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CVE-2026-81092— mcp-go before 0.56.0 Missing Host Header Validation Enables DNS Rebinding

Quick assessment

Affected
mark3labs mcp-go
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

mcp-go 在其 HTTP 传输层处理请求时，未对 Host 头进行校验。具体而言， 中的 和 中的 会响应任何经由回环地址（loopback）到达的请求，而不管请求中声明的主机名是什么。此外，SSE 传输层允许来自任意源（cross-origin default allowed any origin）。 因此，浏览器中的网页可以控制一个自定义的主机名，并将其指向监听在本地回环地址上的服务器，从而调用该服务器暴露的工具并读取资源——而这些资源原本是基于“只有本地软件才能连接”的假设而公开的。 在 0.56.0 之

CVSS 6.8 · Medium

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
mark3labs mcp-go < 0.56.0 affected
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I. Basic Information for CVE-2026-81092

Vulnerability Information
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Vulnerability Title
mcp-go before 0.56.0 Missing Host Header Validation Enables DNS Rebinding
Source: CVE Program / CVE List V5
Vulnerability Description
mcp-go accepted requests on its HTTP transports without checking the Host header. StreamableHTTPServer.ServeHTTP in server/streamable_http.go and SSEServer.ServeHTTP in server/sse.go served any request arriving over a loopback connection regardless of the host it named, and the SSE transport's cross-origin default allowed any origin. A page in a browser could therefore point a name it controlled at the loopback address and reach a server listening there, invoking tools and reading resources that the server exposed on the assumption that only local software could connect. No release before 0.56.0 validated the header on either transport; 0.56.0 adds server/http_localhost.go, which rejects a loopback-bound request carrying a host that is not a loopback name, and wires it into both transports.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
源验证错误
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
mark3labs mcp-go 0 ~ 0.56.0 -

II. Public POCs for CVE-2026-81092

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III. Intelligence Information for CVE-2026-81092

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Patches & Fixes for CVE-2026-81092 (1)

Vendor Advisories for CVE-2026-81092 (1)

Vendor Pages for CVE-2026-81092 (1)

IV. Related Vulnerabilities

Same weakness: CWE-346

V. Comments for CVE-2026-81092

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