---
title: "CVE-2026-108859: mcp-go - Denial of Service"
description: "mcp-go <= 1.2.1 contains a denial of service caused by memory exhaustion in StreamableHTTPServer.ServeHTTP due to reading oversized POST bodies before validation, letting remote unauthenticated attackers degrade or crash the server."
url: https://panop.io/threat-heartbeat/CVE-2026-108859/
---

# CVE-2026-108859 mcp-go - Denial of Service

mcp-go <= 1.2.1 contains a denial of service caused by memory exhaustion in StreamableHTTPServer.ServeHTTP due to reading oversized POST bodies before validation, letting remote unauthenticated attackers degrade or crash the server.

CVSS base score 7.5 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.55% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-108859)

## Details

Type

Denial of Service

Impact

Denial Of Service

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Published

11 October 2026

Updated

15 October 2026

Weakness

[CWE-770](https://cwe.mitre.org/data/definitions/770.html)

## Vendor fix

Update to the latest version of mcp-go.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-108859](https://nvd.nist.gov/vuln/detail/CVE-2026-108859)
- [https://github.com/mark3labs/mcp-go/blob/90d247ed8d45cbb7d71d9a95e112789b78760443/server/streamable\_http.go#L405-L411](https://github.com/mark3labs/mcp-go/blob/90d247ed8d45cbb7d71d9a95e112789b78760443/server/streamable_http.go#L405-L411)
- [https://hackmd.io/@1ExmmukzRMWN7B4gQ4W-4Q/mark3labs-mcp-go-streamable-http-unbounded-body](https://hackmd.io/@1ExmmukzRMWN7B4gQ4W-4Q/mark3labs-mcp-go-streamable-http-unbounded-body)
- [https://www.vulncheck.com/advisories/mcp-go-through-1.2.1-denial-of-service-via-unbounded-post-body-buffering](https://www.vulncheck.com/advisories/mcp-go-through-1.2.1-denial-of-service-via-unbounded-post-body-buffering)
- [https://github.com/mark3labs/mcp-go](https://github.com/mark3labs/mcp-go)

[← All CVEs](https://panop.io/threat-heartbeat/)

## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

Panop answers these inside your environment, for this CVE and every other finding.

[Book a demo](https://panop.io/demo)