CVE-2026-25536: MCP TypeScript SDK could route responses to the wrong client
- Product
- @modelcontextprotocol/sdk (npm)
- CVE
- CVE-2026-25536
- Affected
- >= 1.10.0, <= 1.25.3
- Fixed in
- 1.26.0
Last verified against sources: October 16, 2026
What happened
- According to GitHub Advisory Database's advisory (Feb 4, 2026), reusing one StreamableHTTPServerTransport across client requests, or one server instance across transports, caused a cross-client data leak; both are most common in stateless deployments. [1]
Impact
- JSON-RPC message ID collisions could send one client's responses to another client's connection, for all request types including tools/call and resources/read. [1]
What was done
- Patched in 1.26.0. [1]
How to protect yourself
- Upgrade to 1.26.0, which adds runtime guards that turn silent misrouting into immediate errors. [1]
Sources
- GHSA-345p-7cg4-v4c7 — GitHub Advisory Database
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Corrections
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