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

> A browser-based attacker can exploit missing Host header validation in mcp-go to perform DNS rebinding attacks, accessing local MCP servers to read resources or invoke tools.

- **Severity:** High 7.6 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 27 Aug 2026
- **Updated:** 29 Aug 2026
- **Also known as:** GHSA-8g5x-gj7x-mxgm, RHSA-2026:54874

## What is CVE-2026-81092?

CVE-2026-81092 is a high-severity server-side request forgery vulnerability in mark3labs mcp-go, published on 27 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official 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.

Weakness: CWE-346 (Origin Validation Error)

## Which versions are affected by CVE-2026-81092?


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `tempo3.0` | Red Hat:hummingbird:1 | All versions | 0:3.0.3-0.1.hum1 |

## How do I fix CVE-2026-81092?

Upgrade to a fixed version.

## Is CVE-2026-81092 being exploited?

There is no known exploitation of CVE-2026-81092 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-81092 and fix it if it is affected.

What it is: CVE-2026-81092 is a high-severity server-side request forgery vulnerability in mark3labs mcp-go, published on 27 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-81092 in the wild and no public exploit code.

Affected product: mark3labs mcp-go. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-81092/ (Markdown: https://insights.sbomify.com/CVE-2026-81092/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-81092
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-81092
- OSV: https://osv.dev/vulnerability/CVE-2026-81092

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-81092/
Summaries are generated and may contain mistakes; the official description above is the record.