Network applications with high dependability requirements must be carefully tested under communication faults to enhance confidence in proper behavior. Fault injection is very useful for these tests. When the applications use more than one protocol, such as UDP, TCP and RMI, a suitable tool that properly handles all of them is required. However, existing tools either are unable to test this kind of application or impose relevant drawbacks. This paper presents Comform, a communication fault injector for multi-protocol Java applications. It intercepts protocol messages at JVM level and uses firewall rules for fault emulation. The approach is useful for both white and black box testing and preserves the target's source code.