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high advisory

Model Context Protocol TypeScript SDK: Denial-of-service via unbounded JSON-RPC payloads

The Model Context Protocol (MCP) TypeScript SDK is vulnerable to remote denial-of-service due to a lack of request body size and JSON-RPC batch length limits, allowing unauthenticated attackers to exhaust server resources.

Triage facts

Revision 1
Applicability
@modelcontextprotocol/sdk (1.10.0-1.30.0), @modelcontextprotocol/server (2.0.0) +2
Evidence
Unknown
Severity
High
Action
Elevated
Sources
1 public source
Freshness
Revision 1Oct 29, 21:02 UTC
Source quality
B2Roughly even chance

The Model Context Protocol (MCP) TypeScript SDK fails to enforce limits on HTTP request body sizes and the number of messages within a JSON-RPC batch. This vulnerability allows an unauthenticated attacker to send excessively large payloads or large batches to an MCP server, leading to memory exhaustion or service unavailability. Deployment configurations utilizing stdio are not affected by this vulnerability.

Impact

Successful exploitation results in a denial-of-service condition, potentially crashing the server or preventing legitimate requests from being processed due to resource exhaustion.

Recommendation

  • Update affected packages immediately to the patched versions:
  • For 1.x environments: Update @modelcontextprotocol/sdk to 1.30.1 or later.
  • For 2.x environments: Update @modelcontextprotocol/server to 2.1.0, @modelcontextprotocol/node to 2.1.0, and @modelcontextprotocol/hono to 2.0.1 or later.
  • If immediate patching is not possible, implement a request body size limit at the reverse proxy or API gateway level to mitigate payload-based exhaustion.
  • Review MCP server configurations to verify if client trust boundaries allow unauthenticated access to HTTP transport endpoints.

Immediate actions

Upgrade vulnerable MCP packages to the specified patched versions

IT Operations 48h

Threat Hunt

Identify MCP endpoints receiving excessively large HTTP POST requests or high-frequency JSON-RPC batch requests

T1499.004 medium medium confidence hunt now

Data: Web server access logs, HTTP request body size metadata

Mitigations

Configure reverse proxy to enforce maximum request body size limits

immediate IT Operations

Denial of service via unbounded payloads