dependencies. You need the fixed version for your release line (4.17.0-beta.1 and 5.9.0-beta.1).
If Composer will not go that high, your composer.json constraint is holding it back. Widen it (for example "craftcms/cms": "^5.9.0-beta.1" if you can take that version), or upgrade the package that requires it.
Run composer audit. It reads the same advisory data and should no longer list CVE-2026-28697.
Commit composer.lock and deploy it. On the server, run composer install --no-dev from the lock file, not composer update.

If you cannot upgrade yet

General hardening for remote code execution issues while the upgrade waits. None of it replaces the fix.

Never pass user-controlled data to unserialize() or to template rendering, and restrict who can edit templates or settings.
Put a web application firewall in front of the app and watch for new PHP files or admin users.
If your app does not use the affected feature, note that in your audit, but still plan the upgrade.

The CVE-2026-28697 advisory

Craft is a content management system (CMS). Prior to 4.17.0-beta.1 and 5.9.0-beta.1, 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. This vulnerability is fixed in 4.17.0-beta.1 and 5.9.0-beta.1.

Description from the CVE record, published by GitHub (the CVE Numbering Authority), via the NVD entry for CVE-2026-28697. Advisory title: “Craft CMS Vulnerable to Authenticated RCE via "craft.app.fs.write()" in Twig Templates”.

References

GitHub advisory GHSA-v47q-jxvr-p68x github.com
Fix commit 9dc2a4a github.com
Pull request #18216 github.com
Pull request #18219 github.com

Other craftcms/cms advisories

critical Craft CMS: Passkey login accepts replayed WebAuthn assertions 2026-08-07
medium CVE-2026-72779: Craft CMS: Arbitrary file read via SplFileObject in non-sandboxed template contexts 2026-08-06
medium CVE-2026-72782: Craft CMS: Authenticated leak of secret environment variables 2026-08-06
medium CVE-2026-72785: Craft CMS: Authorization bypass: view-only Categories user can modify category structure via structures/move-element 2026-08-06
medium CVE-2026-14794: Craft CMS: Missing authorization check allows non-admin control panel users access to user registration metrics 2026-08-06
low CVE-2026-72783: Craft CMS: Incorrect path validation could potentially lead to path traversal 2026-08-06

Need help patching or upgrading? Laskyr does PHP and Laravel security fixes and upgrades. Tell us what you run and we reply with a plan and a price.

Ask about a fix

Where this data comes from

Affected and fixed versions: the Packagist security advisories API (GitHub Advisory Database and FriendsOfPHP), the same data composer audit uses. Synced 2026-11-03.
Description, score, weakness and references: NIST National Vulnerability Database (NVD), checked 2026-11-04. This product uses data from the NVD API but is not endorsed or certified by the NVD.
Exploited-in-the-wild status: the CISA Known Exploited Vulnerabilities catalog, checked 2026-11-04.
Compiled by Daniel Lasek at Laskyr from the sources above. The summary, “who can exploit it”, “how to fix it” and hardening sections are our plain-English reading of the record and are generated from it. The quoted description is the record's own text. Spot an error? Tell us.