CVE-2026-111768

Name of the Vulnerable Software and Affected Versions @modelcontextprotocol/sdk versions 1.3.0 through 1.31.0 @modelcontextprotocol/server versions 2.0.0 through 2.2.0

Description HTTP servers do not enforce a limit on the number of array elements and object keys validated in a single request. An attacker can send a request within the default 4 MiB size limit containing a validation workload large enough to cause JavaScript heap exhaustion, leading to process termination. This issue primarily affects tools that accept arrays or records and does not impact stdio-only servers. No credentials are required for exploitation unless the application implements authentication before SDK processing.

Recommendations For @modelcontextprotocol/sdk versions 1.3.0 through 1.31.0, upgrade to version 1.32.0 or later, set the maxToolInputElements option in McpServer to a value slightly above the largest required input, and lower the maxRequestBodySize on the transport or createMcpHandler(). For @modelcontextprotocol/server versions 2.0.0 through 2.2.0, upgrade to version 2.3.0 or later, set the maxToolInputElements option in McpServer to a value slightly above the largest required input, and lower the maxRequestBodySize on the transport or createMcpHandler(). As a mitigation for versions prior to @modelcontextprotocol/sdk 1.30.1 or @modelcontextprotocol/server 2.1.0, use a reverse proxy to limit request size.