SELinux (Security-Enhanced Linux) was developed by the U.S National Security Agency and essentially enforces security policies that limits what a user or program can do by implementing MAC (Mandatory Access Control) in the Linux kernel. It defines a security policy that controls many different things such as files, devices, sockets, ports and even some processes. The Security-enhanced Linux's features are designed to enforce the separation of information based on confidentiality and integrity requirements. They are designed for preventing processes from reading data and programs, tampering with data and programs, bypassing application security mechanisms, executing untrustworthy programs, or interfering with other processes in violation of the system security policy. They also help to confine the potential damage that can be caused by malicious or flawed programs. They should also be useful for enabling a single system to be used by users with differing security authorizations to access multiple kinds of information with differing security requirements without compromising those security requirements.

SELinux can be in one of three states or modes and the first mode would be the enforcing/active state. This is the default state wherein no user or program will be able to do anything not permitted by the security policy. The next mode would be the permissive/warn state wherein SELinux sends warning message to a log but does not enforce the security policy. Later, an administrator could use the log to build a security policy that matches the requirements given. The last mode would be the disabled state and with this mode, SELinux does not enforce a security policy nor does it issue warnings because no policy is loaded.

The next Linux security technology I want to talk about is iptables and how that security feature works. Iptables is used to