CVE-2026-108859

HighCVSS 7.5

Published: 11/10/2026(UTC)Updated: 18/10/2026(UTC)Translated: 11/10/2026(UTC)NVD NIST

Exploitation Probability (EPSS)

Low risk

0.55%

45th percentile - higher than 45% of all known CVEs

Summary

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.

Risk Assessment

The risk of memory exhaustion and server crash can lead to service disruption and application unavailability. An attacker can also exploit this vulnerability to conduct DoS attacks on other services.

Recommendation

It is recommended to immediately upgrade mcp-go to a version newer than 1.2.1 and implement limits on POST body size and concurrent requests. Also consider validating data before full read.

Other vulnerabilities in mcp-go

CVE-2026-81092Medium
mcp-go accepted requests on its HTTP transports without checking the Host header. StreamableHTTPServer.ServeHTTP in server/streamable_http.go and SSEServer.ServeHTTP in server/sse.go served any request arriving over a loopback connection regardless of the host it named, and the SSE transport's cross-origin default allowed any origin. A page in a browser could point a controlled name at the loopback address and reach a server listening there, invoking tools and reading resources that the server exposed on the assumption that only local software could connect. No release before 0.56.0 validated the header on either transport; 0.56.0 adds server/http_localhost.go, which rejects a loopback-bound request carrying a host that is not a loopback name, and wires it into both transports.

Original NVD description (English source)

Vulnerability data from NVD (NIST) · CISA KEV · EPSS