Craft is a content management system. Versions of Craft CMS on the 4.x branch prior to 4.14.13 and on the 5.x branch prior to 5.6.16 contains a potential remote code execution vulnerability via Twig SSTI. One must have administrator access and `ALLOW_ADMIN_CHANGES` must be enabled for this to work. Users should update to the patched versions 4.14.13 or 5.6.15 to mitigate the issue.
The product uses a template engine to insert or process externally-influenced input, but it does not neutralize or incorrectly neutralizes special elements or syntax that can be interpreted as template expressions or other code directives when processed by the engine.