Security hardening: MCP server auth#540
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Pull request overview
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Adds security hardening for MCP integrations by introducing opt-in MCP server authentication and default URL validation to mitigate client-side SSRF risks.
Changes:
- Add
requireAuthhook toMcpPluginto gate inbound MCP/mcprequests with 401 on failure. - Add
validateMcpServerUrlURL gate (scheme + DNS/private-network filtering) and exposeallowPrivateNetwork/validateUrlparams in the MCP client. - Add/adjust Jest tests to cover URL validation and server auth behavior.
Reviewed changes
Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.
Show a summary per file
| File | Description |
|---|---|
| external/mcpclient/src/url-validation.ts | Implements default URL scheme + private-network/DNS-based validation and error type. |
| external/mcpclient/src/url-validation.spec.ts | Adds unit tests for URL validation behavior and edge cases. |
| external/mcpclient/src/mcp-client-types.ts | Extends client params with allowPrivateNetwork and validateUrl. |
| external/mcpclient/src/mcp-client-plugin.ts | Wires URL validation into MCP client creation flow. |
| external/mcpclient/src/mcp-client-plugin.spec.ts | Stubs DNS lookup to keep existing tests deterministic/offline. |
| external/mcp/src/plugin.ts | Adds requireAuth option, startup warning, and auth middleware for MCP SSE route prefix. |
| external/mcp/src/plugin.spec.ts | Adds unit tests for new checkAuth behavior with various outcomes. |
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corinagum
changed the title
Per team decision, the MCP client SSRF guard adds friction for legitimate on-prem MCP customers and the underlying risk is low-likelihood. Reverting the client-side URL validation work; the McpPlugin server auth (#14) and the Express-level path-prefix middleware refactor are kept. Removes: - external/mcpclient/src/url-validation.ts (and spec) - McpClientPluginParams.allowPrivateNetwork + validateUrl - validateMcpServerUrl call in makeMcpClient - DNS mock added to mcp-client-plugin.spec.ts
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In checkAuth, after the requireAuth try/catch, return early without writing a 401 if req.aborted is set. The client has already disconnected; attempting to set headers on a destroyed stream produces noisy warnings without changing observable behavior. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
lilyydu
approved these changes
May 7, 2026
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Summary
Addresses security scan finding #14 (MCP server mounted without auth). TypeScript half of a 2-SDK PR set (.NET PR is on the same branch name).
#14 — MCP server auth
New opt-in
requireAuthhook onMcpPluginOptions:Hook is called once per inbound MCP request via an Express-level prefix middleware on
/mcp(covers any current or future handler registered under that path).false/throw returns 401. When unset, all requests are accepted and a one-time startup warning fires when the SSE transport comes up.Design doc
design/mcp-server-auth-options.mdE2E verified
/mcpreturns 401 without auth, SSE handshake on correct bearer/api/messages): bot responded to a devtools chat message withREQUIRE_AUTH=1active simultaneouslyrequireAuthis unset; silent when set