🤖 feat: SSH host-key verification with interactive dialog #2399

ethanndickson · 2026-02-13T02:06:08Z

Summary

End-to-end SSH host-key verification: when connecting to an unknown host, Mux detects the host-key prompt, shows a confirmation dialog with the fingerprint, and pipes the user's yes/no decision back to complete the SSH handshake — replacing the previous StrictHostKeyChecking=no bypass.

Closes #963

Background

Previously Mux disabled host-key checking entirely (StrictHostKeyChecking=no for OpenSSH, hostVerifier: () => true for SSH2). This is a security gap — users should explicitly accept unknown host keys, matching the standard SSH experience.

Implementation

The feature spans three layers:

Backend broker — HostKeyVerificationService deduplicates concurrent prompts for the same host with explicit waiter fanout, auto-rejects after 60s, and exposes oRPC endpoints (getHostKeyVerificationRequests, respondToHostKeyVerification).

SSH_ASKPASS mechanism — sshAskpass.ts creates a per-probe temp directory with a shell script that uses per-request file transactions (prompt.<id>.txt / response.<id>.txt) — no FIFOs or mkfifo. Each askpass invocation gets a unique ID, writes its prompt file, and polls for the matching response file. fs.watch detects new prompt files and handles each independently, so multiple prompts per SSH handshake (e.g., host-key + passphrase) work without deadlock.

Prompt classification — The askpass callback in sshConnectionPool.ts classifies prompts via classifyAskpassPrompt(): host-key prompts route through HostKeyVerificationService; non-host-key prompts (passphrase/password) return empty string immediately with a log warning. Passphrase-protected keys are supported only when already unlocked in SSH agent — in-app passphrase entry is intentionally unsupported.

Probe timeout extension — The connection probe starts with a 10s fast-fail timeout but extends to 60s when a host-key prompt is detected, giving users time to review the fingerprint. SSH2's readyTimeout is also extended to match when host verification is enabled.

Frontend dialog — HostKeyVerificationDialog.tsx polls for pending verification requests and presents the host/fingerprint/key-type for user confirmation.

Timeout scoping — resolvePath() calls acquireConnection() before starting its 10s command timer, so the timer covers only command execution — not the connection wait (which can include a 60s host-key dialog). This matches the existing transferBundleToRemote() pattern.

Shared constant — HOST_KEY_APPROVAL_TIMEOUT_MS (60s) is defined once in src/common/constants/ssh.ts and consumed by the verification service, OpenSSH pool, and SSH2 pool.

Graceful fallback — When no host-key verification UI is available (headless/test/CLI), the probe falls back to StrictHostKeyChecking=no + UserKnownHostsFile=/dev/null so SSH connections don't hang on unattended prompts.

BatchMode=yes — Added to spawnRemoteProcess() as defense-in-depth: if the ControlMaster socket isn't reused and SSH encounters an unexpected prompt, it fails fast instead of hanging.

Responder-capability gating — HostKeyVerificationService now tracks active interactive responders via registerInteractiveResponder()/hasInteractiveResponder(). Transports gate askpass, timeout extensions, and host-key callbacks on actual responder availability — not mere service existence. ORPC subscription lifecycle binds responder leases so headless/test contexts never block on impossible prompts. This fixed integration test timeouts caused by mux-askpass waiting on a non-existent dialog.

FIFO prompt queue — HostKeyVerificationDialog replaces the single-slot pending state with a deduplicated FIFO queue, so concurrent host-key prompts for different hosts are never silently dropped. The subscription cleanup now explicitly calls iterator.return() alongside abort signal to ensure backend responder leases are released.

Runtime-aware stream timeouts — SSH integration tests now use STREAM_TIMEOUT_SSH_MS (25s) instead of the local default (15s) for sendMessageAndWait, matching the per-test timeout differentiation already present.

Validation

make static-check passes
11/11 HostKeyVerificationService unit tests pass (including responder-availability + dedupe timeout regressions)
7/7 sshAskpass unit tests pass (multi-prompt handling, idempotent cleanup, dedup, env vars)
25/25 sshConnectionPool unit tests pass (including prompt classification pattern matching)
SSH integration tests: 8/8 pass in ~10s (previously hung indefinitely on SSH cases due to mux-askpass waiting on non-existent dialog)
Manual testing: connect to unknown host → host-key dialog appears → wait >10s → accept → workspace init succeeds

Generated with mux • Model: anthropic:claude-opus-4-6 • Thinking: xhigh • Cost: $57.38

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src/node/runtime/SSH2ConnectionPool.ts

src/node/services/hostKeyVerificationService.ts

Add end-to-end SSH host-key verification: when connecting to an unknown host, Mux detects the host-key prompt via SSH_ASKPASS, shows a confirmation dialog, and pipes the user's decision back to complete the handshake. - Schema + types (src/common/orpc/schemas/ssh.ts) - Backend broker with dedup and 60s auto-reject (hostKeyVerificationService) - DI wiring through service container and oRPC context - SSH_ASKPASS mechanism with FIFO IPC (sshAskpass.ts) - Probe timeout extension: 10s fast-fail, extends to 60s on host-key prompt - Frontend dialog (HostKeyVerificationDialog.tsx) mounted in App - BatchMode=yes for non-interactive SSH execs (defense-in-depth) - Scoped resolvePath timeout to exclude connection acquisition wait, preventing false timeouts when host-key dialog takes >10s - Removed StrictHostKeyChecking=no from OpenSSH and SSH2 transports

Use static imports instead of dynamic await import() (lint rule). Use direct await instead of expect().resolves (await-thenable lint rule). Make HostKeyVerificationService timeout injectable via constructor parameter (defaults to HOST_KEY_APPROVAL_TIMEOUT_MS) so tests can use a short timeout without module mocking.

ethanndickson · 2026-02-13T03:22:31Z

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src/node/services/serviceContainer.ts

src/browser/components/HostKeyVerificationDialog.tsx

ethanndickson · 2026-02-13T04:59:13Z

@codex review

Addressed both P1 and P2:

P1 (responder availability): HostKeyVerificationService now tracks active interactive responders via registerInteractiveResponder()/hasInteractiveResponder(). Both SSH transports and the ORPC router gate interactive prompts on responder availability — not service existence. Headless/test/CLI contexts auto-accept.
P2 (FIFO queue): HostKeyVerificationDialog uses a deduplicated FIFO queue instead of a single slot, so concurrent multi-host prompts are never dropped.
Integration timeouts: SSH tests now use runtime-appropriate stream timeouts. Full matrix (8/8) passes in ~10s — previously hung indefinitely.

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src/node/runtime/sshAskpass.ts

src/browser/components/HostKeyVerificationDialog.tsx

- Replace readdirSync with async readdir in fs.watch callback - Remove async from test callbacks that don't use await - Replace empty catch callbacks with () => undefined

Call iterator.return() alongside abort signal to ensure the backend subscription finally block runs, releasing responder lease and listener state. Some oRPC iterators don't reliably terminate on abort alone.

ethanndickson · 2026-02-13T05:37:04Z

@codex review

Pushed 5 new commits addressing both P1 findings and the P2 iterator cleanup:

Redesign askpass to per-request file transactions — replaced single-shot FIFO with per-request prompt.<id>.txt/response.<id>.txt files, removing mkfifo dependency
Fail fast on non-host-key askpass prompts — added classifyAskpassPrompt() to route host-key prompts through verification and return empty for credential prompts
Regression tests — 7 new askpass tests (multi-prompt, idempotent cleanup, dedup) + 5 prompt classification tests
Lint fixes — async/readdirSync cleanup
Explicit iterator cleanup — call iterator.return() alongside abort signal in subscription cleanup

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chatgpt-codex-connector · 2026-02-13T05:44:45Z

src/node/services/hostKeyVerificationService.ts

+    }
+
+    // Dedup: if a prompt for this host is already pending, append another waiter
+    const existingId = this.inflightByHost.get(params.host);


Deduplicate host-key prompts by host+port

requestVerification() coalesces pending prompts using only params.host, but the new SSH2 caller sends just resolvedConfig.hostName (no port), so concurrent connections to the same hostname on different ports can be merged into one approval flow. In that case one user decision is applied to both fingerprints, which can incorrectly accept or reject the second connection and defeats per-endpoint host-key verification for multi-port hosts.

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chatgpt-codex-connector · 2026-02-13T05:44:46Z

src/browser/components/HostKeyVerificationDialog.tsx

+    } finally {
+      setResponding(false);
+      setPendingQueue((prev) => prev.filter((item) => item.requestId !== requestId));


Preserve pending prompt when respond RPC fails

The dialog always removes the current request in finally, even if api.ssh.hostKeyVerification.respond() throws (for example during renderer/backend reconnects). That drops the UI prompt while the backend request can still be pending until timeout, so the user cannot retry and the SSH handshake fails despite having clicked accept/reject.

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src/node/runtime/SSH2ConnectionPool.ts Show resolved Hide resolved

src/node/services/hostKeyVerificationService.ts Outdated Show resolved Hide resolved

ethanndickson force-pushed the ethan/host-key-verif branch from 874c3e1 to f3622c3 Compare February 13, 2026 02:13

ethanndickson added 4 commits February 13, 2026 14:21

refactor: extract HOST_KEY_APPROVAL_TIMEOUT_MS shared constant

6dcc8f7

Fix SSH host-key approval timeouts in connection pools

9b0acca

fix host key verification timeout waiter fanout

52eea11

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src/node/services/serviceContainer.ts Show resolved Hide resolved

src/browser/components/HostKeyVerificationDialog.tsx Outdated Show resolved Hide resolved

ethanndickson added 3 commits February 13, 2026 15:56

fix: gate host-key interactive prompts on responder availability

a0724e4

fix: use FIFO queue for host-key verification dialog

eb5a3f6

fix: use runtime-aware stream timeouts in SSH integration tests

d2d6cae

chatgpt-codex-connector bot reviewed Feb 13, 2026

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src/node/runtime/sshAskpass.ts Outdated Show resolved Hide resolved

src/node/runtime/sshAskpass.ts Outdated Show resolved Hide resolved

src/browser/components/HostKeyVerificationDialog.tsx Outdated Show resolved Hide resolved

ethanndickson added 5 commits February 13, 2026 16:24

Redesign ssh askpass to use per-request file transactions

45f0a70

fix: fail fast on non-host-key ssh askpass prompts

f2b6a4a

test: add askpass multi-prompt and prompt classification tests

34d3f14

fix: lint errors in askpass implementation and tests

103383d

- Replace readdirSync with async readdir in fs.watch callback - Remove async from test callbacks that don't use await - Replace empty catch callbacks with () => undefined

fix: explicitly close host-key subscription iterator on cleanup

4b1b239

Call iterator.return() alongside abort signal to ensure the backend subscription finally block runs, releasing responder lease and listener state. Some oRPC iterators don't reliably terminate on abort alone.

chatgpt-codex-connector bot reviewed Feb 13, 2026

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🤖 feat: SSH host-key verification with interactive dialog #2399

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ethanndickson commented Feb 13, 2026 •

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