Free netjail software for linux

netjail provides an user-space solution for prohibiting a process from accessing the network.

Netjail is a user-space mechanism for restricting the socket connection attempts that a process makes. This makes it very useful for studying and/or foiling spyware and other software that has covert "home-calling" features.

It is implemented as a shared library which is preloaded when launching the suspect program (via the LD_PRELOAD mechanism available in most moderm Unix systems). This library intercepts socket() and connect() calls to the standard socket library and logs the attempts.

Based on environment variables, detailed rules can be put in place about which addresses will be allowed to connect. Connections that are disallowed will return the ECONNREFUSED (Connection Refused) error, which is most likely to be gracefully handled by hidden spyware functionality.