From 4.0.0-X up to and including 9.2.0-X are safe for ninjhax, if X is between 7 and 20.
ARM11 userland homebrew is possible using Cubic Ninja, YouTube, or IronFall from system versions 9.0.0-X up to and including 9.9.0-X, for X up to and including 26.
Full system control exploits are only known for system versions up to and including 9.2.0.