The Agent-to-Agent Handoff Problem: Session Trust and Privilege Escalation Across Agent Boundaries

Abstract

The industry spent 2024 and 2025 learning how to secure the individual agent. The problem still open in 2026 is securing the handoff: the moment one agent passes work to another and a trust boundary gets crossed without anyone checking it. Consider what happens when Agent A asks Agent B to deploy something to production, or to pull a customer's records. Three questions go unanswered, and they go unanswered at machine speed. Did A really hold the authority it just passed on? Will B end up with more access than it should? And whose human authorization, if anyone's, still sits behind the action four hops down the chain? In most production multi-agent systems today, nobody checks any of the three. This is not a new vulnerability. It is the confused deputy problem, known in distributed systems since 1988, showing up again in a setting that makes it far more dangerous, because agents are autonomous, act asynchronously, delegate recursively, and increasingly cross organizational lines. The defenses built for human-to-service authorization, such as OAuth, SAML and OIDC, carry assumptions that agents break. For a Chief AI Officer the takeaway is uncomfortable but simple.