Executive brief
Craft CMS is a content management system used to build and manage websites. A security vulnerability allows authorized users with entry-editing permissions to execute malicious code on the server by manipulating web request headers. This could lead to a full system takeover, unauthorized data access, or disruption of website operations.
Technical details
A Server-Side Template Injection (SSTI) vulnerability exists in Craft CMS versions 5.9.x prior to 5.10.0. The application uses the `renderObjectTemplate()` function to process strings for signed redirect URLs derived from the 'Referer' HTTP header. Because this function does not enforce sandboxing, an authenticated attacker with 'edit entry' permissions can inject malicious Twig templates into the Referer header. When the entry is saved, the template is executed on the server, leading to Remote Code Execution (RCE). The fix involves migrating to `renderSandboxedObjectTemplate()` and explicitly setting return URLs.
Affected products
- Craft CMS CMS >= 5.9.0, < 5.10.0
Timeline
- 2026-04-17: patched: Pull request merged into version 5.10
- 2026-07-01: disclosed: NVD publication date
- 2026-07-06: advisory: GitHub Advisory published