Grav before 2.0.9 Remote Code Execution via FlexDirectory

Grav versions >= 1.7.0 and before 2.0.9 contain a remote code execution vulnerability. FlexDirectory::dynamicDataField() resolves blueprint data-*@: directives by calling call_user_func_array() on attacker-influenced input, validating only that the target is callable (is_callable()) without restricting dangerous functions such as exec, system, passthru, or shell_exec. Because FlexDirectory registers this handler for every Flex directory, it bypasses the validation added to Blueprint::dynamicData() in 2.0.7 (GHSA-fj2p-qj2f-74v5). Any authenticated user with create or update permission on any Flex-based directory (Flex Users, Flex Pages, Flex Objects, or custom Flex types) can execute arbitrary shell commands on the server.