strongSwan is an open-source IPsec and IKE software suite used to build VPN connections. It runs on gateways and clients to negotiate identities, keys, and security associations, so it sits on the VPN control plane rather than just moving encrypted packets.
That matters because flaws in handshake logic, certificate handling, state management, or plugins can let an attacker crash the service, disrupt authentication, or trigger other trust-boundary failures before any protected traffic is sent. In practice, defenders watch strongSwan updates closely, verify vendor backports, remove unused protocols or plugins, and monitor for unusual negotiation failures on internet-facing VPN endpoints.