NetCap: Data-Plane Capability-Based Defense Against Token Theft in Network Access

—Tokens play a vital role in enterprise network access control by enabling secure authentication and authorization across various protocols (e.g., JSON Web Tokens, OAuth 2.0). This allows users to access authorized resources using valid access tokens, without the need to repeatedly submit credentials. However, the ambient trust granted to all processes within an authorized host, combined with long token lifetimes, creates an opportunity for malicious processes to hijack tokens and impersonate legitimate users. This threat affects a wide range of protocols and has led to numerous real-world incidents. In this paper, we present N ET C AP , a new defense mechanism designed to prevent attackers from using stolen tokens to access unauthorized resources in enterprise environments. The core idea is to introduce unforgeable, process-level capabilities that are bound to authorized processes. These capabilities are continuously embedded in the processes’ network traffic to target resources for validation and are frequently refreshed. This binding between process identity and capability ensures that even if access tokens are stolen by malicious processes, they cannot be used to pass authentication without valid capabilities. To support the high volume of requests generated by processes in the network, N ET C AP introduces a novel data-plane design based on programmable switches and eBPF. Through multiple optimization techniques, our system supports inline generation and embedding of capabilities, allowing large volumes of traffic to be processed at line rate with little overhead. Our extensive evaluations show that N ET C AP maintains line-rate network performance across a variety of protocols and real-world applications with negligible overhead, while effectively securing these applications against token theft attacks.