Numerous techniques exist to augment the security functionality of commercial off-the-shelf (COTS) applications and operating systems, making them more suitable for use in mission-critical systems. Although individually useful, as a group these techniques present difficulties to system developers because they are not based on a common framework which might simplify integration and promote portability and reuse. The paper presents techniques for developing Generic Software Wrappers-protected, non-bypassable kernel-resident software extensions for augmenting security without modification of COTS source. We describe the key elements of our work: our high-level Wrapper Definition Language (WDL), and our framework for configuring, activating, and managing wrappers. We also discuss code reuse, automatic management of extensions, a framework for system-building through composition, platform-independence, and our experiences with our Solaris and FreeBSD prototypes.