# mark3labs mcp-go SSRF and credential leak via unvalidated Location header

Source: https://junglewise.ai/threats/go-2026-6911-ssrf-and-credential-leak-via-unvalidated-location-header-1f243351  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-05. Updated: 2026-11-07  
License: CC BY 4.0 with a link back

Severity: info · Published 2026-11-05

The mcp-go library is a Go SDK for the Model Context Protocol used in AI applications. When an MCP server responds with a redirect, the client automatically follows it to arbitrary destinations while attaching configured authentication credentials and headers, enabling attackers to steal credentials or redirect requests to internal systems. This allows a malicious MCP server to extract API keys, OAuth tokens, or force requests to internal services.

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

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** Informational severity, published 5 November 2026.

**Which products and versions are affected?** github.com/mark3labs/mcp-go (Go) SEMVER:introduced=0; Mark3labs Mcp-Go all versions up to and including v1.5.0.

**Is there a fix for This vulnerability?** 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 This vulnerability attacked?** It is attacked over the network, in a software library.

**Am I affected?** Check whether you run github.com/mark3labs/mcp-go (Go) or 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 NewStreamableHTTP function in github.com/mark3labs/mcp-go/client/transport constructs an HTTP client with a nil CheckRedirect policy, causing it to follow 3xx redirects to any host and scheme. The client attaches OAuth bearer tokens and custom headers via a RoundTripper layer, which are then sent to the redirect target. An MCP server can exploit this by returning a Location header pointing to an attacker-controlled endpoint or internal service, resulting in server-side request forgery (SSRF) and credential disclosure.

## Affected products

- mark3labs mcp-go all versions up to and including v1.5.0

## Timeline

- 2026-11-05: disclosed: Public disclosure via OSV and golang/vulndb

## References

- [https://github.com/golang/vulndb/issues/6911](https://github.com/golang/vulndb/issues/6911)
- [https://github.com/mark3labs/mcp-go/issues/1164](https://github.com/mark3labs/mcp-go/issues/1164)

## Related threats

- [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 denial of service in StreamableHTTPServer.ServeHTTP](https://junglewise.ai/threats/cve-2026-108859-mcp-go-through-1-2-1-contains-a-denial-of-service-vulnerability)
- [mcp-go HTTP Host header validation bypass](https://junglewise.ai/threats/cve-2026-81092-mcp-go-http-host-header-validation-bypass)