Technologies for untrusted code execution include a computing device having a processor with sandbox support. The computing device executes code included in a native domain in a non-privileged, native processor mode. The computing device may invoke a sandbox jump processor instruction during execution of the code in the native domain to enter a sandbox domain. The computing device executes code in the sandbox domain in a non-privileged, sandbox processor mode in response to invoking the sandbox jump instruction. While executing in the sandbox processor mode, the processor denies access to memory outside of the sandbox domain and may deny execution of one or more prohibited instructions. From the sandbox domain, the computing device may execute a sandbox exit instruction to exit the sandbox domain and resume execution in the native domain. The computing device may execute processor instructions to configure the sandbox domain. Other embodiments are described and claimed.