Is CVE-2026-81092 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-81092 being exploited in the wild.

How severe is CVE-2026-81092?

Medium severity, with a CVSS score of 6.8, published 27 August 2026.

Which products and versions are affected?

Mark3labs Mcp-Go before 0.56.0.

Is there a fix for CVE-2026-81092?

A patch was published on 2026-07-08: Fix merged in PR #921; available in 0.56.0 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-81092 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-81092?

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.

CVE-2026-81092: mcp-go HTTP Host header validation bypass

CVE-2026-81092 · Severity: medium · CVSS 6.8 · Published 2026-08-27

mcp-go is a Go implementation of the Model Context Protocol (MCP), used to integrate language model applications with external tools and data sources. The library accepted HTTP requests on its loopback transports without validating the Host header, allowing an attacker to use DNS rebinding or browser-based attacks to access local tools and resources that should only be available to local software. This could lead to unauthorized tool invocation and data exposure.

Technologies: Mark3labs Mcp-Go. Vendors: Mark3labs.

Quick answers

Is CVE-2026-81092 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-81092 being exploited in the wild.
How severe is CVE-2026-81092?: Medium severity, with a CVSS score of 6.8, published 27 August 2026.
Which products and versions are affected?: Mark3labs Mcp-Go before 0.56.0.
Is there a fix for CVE-2026-81092?: A patch was published on 2026-07-08: Fix merged in PR #921; available in 0.56.0 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-81092 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-81092?: 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 vulnerability is a DNS rebinding / Host header bypass in mcp-go's HTTP transports (StreamableHTTPServer.ServeHTTP in server/streamable_http.go and SSEServer.ServeHTTP in server/sse.go). Both handlers accepted any request arriving over a loopback connection (127.0.0.1, ::1) without validating that the Host header matches a loopback name, and the SSE transport's cross-origin defaults allowed any origin. An attacker can craft a malicious web page that points a domain name under their control at 127.0.0.1 and invoke the target server's HTTP endpoints, bypassing the assumption that only local software can connect. Versions before 0.56.0 are vulnerable; 0.56.0 adds server/http_localhost.go which validates loopback Host headers and rejects non-loopback names on loopback-bound connections.

Affected products

mark3labs mcp-go before 0.56.0

Timeline

2026-08-27: disclosed
2026-07-08: patched: Fix merged in PR #921; available in 0.56.0

References

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