Bug 2436937 (CVE-2026-25536)

Summary: CVE-2026-25536 @modelcontextprotocol/sdk: @modelcontextprotocol/sdk cross-client data leak
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: dschmidt, erezende, jwong, kshier, mattdavi, omaciel, smcdonal, stcannon, teagle, yguenane
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A data leak by way of a race condition has been discovered in the @modelcontextprotocol/sdk npm library. The cross-client response data leak exists when a single McpServer/Server and transport instance is reused across multiple client connections, most commonly in stateless StreamableHTTPServerTransport deployments. When two or more MCP clients send requests concurrently through a shared server instance, JSON-RPC message ID collisions cause responses to be routed to the wrong client's HTTP connection. Client A can receive response data intended for Client B, and vice versa, even when authorization was correctly enforced on each individual request.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-02-04 22:01:17 UTC
MCP TypeScript SDK is the official TypeScript SDK for Model Context Protocol servers and clients. From version 1.10.0 to 1.25.3, cross-client response data leak when a single McpServer/Server and transport instance is reused across multiple client connections, most commonly in stateless StreamableHTTPServerTransport deployments. This issue has been patched in version 1.26.0.