Without this the store reports nothing trusted on every launch. Safe — known_hosts
still decides, and a host trusted only by us degrades to first contact and is
re-recorded — but it silently discarded our own accept records, so the store the
design calls for was not actually in use.
Bound beside the profile Store, since it is a sidecar of the same data file.
Also records why the paired-web carve-out the migration review asked for is NOT
implemented in Phase 1, rather than leaving it looking forgotten. That carve-out
exists to stop a web client waiting out the 120s prompt timeout — a hang only
reachable if a prompt exists, and Phase 1 has none, which the decision function
pins with a test asserting it never returns 'prompt'. An RPC connect therefore
behaves exactly like a local one. Adding a fail-fast path now would introduce a
failure mode for a hang that cannot occur; it becomes load-bearing when the
dialog lands and is listed under Phase 2.
Noted there for whoever builds Phase 2: runtime/rpc/methods/ssh.ts already
swallows the specific error and rethrows a generic one, so the host-key reason
will not reach a web user without a change there too.
Full unit suite: 52,352 pass. The 8 failures are the known environment baseline
(5 osc8, 2 IME) plus one browser-cookie suite-ordering flake that passes in
isolation — none in src/main/ssh, and none related to this change.
Three things the reviews changed, kept visible rather than quietly edited out.
THREAT MODEL WAS WRONG IN THREE PLACES. Jump hosts are not the worst case — they
are already safe: shouldUseSystemSshTransport branches on exactly the inputs
resolveEffectiveProxy does, and attemptConnect returns after the system probe, so
ProxyJump goes through OpenSSH and is verified. Agent forwarding was overstated
(gated on the user's ForwardAgent). Credential theft was understated: any auth
error counts as agent fallback, so a MITM walks the user to the password AND
private-key passphrase prompts, and cachedPassword replays without prompting. The
relay claim was backwards — the attacker owns their own machine; the real impact
is the return direction, where they become the host our workspace trusts.
TYPE SCOPING IS A DOWNGRADE VECTOR WITHOUT ALGORITHM ORDERING. This was the
decision I flagged as least certain and asked to have argued both ways. OpenSSH
is safe only because order_hostkeyalgs() puts known types first and RFC 4253
gives the client's order priority. ssh2 negotiates ed25519 first regardless, so
an attacker who cannot forge the RSA key on file just presents ed25519 and gets a
friendly first-contact prompt instead of a hard failure. Keep scoping, but set
algorithms.serverHostKey to lead with the types on file — and add a sixth
outcome for 'unknown type, known host', which must never read as first contact.
SHIP THE DEFENCE BEFORE THE DIALOG. Startup restore fires eager connects for all
targets in parallel with a 15s timeout while a prompt would live 120s; ephemeral
VM targets present a new key every launch; paired-web connects run on the host
desktop, so the dialog opens on someone else's screen. Phase 1 is therefore no
modal at all: consult known_hosts and our store, match connects, unknown persists
with accept-new semantics, mismatch and revoked hard-fail. That is the whole MITM
defence with none of the migration risk.
Also folded in, verified live against OpenSSH 10.2p1: the without-port fallback
(bracketed lookup first, then bare, where the second pass can only yield match or
unknown — otherwise a bare line plus a non-default port produces a spurious
prompt); hashed entries hash the candidate form; multiple files union; a
cert-authority line does not match a plain key. IPv6 and bracket parsing moved
INTO scope — that is a parser requirement, not a scope call, and getting it wrong
produces the prompt-training harm the design exists to avoid.
Today's ssh2 verifier records a fingerprint and returns true — every host key is
accepted, with no known_hosts consult and no change detection anywhere in
src/main/ssh/. Scope is per-connection, so exec, SFTP, port forwarding, the
watcher and relay deploy all ride that one unverified handshake, and the
ProxyJump path puts the final hop — the topology most likely to cross untrusted
network — on ssh2 specifically.
Decisions worth calling out:
- Read the user's known_hosts as a trust source but NEVER write to it. That file
is shared with every other SSH tool on the machine; appending means line
endings, permissions, concurrent writers and a corruption blast radius well
beyond us. Accepted keys go to our own per-target store. Reading theirs is also
the entire migration story: most developers already have their hosts there.
- Mismatch is scoped to the SAME key type. A host with only an RSA entry that
presents ed25519 is unknown, not changed. ssh2 negotiates ed25519 first, so
without this we would fire a change-of-key alarm at nearly every existing user
on their first upgraded connect — training them to dismiss the one warning that
is supposed to mean something. Flagged in review as the decision I am least
sure of; a downgrade-vector argument against it is being tested.
- Changed key hard-fails with no override button; recovery is a separate explicit
action, offered only when OUR store is what disagreed, because forgetting our
record cannot unblock a known_hosts conflict.
- Background reconnects deny rather than prompt. A dialog the user cannot place
in context only teaches click-through.
Two traps are documented because either would make the fix silently do nothing:
an async verifier returns a Promise, which ssh2 reads as truthy and accepts
immediately; and the existing test mock invokes hostVerifier with one argument
and ignores the return, so it would pass against a verifier that never decides.
Design only — no behaviour change. The doc is added to the tracked-reference
allowlist in .gitignore alongside the other docs/reference entries.
Neil