CVE-2026-108395: CWE-770: Allocation of Resources Without Limits or Throttling in modelcontextprotocol io.modelcontextprotocol.sdk:mcp

The Model Context Protocol Java SDK (artifact io.modelcontextprotocol.sdk:mcp) contains a resource allocation vulnerability (CWE-770) in its Servlet-based SSE, Streamable HTTP, and Stateless server transports. These components read HTTP request bodies into memory without enforcing maximum size limits, allowing unauthenticated remote clients to stream arbitrarily large POST bodies, including chunked transfer encoding. This can exhaust the Java process heap, causing denial of service. The vulnerability affects versions >=0.8.0 <0.13.0, >=0.13.0 <0.18.4, >=1.0.0 <1.1.4, and >=2.0.0-M1 <2.0.1. The issue is fixed in versions 0.18.4, 1.1.4, and 2.0.1. Authentication, origin or host validation, or upstream request-size limits can mitigate the risk by rejecting malicious requests before processing.

An unauthenticated remote attacker can exploit this vulnerability by sending an arbitrarily large HTTP POST request to the affected server transports, causing the Java process to exhaust its heap memory and become unavailable. This results in a denial of service condition. There is no impact on confidentiality or integrity, only availability is affected.

Fixed versions are available: 0.18.4, 1.1.4, and 2.0.1. Users should upgrade to these versions or later to remediate the vulnerability. Additionally, implementing authentication, origin or host validation, or upstream request-size limits can prevent malicious requests from reaching the vulnerable code. Patch status is confirmed fixed in the stated versions.