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

Severity: critical (CVSS 9.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.1% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-03-04 · updated 2026-06-17
Weakness: CWE-1336

Description

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.

Affected products

craftcms cms: from 4.0.0 (excl.) before 4.17.0; from 5.0.0 (excl.) before 5.9.0; 4.0.0, 4.0.0-rc1, 4.0.0-rc2, 4.0.0-rc3, 5.0.0, 5.0.0-rc1 — fixed in 4.17.0, 5.9.0

How to fix

Upgrade to a fixed version: craftcms cms 4.17.0, 5.9.0. Check the vendor advisory for mitigations.

References

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