PHP's two common template engines both lead to code execution from a template injection, though by different routes. Twig (the default in Symfony and widely used standalone) is reached through its filter and function callbacks; Smarty exposes PHP more directly through dedicated constructs that have tightened over versions.

Detect Twig with {{7*7}} returning 49, and Smarty with {$smarty.version} echoing the version string (Smarty uses single braces, so {7*7} is not a reliable probe and may error).

Engines#

• Twig: filter/map callbacks to system, and the historical _self registerUndefinedFilterCallback.
• Smarty: the {php} tag and static-method constructs, with their version gating.

References#

• Twig and Smarty documentation (sandbox, security policy)
• PortSwigger Web Security Academy: Server-side template injection