Firmware updates represent a critical vector for innovation and maintenance in embedded systems across automotive, medical devices, aerospace, and industrial automation sectors. The increasing complexity of connected embedded systems has amplified the risks associated with insecure update mechanisms, making them prime targets for cyberattacks including malicious firmware injection, man-in-the-middle attacks, rollback exploits, and side-channel breaches. This article presents comprehensive security frameworks successfully deployed in high-assurance environments, highlighting proven strategies such as cryptographically signed payloads, secure bootloaders, ECU whitelisting, and hardware root of trust mechanisms. Drawing from real-world implementations in over-the-air (OTA) platforms for automotive and industrial control systems, the effectiveness of multi-layered defenses in maintaining system integrity and operational safety is demonstrated. The emergence of blockchain-based update validation and post-quantum cryptographic signatures provides enhanced security measures for long-term resilience. These implementations have not only thwarted known attack vectors but also passed stringent compliance audits, reinforcing the critical importance of secure firmware update architecture in national and global security contexts.