SubDomain: Parsimonious Server Security

Internet security incidents have shown that while network cryptography tools like SSL are valuable to Internet service, the hard problem is to protect the server itself from attack. The host security problem is important because attackers know to attack the weakest link, which is vulnerable servers. The problem is hard because securing a server requires securing every piece of software on the server that the attacker can access, which can be a very large set of software for a sophisticated server. Sophisticated security architectures that protect against this class of problem exist, but because they are either complex, expensive, or incompatible with existing application software, most Internet server operators have not chosen to use them.

This paper presents SubDomain: an OS extension designed to provide sufficient security to prevent vulnerability rot in Internet server platforms, and yet simple enough to minimize the performance, administrative, and implementation costs. SubDomain does this by providing a least privilege mechanism for programs rather than for users. By orienting itself to programs rather than users, SubDomain simplifies the security administrator's task of securing the server.

This paper describes the problem space of securing Internet servers, and presents the SubDomain solution to this problem. We describe the design, implementation, and operation of SubDomain, and provide working examples and performance metrics for services such as HTTP, SMTP, POP, and DNS protected with SubDomain.