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.

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.

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

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. Vendors: Go, 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

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