Computing apparatus includes a host processor, which runs a virtual machine monitor (VMM), which supports a plurality of virtual machines and includes a cryptographic security software module. A network interface controller (NIC) links the host processor to a network so as to transmit and receive data packets from and to the virtual machines and includes a cryptographic security hardware logic module, which when invoked by the VMM, applies the cryptographic security protocol to the data packets while maintaining a state context of the protocol with respect to each of the virtual machines. Upon encountering an exception in applying the cryptographic security protocol, the NIC transfers the data packet, together with the state context of the cryptographic security protocol with respect to the given virtual machine, to the cryptographic security software module for processing.