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HighVulnerabilityGHSA-f897-62hf-6gxqupdated 27 Oct 2026, 19:02 UTC

MCP SDK servers over HTTP can be overwhelmed by oversized requests

A malicious or careless client can send huge requests or very long batches of messages to an MCP server exposed over HTTP. This can use up the server's memory and stop it from serving other users.

Fix availableOfficial source
SeverityHighCVSS 7.5 of 10
Being exploited?UnclearNo reports either way yet
Fix available?Yes@modelcontextprotocol/sdk 1.30.1 or later; @modelcontextprotocol/server 2.1.0; @modelcontextprotocol/node 2.1.0; @modelcontextprotocol/hono 2.0.1 or later. Fixed versions return 413 for bodies over 4 MiB and 400 for batches over 100 messages. · since 27 Oct 2026
How sure is this?Official sourceBacked by an official source

How the attack works simplified

  1. 1Attacker sends requestsOversized POST body or huge batch
  2. 2Request reaches serverStreamable HTTP endpoint is exposed
  3. 3No size limit appliedSDK accepts the full request
  4. 4Memory exhaustedLong batch blocks other requests
  5. ResultServer crashes or stops serving users

What happened

The MCP TypeScript SDK packages (sdk, server, node, hono) do not limit POST body size or the number of messages in a JSON-RPC batch over Streamable HTTP, enabling memory exhaustion and denial of service.

Why it is dangerous: Any server reachable over HTTP by clients you do not fully trust can crash or stall, blocking all other users. No credentials are needed unless your application authenticates requests before they reach the SDK.

Are you affected?

You are affected if you run an MCP server using Streamable HTTP that untrusted clients can reach, with @modelcontextprotocol/sdk 1.10.0 through 1.30.0, or @modelcontextprotocol/server, @modelcontextprotocol/node 2.0.0, or @modelcontextprotocol/hono 2.0.0.

Package / productAffected versionsFixed in
@modelcontextprotocol/sdk · npm>= 1.10.0, < 1.30.11.30.1
@modelcontextprotocol/server · npm>= 2.0.0, < 2.1.02.1.0
@modelcontextprotocol/node · npm>= 2.0.0, < 2.1.02.1.0
@modelcontextprotocol/hono · npm>= 2.0.0, < 2.0.12.0.1

What to do

  1. Upgrade @modelcontextprotocol/sdk to 1.30.1 or later, or the 2.x packages (server and node to 2.1.0, hono to 2.0.1) if you use them
  2. Upgrade every MCP package you have installed, not just one
  3. If you cannot upgrade yet, set a maximum request body size in a reverse proxy in front of the server
  4. If legitimate clients send larger bodies, raise the new maxRequestBodySize option after upgrading

Timeline

  1. 27 Oct 2026, 19:02 UTC
    Publicly disclosed
  2. 27 Oct 2026, 19:02 UTC
    Reported by GitHub Advisory · GitHub Advisory
  3. 27 Oct 2026, 19:02 UTC
    Picked up by Zero Radar

Sources 1 report, oldest first

Official vendor, government CERT or advisory database

Technical details

ID
GHSA-f897-62hf-6gxq
CVSS
7.5 / 10
Disclosed
27 Oct 2026, 19:02 UTC
On Zero Radar
27 Oct 2026, 19:02 UTC (1 min after disclosure)
Last change
27 Oct 2026, 19:02 UTC

The plain-language parts and the attack diagram were written by an AI model (anthropic/claude-haiku-5.5) from the sources above. Facts like versions, exploitation and dates come from the sources themselves. How Zero Radar works

MCP SDK servers over HTTP can be overwhelmed by oversized requests · Zero Radar