Vulnerability · Published Oct 11, 2026 · Assigned by VulnCheck

CVE-2026-108859mcp-go through 1.2.1 Denial of Service via Unbounded POST Body Buffering

High 7.5

In plain English

A high-severity resource allocation without limits in mcp-go from mark3labs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 46% of all known vulnerabilities).

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.5%top 54.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

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 products (as reported)

Vendor	Product	Versions
mark3labs	mcp-go	0 – through 1.2.1

Weakness: CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://hackmd.io/@1ExmmukzRMWN7B4gQ4W-4Q/mark3labs-mcp-go-streamable-http-unbounded-body third-party-advisory
https://github.com/mark3labs/mcp-go/blob/90d247ed8d45cbb7d71d9a95e112789b78760443/server/streamable_http.go#L405-L411 technical-description
https://github.com/mark3labs/mcp-go product
VulnCheck Advisory: mcp-go through 1.2.1 Denial of Service via Unbounded POST Body Buffering third-party-advisory