Access Control

Limit what authenticated users can actually do. Even with valid credentials, users can only reach destinations you allow, run commands you whitelist, and access files in directories you specify.

Three Layers of Restriction

Layer	What It Controls	Configuration
Exit routes	Which IP ranges/domains traffic can reach	Exit Configuration
Shell whitelist	Which commands can be executed	Shell Configuration
File paths	Which directories are accessible	File Transfer Configuration

Route-Based Access Control

Exit nodes only forward traffic to destinations that match their advertised routes. This provides implicit access control:

• Advertise 10.0.0.0/8 = only internal network accessible
• Advertise specific IPs = only those servers reachable
• Don't advertise 0.0.0.0/0 = no internet access

How Route ACL Works

1. Client connects to destination via SOCKS5
2. Ingress agent routes to exit agent
3. Exit agent checks if destination matches advertised routes
4. No match: Connection rejected with "no route" error
5. Match: Connection established

Route ACL Patterns

Pattern	Effect
Internal CIDRs only	Block all internet access
Specific host IPs	Whitelist individual servers
Split exits	Different exits for internal vs. external
Domain routes	Control access by hostname

Configuration

See Exit Configuration for route setup including CIDR and domain routes.

Shell Command Whitelist

The shell whitelist determines which commands can be executed remotely:

Whitelist Setting	Behavior
[] (empty)	No commands allowed (default)
["whoami", "hostname"]	Only listed commands
["*"]	All commands (dangerous!)

Whitelist Principles

• Command names only: whoami, not /usr/bin/whoami
• Arguments not restricted: ls -la / works if ls is whitelisted
• Case-sensitive: Must match exactly

Safe Commands for Monitoring

System info: whoami, hostname, uptime, uname Network diagnostics: ip, ping, traceroute, dig Resource monitoring: df, du, ps, top, free

Commands to Avoid

• System modification: rm, mv, cp, chmod, chown
• Code execution: sh, bash, python, perl, eval
• Data access: cat, less, grep, find
• Privilege escalation: sudo, su

Configuration

See Remote Shell Configuration for whitelist setup.

File Path Restrictions

File transfers are restricted to allowed directories:

Setting	Behavior
[] (empty)	No paths allowed (default)
["/tmp", "/data"]	Only listed paths and subdirectories
["*"]	All paths (dangerous!)

Path Matching

Paths must start with an allowed prefix:

• /tmp allows /tmp/file.txt and /tmp/subdir/file.txt
• Path traversal is blocked: /tmp/../etc/passwd is rejected

Configuration

See File Transfer Configuration for path restrictions and glob patterns.

Network-Level Controls

Bind Address Restrictions

Limit which interfaces services listen on:

Bind Address	Access
127.0.0.1:1080	Localhost only
192.168.1.10:1080	Specific interface only
0.0.0.0:1080	All interfaces (use with caution)

Firewall Integration

Combine with host firewall rules:

# Only allow SOCKS5 from localhost
iptables -A INPUT -p tcp --dport 1080 -s 127.0.0.1 -j ACCEPT
iptables -A INPUT -p tcp --dport 1080 -j DROP

# Only allow mesh traffic from trusted peers
iptables -A INPUT -p udp --dport 4433 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p udp --dport 4433 -j DROP

mTLS as Access Control

With mTLS enabled, only agents with valid certificates can connect. This provides network-level access control before any authentication occurs.

Layered Security Example

Combine multiple controls for defense in depth:

# Layer 1: Network binding - internal interface only
socks5:
  address: "10.0.0.5:1080"
  # Layer 2: Authentication required
  auth:
    enabled: true
    users:
      - username: "internal-user"
        password_hash: "$2a$12$..."

# Layer 3: mTLS - only valid certificates accepted
tls:
  ca: "./certs/internal-ca.crt"
  cert: "./certs/agent.crt"
  key: "./certs/agent.key"
  mtls: true

listeners:
  - transport: quic
    address: "0.0.0.0:4433"

# Layer 4: Route restriction - internal networks only
exit:
  routes:
    - "10.0.0.0/8"

# Layer 5: Shell restriction - monitoring commands only
shell:
  enabled: true
  whitelist:
    - whoami
    - hostname
    - uptime
  password_hash: "$2a$12$..."

# Layer 6: File path restriction
file_transfer:
  enabled: true
  allowed_paths:
    - /tmp/transfers
  max_file_size: 10485760
  password_hash: "$2a$12$..."

This configuration requires bypassing six layers to cause damage.

Access Control Checklist

Minimum Security

• SOCKS5 bound to localhost or internal interface
• Shell disabled or empty whitelist
• File transfer disabled or empty allowed_paths

Recommended

• Authentication enabled on all services
• Exit routes limited to required networks
• Shell whitelist with only necessary commands
• File paths restricted to specific directories

High Security

• mTLS enabled for peer connections
• Per-user SOCKS5 accounts
• Strict shell whitelist (no shells, no cat)
• Firewall rules restricting access
• Debug logging for access monitoring

Troubleshooting

Route Not Found

Error: no route to host

Cause: Destination doesn't match any advertised exit route.

Solution: Check exit routes with curl http://localhost:8080/healthz | jq '.routes'

Command Rejected

Error: command not in whitelist

Cause: Command not in shell whitelist.

Solution: Add to whitelist or use an allowed command.

Path Not Allowed

Error: path not allowed

Cause: File path not in allowed_paths.

Solution: Use an allowed path or update configuration.

Next Steps

• Best Practices - Production hardening
• Authentication - Password security
• TLS/mTLS - Certificate-based access control