The vulnerability in mcp-go (versions up to 1.2.1) is an unbounded POST body buffering flaw that allows an attacker to exhaust server memory. By sending arbitrarily large or multiple concurrent POST requests, the server reads the entire body before validation, causing out‑of‑memory conditions and a denial of service. This flaw is classified as CWE-770.

Affected systems include any deployment of the mark3labs mcp-go server version 1.2.1 or earlier. There is no evidence that later releases contain the fix, so all current installations in that version range are vulnerable. The vendor is mark3labs and the product is mcp-go.

The CVSS score of 8.7 denotes high severity, and although the EPSS score is not available, the remote unauthenticated nature of the flaw suggests a realistic chance of exploitation. The flaw is not listed in the CISA KEV catalog, but attackers can trigger it by sending large HTTP POST bodies directly to the StreamableHTTPServer.ServeHTTP endpoint. Consequences include service disruption and potential denial of the entire application.