CVE-2026-35577 Missing Host Header Validation in Apollo MCP Server for Localhost Deployments
Attackers can bypass same-origin policy via DNS rebinding to invoke tools on local Apollo MCP servers lacking Host header validation.
- 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
- None listed
What is CVE-2026-35577?
CVE-2026-35577 is a medium-severity vulnerability in apollographql apollo-mcp-server, published on 9 Apr 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
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.
Weakness: CWE-346
Which versions are affected by CVE-2026-35577?
It affects 1 product.
Products include Apollographql Apollo Mcp Server.
How do I fix CVE-2026-35577?
No fix has been published for CVE-2026-35577 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-35577 being exploited?
There is no known exploitation of CVE-2026-35577 in the wild and no public exploit code.
Sources
Also known as GHSA-wqrj-vp8w-f8vh.