The increasing reliance on Field Programmable Gate Arrays (FPGAs) in security-critical applications underscores the need for robust protection mechanisms against cyber threats such as buffer overflow and injection attacks. This paper presents Cybershield, a novel integration of a Trusted Execution Environment (TEE) within RadPC, a radiation-tolerant softcore processor featuring Quad Modular Redundancy (QMR). Leveraging RadPC’s four-core architecture, Cybershield’s TEE employs secure boot from non-volatile memory to initialize RadPC’s cores with obfuscated instruction codes. The opcode obfuscation and a hardware-based anti-voter mechanism prevent the execution of unauthorized code and detect Indicators of Compromise (IoCs). By implementing secure boot and opcode obfuscation, Cybershield mitigates common attack vectors while maintaining software redundancy and recoverability. Experimental validation demonstrates the system’s ability to detect buffer overflow attacks and prevent unauthorized code execution. While the integration of a TEE introduces computational overhead and development constraints due to RadPC’s bare-metal environment, this work lays the foundation for combining hardware and software redundancy to enhance the security of embedded systems.