GHSA-f897-62hf-6gxq: High severity npm/@modelcontextprotocol/hono vulnerability
Summary In affected versions, MCP servers reachable over HTTP put no limit on the size of a POST body or on the number of messages in a JSON-RPC batch. Large requests could exhaust the server's memory, and one long batch could block it from serving anyone else. No credentials were needed, unless your application authenticates requests before they reach the SDK.
Am I affected? Yes, if clients you do not fully trust can reach your server over Streamable HTTP. A body parser such as express.json() does not protect you, because it does not limit batch length. Servers that only use stdio are not affected.
Affected versions:
- @modelcontextprotocol/sdk 1.10.0 through 1.30.0 - @modelcontextprotocol/server 2.0.0 - @modelcontextprotocol/node 2.0.0 - @modelcontextprotocol/hono 2.0.0
Fix Upgrade to:
- 1.x: @modelcontextprotocol/sdk 1.30.1 or later - 2.x: @modelcontextprotocol/server 2.1.0, @modelcontextprotocol/node 2.1.0 and @modelcontextprotocol/hono 2.0.1 or later. Upgrade every one you have installed.
Bodies over 4 MiB now get 413, and batches over 100 messages get 400. If your clients send larger bodies, raise the new maxRequestBodySize option.
If you cannot upgrade yet, cap request body size in a reverse proxy.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/@modelcontextprotocol/honoto a version that resolves this vulnerability.Fixed in 2.0.1 - Upgrade
Upgrade
npm/@modelcontextprotocol/nodeto a version that resolves this vulnerability.Fixed in 2.1.0 - Upgrade
Upgrade
npm/@modelcontextprotocol/serverto a version that resolves this vulnerability.Fixed in 2.1.0 - Upgrade
Upgrade
npm/@modelcontextprotocol/sdkto a version that resolves this vulnerability.Fixed in 1.30.1 - Upgrade
Upgrade
@modelcontextprotocol/sdkto a version that resolves this vulnerability.Fixed in 1.30.1 - Upgrade
Upgrade
@modelcontextprotocol/serverto a version that resolves this vulnerability.Fixed in 2.1.0 - Upgrade
Upgrade
@modelcontextprotocol/nodeto a version that resolves this vulnerability.Fixed in 2.1.0 - Upgrade
Upgrade
@modelcontextprotocol/honoto a version that resolves this vulnerability.Fixed in 2.0.1 - Configuration
If clients send larger request bodies, raise the maxRequestBodySize option.
MCP server maxRequestBodySize - Compensating control
If you cannot upgrade yet, cap HTTP request body size in a reverse proxy.
Event History
Frequently Asked Questions
Does using express.json() prevent this issue?
No. A body parser such as express.json() does not limit the number of messages in a JSON-RPC batch, so it does not prevent a long batch from blocking the server.
Are deployments that use only stdio exposed?
No. Servers that only use stdio are not affected.
Does an attacker need credentials to trigger the resource exhaustion?
Normally, no credentials are required. Credentials may be required if the application authenticates requests before they reach the SDK.
What limits are enforced after upgrading?
Request bodies over 4 MiB receive HTTP 413, and batches containing more than 100 messages receive HTTP 400. Clients that legitimately send larger bodies can use the maxRequestBodySize option.
If multiple affected MCP packages are installed, is updating one sufficient?
No. Upgrade every affected package you have installed. The fixed versions are @modelcontextprotocol/sdk 1.30.1 or later for 1.x, and @modelcontextprotocol/server 2.1.0, @modelcontextprotocol/node 2.1.0, and @modelcontextprotocol/hono 2.0.1 or later for 2.x.