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Public story · 2026-08-07 · high
One of three patched bugs let anyone holding a session ID act as that user, the failure the new spec's design removes.
Why now: The spec revision, HashiCorp's Terraform patch and Codex CLI's opt-in support all landed within the ten days ending August 7.
The Model Context Protocol swapped its stateful session model for stateless request/response on July 28, per the MCP blog's revision notes.
On August 4, HashiCorp shipped three patches for Terraform MCP that show why the change mattered. One flaw hit CVSS 10.0: cross-tenant credential reuse in stateless HTTP mode. Another, CVSS 8.9, cached tool calls under a session ID as the only lookup key. Anyone holding another user's session ID could run tool calls as them, the exact hijack the new per-request identity model removes.
Per Cloudflare's teardown, the required initialize/initialized handshake and the Mcp-Session-Id header are both gone. New Mcp-Method and Mcp-Name headers let gateways and WAFs route MCP traffic without parsing JSON bodies. Deterministic tool and resource ordering plus new ttlMs and cacheScope hints make responses cacheable. Server-initiated elicitation is replaced by Multi Round-Trip Requests, where the server returns an input_required result and the client retries.
Roots, Sampling, Logging, Dynamic Client Registration and the old HTTP+SSE transport are deprecated, with a 12-month minimum removal window. Authorization now requires RFC 8707 resource parameters and RFC 9207 issuer identification.
All four Tier 1 SDKs, TypeScript, Python, Go and C#, supported the spec on day one, July 28. Codex CLI added opt-in support on August 7, days after Anthropic said it's bringing the spec to Claude. HashiCorp's third patch, an 8.6 SSRF bug, shipped in the same Terraform MCP 1.2.0 release.
If you're running Terraform MCP in shared HTTP mode, 1.2.0 isn't optional.
Each link below shares sources, entities, or timing with this story.
The 2026-07-28 Model Context Protocol spec published today, and it removes two things every MCP server currently depends on: the initialize/initialized handshake and the Mcp-Session-Id header. Both are gone. Not deprecated. Gone from the core. (Model Context Protocol Blog) Wha...
The Model Context Protocol's 2026-07-28 revision is the biggest change since the protocol existed. The core is now stateless request/response instead of a bidirectional stateful session. Authorization aligns with OAuth 2.1 and OpenID Connect. MCP Apps and Tasks moved under a v...
If you wrote an MCP server before July, it's on a protocol shape the maintainers have already removed. Not deprecated-with-a-migration-window. Removed from the spec. MCP lead maintainers David Soria Parra and Den Delimarsky published an updated roadmap on August 22, and the re...
You have one week. If you run an MCP server in production, stop what you're doing and read the release candidate. The Model Context Protocol's 2026-07-28 spec is the largest revision since the protocol launched, and the headline is architectural: the initialize/initialized han...
Eighteen days. That's how long you have. The 2026-07-28 MCP specification release candidate removes the session concept from the protocol layer entirely. The initialize / initialized handshake is gone. The Mcp-Session-Id header is gone. Protocol version, client identity, and c...
The final spec closes a ten-week validation window that opened May 21, and it removes session management and handshakes entirely. Concretely: a remote server that previously needed sticky sessions, a shared session store, and gateway deep packet inspection can now sit behind p...
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