[BUG] Claude Code automatically opens and gets stuck reading from /dev/ttyACM* devices causing complete lockup

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

## Bug Description
Claude Code automatically discovers and opens /dev/ttyACM* serial
devices for reading, causing complete process lockup when Nordic nRF52840
development boards or similar USB CDC-ACM devices are connected.

## Technical Evidence

• lsof shows: claude [PID] user 24r CHR 166,0 0t0 1764 /dev/ttyACM0
• strace reveals infinite read loop: `read(24, "\\33[m\\33[1;32mble>

\\33[m^;[[mca u \\n", 8192)`

• Claude gets stuck processing corrupted ANSI escape sequences from device

console output

• Process requires kill -9 to terminate

## Environment

• OS: Linux (xubuntu 22.04LTS)
• Claude Version: v1.0.113
• Device: Nordic nRF52840 dongles/dev boards (USB CDC-ACM devices)

## Root Cause
Claude automatically monitors TTY devices it discovers, but cannot
properly handle binary/corrupted console output from embedded development
boards.

## Workarounds Found

### 1. Firejail with --private-dev (WORKING)
```bash
firejail --private-dev claude
Note: Blacklisting individual devices with --blacklist=/dev/ttyACM* still
results in the same lockup. Only --private-dev (which creates an isolated
/dev) works.

1. SSH Process Isolation (WORKING)

Execute all device operations via SSH to localhost for complete process
isolation

1. Permission-based (Alternative)

sudo chmod 600 /dev/ttyACM*

Expected Behavior

Claude should not automatically monitor arbitrary serial devices, or
should gracefully handle binary/corrupted input from such devices.
```

What Should Happen?

claude should continue without lockup / locking the ttyACMs and without the need to jail it.

Error Messages/Logs

Steps to Reproduce

## Steps to Reproduce

1. Connect an nRF52840 development board (or similar USB CDC-ACM device)

to Linux system

1. Verify /dev/ttyACM0 appears
2. Start Claude Code in the same environment
3. Claude process becomes unresponsive and stops processing commands

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

v1.0.113

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Xterm

Additional Information

_No response_