{"id":"CVE-2026-111770","aliases":["EUVD-2026-117804","GHSA-jm63-cq47-j5jp","ROOT-APP-NPM-CVE-2026-111770"],"status":"published","title":"Model Context Protocol TypeScript SDK: Shared transport or server instances delivered one HTTP client's messages to another","description":"The Model Context Protocol TypeScript SDK provides TypeScript client and server implementations of the Model Context Protocol. From 2.0.0 until 2.3.0 in @modelcontextprotocol/server, applications that shared one stateless HTTP transport or one McpServer or Server instance among multiple clients could deliver responses and notifications to the wrong client. The affected surface is an MCP server reached over HTTP by multiple clients. The trigger is reuse of one stateless transport or server instance. Messages were associated with a connection using only the JSON-RPC request identifier. SDK clients start request identifiers at zero, so collisions occur in normal operation. Cross-client delivery exposes one client's responses and notifications to another client. The issue requires an HTTP endpoint reachable by more than one client and an application that constructs the server or transport once at startup instead of once per request or session. stdio servers and factory-created per-call servers are not affected. Upgrading causes reused instances to fail and therefore requires an application code change. This issue is fixed in @modelcontextprotocol/server 2.3.0.","severity":{"version":"3.1","score":7.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:H","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-12","score":0.00367,"percentile":0.31017,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":true,"fix_available":true},"cwes":["CWE-362"],"published":"2026-10-20T20:07:29Z","modified":"2026-11-06T10:46:30Z","exploits":[{"source":"pocgithub","id":"hahahahahahahahah6/mcp-idprobe","title":"hahahahahahahahah6/mcp-idprobe","date":"2026-10-21","url":"https://github.com/hahahahahahahahah6/mcp-idprobe"}],"fixes":[{"ecosystem":"npm","package":"@modelcontextprotocol/server","fixed_in":["2.3.0"],"sources":["ghsa","osv"]},{"ecosystem":"Root:npm","package":"@modelcontextprotocol/server","fixed_in":["2.0.0-aikido.1","2.0.0-aikido.2"],"sources":["osv"]},{"ecosystem":"Root:npm","package":"@rootio/modelcontextprotocol__server","fixed_in":["2.0.0-root.io.1","2.0.0-root.io.2"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"npm","package":"@modelcontextprotocol/server","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.0.0"},{"fixed":"2.3.0"}]}]},{"source":"osv","ecosystem":"npm","package":"@modelcontextprotocol/server","ranges":[{"type":"SEMVER","events":[{"introduced":"2.0.0"},{"fixed":"2.3.0"}]}]},{"source":"osv","ecosystem":"Root:npm","package":"@modelcontextprotocol/server","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.0.0-aikido.1"},{"fixed":"2.0.0-aikido.2"}]}]},{"source":"osv","ecosystem":"Root:npm","package":"@rootio/modelcontextprotocol__server","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.0.0-root.io.1"},{"fixed":"2.0.0-root.io.2"}]}]}],"products":[{"vendor":"@modelcontextprotocol","product":"server"},{"vendor":"devolutions","product":"server"},{"vendor":"modelcontextprotocol","product":"typescript-sdk"}],"references":[{"url":"https://github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-jm63-cq47-j5jp","tags":["x_refsource_CONFIRM","advisory","web"]},{"url":"https://github.com/modelcontextprotocol/typescript-sdk/pull/2918","tags":["x_refsource_MISC","fix","web"]},{"url":"https://github.com/modelcontextprotocol/typescript-sdk/commit/84804c22e45a662675a198f853b7f00063838a8d","tags":["x_refsource_MISC","fix","web"]},{"url":"https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/1.32.0","tags":["x_refsource_MISC","web"]},{"url":"https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/@modelcontextprotocol/server@2.3.0","tags":["x_refsource_MISC","web"]},{"url":"https://github.com/advisories/GHSA-jm63-cq47-j5jp"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/111xxx/CVE-2026-111770.json","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-111770","tags":["advisory"]},{"url":"https://github.com/modelcontextprotocol/typescript-sdk","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-111770","title":"Model Context Protocol TypeScript SDK: Shared transport or server instances delivered one HTTP client's messages to another","description":"The Model Context Protocol TypeScript SDK provides TypeScript client and server implementations of the Model Context Protocol. From 2.0.0 until 2.3.0 in @modelcontextprotocol/server, applications that shared one stateless HTTP transport or one McpServer or Server instance among multiple clients could deliver responses and notifications to the wrong client. The affected surface is an MCP server reached over HTTP by multiple clients. The trigger is reuse of one stateless transport or server instance. Messages were associated with a connection using only the JSON-RPC request identifier. SDK clients start request identifiers at zero, so collisions occur in normal operation. Cross-client delivery exposes one client's responses and notifications to another client. The issue requires an HTTP endpoint reachable by more than one client and an application that constructs the server or transport once at startup instead of once per request or session. stdio servers and factory-created per-call servers are not affected. Upgrading causes reused instances to fail and therefore requires an application code change. This issue is fixed in @modelcontextprotocol/server 2.3.0.","status":"published","published":"2026-11-05T21:28:00.414Z","modified":"2026-11-05T21:44:49.319Z","cvss":[{"version":"3.1","score":7.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:H","level":"high","assessor":"cna"}],"cwes":["CWE-362"],"updated_at":"2026-11-05T22:55:19.167207Z"}],"euvd":[{"id":"EUVD-2026-117804","description":"The Model Context Protocol TypeScript SDK provides TypeScript client and server implementations of the Model Context Protocol. From 2.0.0 until 2.3.0 in @modelcontextprotocol/server, applications that shared one stateless HTTP transport or one McpServer or Server instance among multiple clients could deliver responses and notifications to the wrong client. The affected surface is an MCP server reached over HTTP by multiple clients. The trigger is reuse of one stateless transport or server instance. Messages were associated with a connection using only the JSON-RPC request identifier. SDK clients start request identifiers at zero, so collisions occur in normal operation. Cross-client delivery exposes one client's responses and notifications to another client. The issue requires an HTTP endpoint reachable by more than one client and an application that constructs the server or transport once at startup instead of once per request or session. stdio servers and factory-created per-call servers are not affected. Upgrading causes reused instances to fail and therefore requires an application code change. This issue is fixed in @modelcontextprotocol/server 2.3.0.","status":"published","published":"2026-11-05T21:28:00Z","modified":"2026-11-05T21:44:49Z","cvss":[{"version":"3.1","score":7.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:H","level":"high"}],"updated_at":"2026-11-05T23:02:20.394374Z"}],"ghsa":[{"id":"GHSA-jm63-cq47-j5jp","title":"MCP  TypeScript server SDK: Shared transport or server instances delivered one HTTP client's messages to another","description":"### Summary\nIn affected versions, an MCP server reached over HTTP could deliver one client's responses and notifications to another client. This happened when clients shared one stateless transport, or one `McpServer` or `Server` instance.\n\nMessages were matched to a connection by JSON-RPC `id` alone. SDK clients number requests from 0, so ids collide in normal use.\n\n### Am I affected?\nYes, if more than one client can reach your HTTP endpoint and your code creates the transport or the server once at startup, instead of once per request or per session. Until this release, the README examples of `@modelcontextprotocol/hono`, `express`, `fastify` and `node` showed that pattern.\n\nAffected versions: `@modelcontextprotocol/server` 2.0.0 through 2.2.0.\n\nNot affected:\n\n- `createMcpHandler()` with a factory that builds a new server on every call\n- stdio servers\n- `@modelcontextprotocol/sdk` 1.26.0 and later\n\n### Fix\nUpgrade to `@modelcontextprotocol/server` 2.3.0 or later.\n\n**You also need to change your code.** The SDK now refuses to be shared, so an affected app fails requests after upgrading: a second `connect()` rejects with `ALREADY_CONNECTED`, and a stateless transport rejects its second request.\n\nChange to one of these:\n\n- **`createMcpHandler()`:** pass a factory that builds a new `McpServer` on every call.\n- **Per request:** build a new `McpServer` and a new transport inside the request handler.\n- **Per session:** set `sessionIdGenerator` and keep one `McpServer` and one transport per session.\n\nIf you cannot upgrade yet, the same change fixes affected versions.","status":"published","published":"2026-10-20T20:07:29Z","modified":"2026-10-20T20:08:02Z","cvss":[{"version":"3.1","score":7.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:H","level":"high"}],"cwes":["CWE-362"],"updated_at":"2026-11-02T14:41:33.669646Z"}],"nvd":[{"id":"CVE-2026-111770","description":"The Model Context Protocol TypeScript SDK provides TypeScript client and server implementations of the Model Context Protocol. From 2.0.0 until 2.3.0 in @modelcontextprotocol/server, applications that shared one stateless HTTP transport or one McpServer or Server instance among multiple clients could deliver responses and notifications to the wrong client. The affected surface is an MCP server reached over HTTP by multiple clients. The trigger is reuse of one stateless transport or server instance. Messages were associated with a connection using only the JSON-RPC request identifier. SDK clients start request identifiers at zero, so collisions occur in normal operation. Cross-client delivery exposes one client's responses and notifications to another client. The issue requires an HTTP endpoint reachable by more than one client and an application that constructs the server or transport once at startup instead of once per request or session. stdio servers and factory-created per-call servers are not affected. Upgrading causes reused instances to fail and therefore requires an application code change. This issue is fixed in @modelcontextprotocol/server 2.3.0.","status":"published","published":"2026-11-05T22:17:45.817Z","modified":"2026-11-12T20:04:52.377Z","cvss":[{"version":"3.1","score":7.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:H","level":"high","assessor":"secondary"}],"cwes":["CWE-362"],"updated_at":"2026-11-12T21:32:42.561523Z"}],"osv":[{"id":"CVE-2026-111770","title":"Model Context Protocol TypeScript SDK: Shared transport or server instances delivered one HTTP client's messages to another","description":"The Model Context Protocol TypeScript SDK provides TypeScript client and server implementations of the Model Context Protocol. From 2.0.0 until 2.3.0 in @modelcontextprotocol/server, applications that shared one stateless HTTP transport or one McpServer or Server instance among multiple clients could deliver responses and notifications to the wrong client. The affected surface is an MCP server reached over HTTP by multiple clients. The trigger is reuse of one stateless transport or server instance. Messages were associated with a connection using only the JSON-RPC request identifier. SDK clients start request identifiers at zero, so collisions occur in normal operation. Cross-client delivery exposes one client's responses and notifications to another client. The issue requires an HTTP endpoint reachable by more than one client and an application that constructs the server or transport once at startup instead of once per request or session. stdio servers and factory-created per-call servers are not affected. Upgrading causes reused instances to fail and therefore requires an application code change. This issue is fixed in @modelcontextprotocol/server 2.3.0.","status":"published","published":"2026-11-05T21:28:00.414Z","modified":"2026-11-07T02:48:21.881258249Z","cvss":[{"version":"3.1","score":7.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:H","level":"high"}],"cwes":["CWE-362"],"updated_at":"2026-11-07T03:08:00.544003Z"},{"id":"GHSA-jm63-cq47-j5jp","title":"MCP  TypeScript server SDK: Shared transport or server instances delivered one HTTP client's messages to another","description":"### Summary\nIn affected versions, an MCP server reached over HTTP could deliver one client's responses and notifications to another client. This happened when clients shared one stateless transport, or one `McpServer` or `Server` instance.\n\nMessages were matched to a connection by JSON-RPC `id` alone. SDK clients number requests from 0, so ids collide in normal use.\n\n### Am I affected?\nYes, if more than one client can reach your HTTP endpoint and your code creates the transport or the server once at startup, instead of once per request or per session. Until this release, the README examples of `@modelcontextprotocol/hono`, `express`, `fastify` and `node` showed that pattern.\n\nAffected versions: `@modelcontextprotocol/server` 2.0.0 through 2.2.0.\n\nNot affected:\n\n- `createMcpHandler()` with a factory that builds a new server on every call\n- stdio servers\n- `@modelcontextprotocol/sdk` 1.26.0 and later\n\n### Fix\nUpgrade to `@modelcontextprotocol/server` 2.3.0 or later.\n\n**You also need to change your code.** The SDK now refuses to be shared, so an affected app fails requests after upgrading: a second `connect()` rejects with `ALREADY_CONNECTED`, and a stateless transport rejects its second request.\n\nChange to one of these:\n\n- **`createMcpHandler()`:** pass a factory that builds a new `McpServer` on every call.\n- **Per request:** build a new `McpServer` and a new transport inside the request handler.\n- **Per session:** set `sessionIdGenerator` and keep one `McpServer` and one transport per session.\n\nIf you cannot upgrade yet, the same change fixes affected versions.","status":"published","published":"2026-10-20T20:07:29Z","modified":"2026-10-20T20:15:05.217388038Z","cvss":[{"version":"3.1","score":7.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:H","level":"high"}],"cwes":["CWE-362"],"updated_at":"2026-11-02T15:46:50.687609Z"},{"id":"ROOT-APP-NPM-CVE-2026-111770","title":"CVE-2026-111770 in @modelcontextprotocol/server - Patched by Root","description":"Root has patched CVE-2026-111770 in the @modelcontextprotocol/server package for Root:npm. Multiple fixed versions available.","status":"published","published":"2026-10-30T06:36:19Z","modified":"2026-10-30T07:15:13.355586128Z","updated_at":"2026-11-02T15:53:27.362922Z"}]}}