Model Context Protocol TypeScript SDK: Memory exhaustion via array and object validation (CVE-2026-111768)

The Model Context Protocol (MCP) TypeScript SDK, specifically the @modelcontextprotocol/sdk (versions 1.3.0 to 1.31.0) and @modelcontextprotocol/server (versions 2.0.0 to 2.2.0) packages, contains a memory exhaustion vulnerability (CVE-2026-111768). The SDK fails to impose validation limits on the number of array elements and object keys processed during an incoming HTTP request. An attacker can craft an HTTP request that stays within the default 4 MiB size limit but contains a highly complex or deeply nested structure, forcing the server to consume excessive memory during parsing. This results in a JavaScript heap out of memory error, causing the MCP server process to crash. This vulnerability is primarily exploitable in environments where the MCP server is exposed via HTTP to untrusted clients, such as tools configured using McpServer.

Impact

Successful exploitation results in a denial-of-service (DoS) condition, rendering the affected MCP server process unavailable. This impacts applications and services relying on MCP servers for tool execution and data exchange. Infrastructure utilizing internet-facing MCP servers is at the highest risk, as the vulnerability does not require authentication unless implemented manually before the request reaches the SDK.

Recommendation

1. Upgrade to the patched versions immediately: @modelcontextprotocol/sdk to 1.32.0 or later, and @modelcontextprotocol/server to 2.3.0 or later.
2. Implement the maxToolInputElements option when initializing McpServer to limit the number of elements and keys in tool arguments.
3. Restrict request sizes by configuring maxRequestBodySize on the transport or createMcpHandler(), or by setting limits on front-end reverse proxies or body parsers (e.g., Express or Fastify) if the SDK upgrade is not immediately possible.
4. Audit network exposures for all MCP-based services to ensure they are not unnecessarily exposed to untrusted internet traffic.