[Bug]: Desktop SSH remote reconnect loop opens many short sessions and trips host UFW LIMIT (locks out other SSH) #11287

Summary

On macOS desktop with a remote SSH environment, T3 Code opens a managed local-forward tunnel and then repeatedly starts new short-lived SSH sessions to the same host (~every 40s, often 3 accepts per burst). That is enough to trip a common ufw limit on port 22, after which all SSH from that client IP gets Connection refused — including a normal interactive ssh outside T3.

Killing T3 Code (Alpha) stopped the live tunnel process. Leaving UFW alone and waiting for the limit window to cool restored normal SSH.

Environment

• Client: macOS, T3 Code (Alpha) 0.0.40 (com.t3tools.t3code)
• Remote: Linux (Omarchy), OpenSSH sshd, UFW active with default Omarchy rule:
  • 22/tcp LIMIT IN Anywhere # omarchy-sshd
• SSH target: host alias dell → 192.168.8.57, user agentr (standard ~/.ssh/config)
• Remote T3 port: 3773 (matches DEFAULT_REMOTE_PORT / desktop-managed SSH docs)

Observed client process (while T3 was open)

Exact argv from the Mac (matches packages/ssh/src/tunnel.ts startSshTunnel flags):

ssh -o BatchMode=yes -o ConnectTimeout=10 -p 22 \
  -o ExitOnForwardFailure=yes \
  -o ControlMaster=no -o ControlPath=none -o ControlPersist=no \
  -o ServerAliveInterval=15 -o ServerAliveCountMax=3 \
  -n -N -L 52580:127.0.0.1:3773 agentr@dell

Notes:

• Explicitly disables ControlMaster multiplexing (ControlMaster=no / ControlPath=none).
• Forwards a dynamic local port → remote 127.0.0.1:3773.

Evidence on the SSH host (Europe/Oslo, 2026-09-11)

1. UFW rate-limit rejects from the Mac (192.168.8.58) about every 20s once the limit is hot

Example:

[UFW LIMIT BLOCK] ... SRC=192.168.8.58 DST=192.168.8.57 ... DPT=22 ... SYN

~29 UFW LIMIT BLOCK lines in the 21:30–21:40 window alone. From the client this surfaces as:

ssh: connect to host 192.168.8.57 port 22: Connection refused

(even though sshd is up and listening on 0.0.0.0:22).

2. Interleaved sshd accepts show reconnect bursts (often 3 publickey accepts in the same second), ~every 40s

21:30:43 Accepted publickey ... from 192.168.8.58
21:30:44 Accepted publickey ... from 192.168.8.58
21:30:44 Accepted publickey ... from 192.168.8.58
21:31:24 Accepted ... (×3)
21:32:24 Accepted ... (×3)
21:33:05 Accepted ... (×3)
21:33:45 Accepted ... (×3)
21:34:25 Accepted ... (×3)
21:35:05 Accepted ... (×3)
21:35:46 Accepted ... (×3)
21:36:26 Accepted ... (×3)

Sessions are very short (open then close almost immediately in several cases), which looks like launch/readiness/probe/reconnect work rather than one stable tunnel.

3. User impact

• Interactive ssh dell failed with connection refused while T3 was (or had been) reconnecting.
• Direct ssh agentr@192.168.8.57 could succeed intermittently when under the limit, then fail once LIMIT tripped — same IP/port as the dell Host entry (SSH config was not the bug).
• After quitting T3, the -L …:3773 process was gone; waiting for the UFW window to cool restored SSH.

Expected

• One stable SSH control path / tunnel for a connected remote environment.
• Reconnects should be backoff-bounded and should reuse multiplexing (or otherwise avoid opening multiple new TCP/SSH sessions in a tight loop).
• A flaky readiness probe should not create a connection storm that DoSes the host’s SSH rate limit and locks out the user’s other tools.

Related

• Likely related to reconnect / stale-forward cleanup: SSH reconnects can accumulate stale local-forward processes #4144
• Possibly related: [Bug]: Remote environment stuck reconnecting cannot be disconnected without removing it #9685 (stuck reconnecting)

Suggested directions (non-prescriptive)

• Prefer ControlMaster / multiplexed sessions for launch + tunnel + pairing instead of ControlMaster=no for every SSH child when the host already has a live connection.
• Back off aggressively when tunnel readiness fails or when ssh returns connection refused / UFW-style rejects.
• Cap concurrent SSH children per remote target (the code already has a per-target lock; the host still saw multi-accept bursts).
• Document that ufw limit on 22 + desktop-managed SSH reconnect loops can lock users out of the machine.

Happy to attach more logs if useful.