A security association (SA) is the shared set of parameters two systems agree on before they exchange protected traffic. In IPsec, an SA defines the encryption and integrity algorithms, keys, lifetimes, and other rules used to secure one direction of communication over a tunnel.
Security associations matter because they are the trust contract for the connection. If an attacker can interfere with SA negotiation, they may weaken protection, disrupt the tunnel, or exploit flaws in the code that builds it. That is why IKE and IPsec components are high-value targets: they sit at the network edge and handle authentication and tunnel setup before application traffic flows. Defenders should monitor which hosts negotiate SAs, restrict unnecessary exposure, and patch any bug in the negotiation path quickly, especially on VPN or remote-access systems.