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* 🔌 fix: Follow 307/308 redirects in MCP streamable HTTP transport Some MCP servers (e.g. Coda) return 308 Permanent Redirect to route doc-scoped tool calls to a different endpoint path. The fetch wrapper used `redirect: 'manual'` for SSRF protection, which silently dropped these redirects and caused tool calls to fail with empty error bodies. Follow 307/308 redirects (method-preserving per RFC 7538) up to a depth of 5. SSRF safety is preserved because the same undici Agent with its SSRF-safe connect function validates redirect targets. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> * 🛡️ fix: Harden MCP 307/308 redirect handling against SSRF and credential leaks - Validate every redirect target against `resolveHostnameSSRF` so allowlist deployments (which disable connect-time SSRF protection) still block hops to private/reserved IPs. - Strip `Authorization`, `Cookie`, `mcp-session-id`, and any user-injected headers when a 307/308 crosses an origin boundary, mirroring browser/Fetch behavior so a redirecting MCP server can't exfiltrate credentials. - Cancel the intermediate response body before each next hop so undici can reuse pooled sockets rather than holding them until GC. - Restructure redirect test helpers to be same-origin (matching real-world Coda-style routing), drop dead setup code, fix the misleading "5 hops successfully" test, and add coverage for SSRF-blocked redirects, cross- origin credential stripping, and same-origin credential preservation. * 🛡️ fix: Also strip `serverConfig.headers` on cross-origin MCP redirects Previously only runtime `setRequestHeaders` keys were treated as secret on a 307/308 cross-origin hop. API keys baked into `serverConfig.headers` (passed through `requestInit.headers` at transport construction time) survived stripping, so a malicious MCP endpoint could exfiltrate them by returning a cross-origin `Location`. Pass the configured header keys through to `createFetchFunction` so both runtime and config secrets are stripped. The cross-origin credential test now also configures `serverConfig.headers` to lock in this behavior. * 🧹 chore: Tighten MCP redirect-stripping coverage and helper duplication - Add `proxy-authorization` to the cross-origin forbidden header set so a forward-proxy credential header would also be stripped on a cross-origin hop, matching the Fetch-spec list. - Strengthen the cross-origin credential test with positive assertions that benign protocol headers (`accept`, `content-type`) survive the hop, so a regression that strips everything indiscriminately would now fail. - Extract the duplicated MCP request handler / session-teardown logic from three test helpers into shared `createMCPRequestHandler` and `closeMCPSessions` utilities. * 🛠️ fix: Handle `Request` inputs in MCP `customFetch` URL derivation `customFetch` is typed to accept `UndiciRequestInfo` (`string | URL | Request`), but `Request.prototype.toString()` returns `"[object Request]"`. The previous implementation derived `originalOrigin` and the redirect base via `url.toString()`, so a `Request` input would throw inside `new URL(...)` before any network call — a regression even when no redirect was involved. Add a `getRequestUrlString` helper that extracts the URL string for all three shapes, track the URL string alongside the fetch input through the redirect loop, and add parameterized tests that exercise `customFetch` with each shape. * 🛠️ fix: Don't override `Request` input headers in MCP `buildFetchInit` Previously `buildFetchInit` always set `headers` on the returned init — even when neither `init.headers` nor runtime headers contributed anything. Passing `headers: {}` to `undiciFetch` overrides the headers carried on a `Request` input (auth tokens, MCP session, protocol negotiation), so Request-based wrappers could fail authentication even without a redirect in play. Skip the `headers` override entirely when there is nothing to merge. Adds a regression test that supplies `Authorization` and a custom header on the `Request` itself and asserts both reach the target server. * 🛠️ fix: Preserve `Request` method/body across MCP redirects + guard cross-origin strip Two regressions surfaced by extending `customFetch` to accept `Request` inputs: 1. **307/308 method/body loss.** The redirect loop switches `url` to the new `Location` string, but the original `Request`'s method and body stayed bound to the (now-discarded) `Request` object. A redirected POST silently became a GET with no payload — the exact behavior the method-preserving codes are designed to prevent. Added a `resolveFetchInput` helper that runs once at the top of `customFetch`, extracts a `Request`'s method/body/headers into the shared init, and buffers the body via `arrayBuffer()` so 307/308 retries can replay it. 2. **Cross-origin strip crashed on absent headers.** After the previous fix that stopped `buildFetchInit` from setting `headers: {}`, `currentInit.headers` could legitimately be `undefined`. The cross-origin branch read it as a `Record` and called `Object.entries` on `undefined`, throwing `TypeError`. Guard the branch on `currentInit.headers != null` — when there are no headers there is nothing to strip. Adds two regression tests: a POST-with-body `Request` that 308-redirects cross-origin (asserts both method and body survive) and a no-headers cross-origin redirect (asserts the strip path no longer crashes). * 🛠️ fix: Forward `Request.signal` through MCP `customFetch` normalization `resolveFetchInput` was copying method/body/headers off a `Request` input but dropping `Request.signal` on the floor, so a caller that wired an `AbortController` onto the `Request` for cancellation/timeouts lost that wiring as soon as we re-shaped the input into the `(string, init)` pair used by the redirect loop. Subsequent aborts no longer reached the in-flight fetch — a regression from the pre-PR code, which forwarded the original `Request` directly to undici. Forward the signal alongside method/body/headers, with explicit `init.signal` still winning per Fetch-spec semantics. Regression test aborts a controller before calling \`customFetch\` with the wired `Request` and asserts the call rejects. * 🧪 test: Pin URL.origin contract for protocol-downgrade redirect handling Audit follow-up. The cross-origin strip path keys off `targetUrl.origin !== originalOrigin`, and `URL.origin` is defined as `scheme + "://" + host + ":" + port`, so a same-host `https → http` redirect produces a different origin and trips the strip path through the existing logic — no separate code path needed. Pin that contract with a small unit test so a future change to URL semantics (or a refactor that swaps in a different comparison) doesn't silently regress protocol-downgrade stripping. Standing up a TLS fixture (self-signed cert, undici skip-verify, etc.) just to re-prove the URL spec is wasted complexity. --------- Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Co-authored-by: Danny Avila <danny@librechat.ai> |
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