Glossary
State Handle Hijacking
An attack where a server-side state identifier (a handle) is obtained or guessed by an attacker and used to access another user's state on an MCP server. Introduced as a named attack surface by MCP's 2026-07-28 statelessness redesign, which removed session-based identity and made handle continuity the server's explicit responsibility instead of the protocol's.
The NSA's May 2026 guidance flagged the underlying design gap directly: associating a session to an identity is not defined by the MCP protocol. A server can authenticate correctly at connection time and still be vulnerable, because that says nothing about whether every later request in the session is still verified as the same user.
Does authenticating a session prevent state handle hijacking?
Not by itself. A server can authenticate correctly when a session starts and still be vulnerable, because MCP's protocol doesn't define whether every later request in that session is re-verified as the same user — that continuity is the server's responsibility to implement, not something the protocol guarantees.
Where this comes up
MCP Security in Production
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