# CVE-2026-108859: mcp-go denial of service in StreamableHTTPServer.ServeHTTP

Source: https://junglewise.ai/threats/cve-2026-108859-mcp-go-through-1-2-1-contains-a-denial-of-service-vulnerability  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-11. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2026-108859 · Severity: high · CVSS 7.5 · Published 2026-10-11

mcp-go is a Go implementation of the Model Context Protocol used to integrate language model applications with external data sources. A remote attacker can send oversized HTTP POST requests to exhaust the server's memory, causing it to crash or become unresponsive without requiring authentication.

Technologies: [Mark3labs Mcp-Go](https://junglewise.ai/threats/technologies/mcp-go). Vendors: [Mark3labs](https://junglewise.ai/threats/vendors/mark3labs).

## Quick answers

**Is CVE-2026-108859 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-108859 being exploited in the wild.

**How severe is CVE-2026-108859?** High severity, with a CVSS score of 7.5, published 11 October 2026.

**Which products and versions are affected?** Mark3labs Mcp-Go through 1.2.1.

**Is there a fix for CVE-2026-108859?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-108859 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-108859?** Check whether you run Mark3labs Mcp-Go at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The StreamableHTTPServer.ServeHTTP handler reads the entire POST request body using io.ReadAll before validating the content size, allowing attackers to send arbitrarily large or many concurrent requests to exhaust memory. The vulnerability requires network access but no authentication or user interaction. An attacker gains the ability to trigger out-of-memory conditions and deny service.

## Affected products

- mark3labs mcp-go through 1.2.1

## Timeline

- 2026-10-11: disclosed

## References

- [https://github.com/mark3labs/mcp-go](https://github.com/mark3labs/mcp-go)
- [https://github.com/mark3labs/mcp-go/blob/90d247ed8d45cbb7d71d9a95e112789b78760443/server/streamable_http.go](https://github.com/mark3labs/mcp-go/blob/90d247ed8d45cbb7d71d9a95e112789b78760443/server/streamable_http.go)

## Related threats

- [mark3labs mcp-go SSRF and credential leak via unvalidated Location header](https://junglewise.ai/threats/go-2026-6911-ssrf-and-credential-leak-via-unvalidated-location-header-1f243351)
- [Mark3labs mcp-go improper validation in OAuthHandler](https://junglewise.ai/threats/cve-2026-123272-mark3labs-mcp-go-before-v1-2-1-contains-an-improper-validation)
- [mcp-go HTTP Host header validation bypass](https://junglewise.ai/threats/cve-2026-81092-mcp-go-http-host-header-validation-bypass)