CVE-2026-108859: mcp-go through 1.2.1 Denial of Service via Unbounded POST Body Buffering
mcp-go through 1.2.1 contains a denial of service vulnerability in StreamableHTTPServer.ServeHTTP that allows remote unauthenticated attackers to exhaust memory by sending oversized POST bodies. Attackers can send arbitrarily large or many concurrent POST requests, read fully via io.ReadAll before validation, to degrade or OOM-kill the server process.
Affected Software
Event History
Frequently Asked Questions
Which deployments are exposed?
Deployments using mcp-go through version 1.2.1 that expose StreamableHTTPServer.ServeHTTP to remote clients are exposed. The issue can be reached over the network and does not require authentication or user interaction.
What does an attacker need to do to cause impact?
An attacker can send an oversized POST body, or many concurrent POST requests with large bodies. The handler reads request bodies fully with io.ReadAll before validating them, allowing memory consumption to grow until service degradation or an out-of-memory process termination occurs.
Is confidentiality or data integrity affected?
The reported impact is availability only. The supplied severity vector indicates no confidentiality or integrity impact.