Update README with comprehensive Phase 1 documentation
Documents all new features: - Extension enumeration detection with config examples - SIP message validation rules and modes - Topology hiding (B2BUA-lite) with request/response flow diagrams - Complete Caddyfile configuration reference - Prometheus metrics reference - Admin API endpoints - Integration examples for FreePBX, Kamailio, and HA setups - Security considerations Architecture diagram updated to show full processing pipeline.
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README.md
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README.md
@ -1,15 +1,41 @@
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# Caddy SIP Guardian
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A custom Caddy module that provides SIP-aware rate limiting, IP banning, and attack detection at Layer 4.
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A comprehensive Caddy module providing SIP-aware security at Layer 4. Protects your VoIP infrastructure with intelligent rate limiting, attack detection, message validation, and topology hiding.
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## Features
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### Core Protection
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- **Layer 4 SIP Proxying**: Handle SIP traffic (UDP/TCP/TLS) before it reaches your PBX
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- **Intelligent Rate Limiting**: Track failed attempts per IP with configurable windows
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- **Intelligent Rate Limiting**: Per-method token bucket rate limiting with burst support
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- **Automatic Banning**: Ban IPs that exceed failure thresholds
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- **Attack Detection**: Detect common SIP scanning tools (sipvicious, friendly-scanner, etc.)
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- **Attack Detection**: Detect common SIP scanning tools (SIPVicious, friendly-scanner, etc.)
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- **CIDR Whitelisting**: Whitelist trusted networks
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- **Admin API**: RESTful API for managing bans and viewing stats
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- **GeoIP Blocking**: Block traffic by country using MaxMind databases
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### Extension Enumeration Detection
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- **Count-based Detection**: Block IPs probing too many unique extensions
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- **Sequential Pattern Detection**: Detect numeric extension scanning (100, 101, 102...)
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- **Rapid-fire Detection**: Catch high-speed enumeration attempts
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- **Configurable Exemptions**: Whitelist common extensions like voicemail
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### SIP Message Validation
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- **RFC 3261 Compliance**: Enforce required headers and message structure
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- **Injection Prevention**: Block NULL bytes and binary injection attacks
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- **Content-Length Validation**: Detect body/header mismatches
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- **Multiple Modes**: Permissive, strict, or paranoid validation
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### Topology Hiding (B2BUA-lite)
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- **Via Header Rewriting**: Hide internal proxy chain
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- **Contact Header Rewriting**: Mask internal IP addresses
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- **Sensitive Header Stripping**: Remove P-Asserted-Identity, Server, etc.
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- **Call-ID Anonymization**: Prevent dialog correlation attacks
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- **Private IP Masking**: Automatically hide RFC 1918 addresses
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### Observability
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- **Prometheus Metrics**: Comprehensive metrics for monitoring
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- **Webhook Notifications**: Real-time alerts for security events
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- **SQLite Persistence**: Durable ban storage across restarts
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- **Admin API**: RESTful API for management and stats
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## Architecture
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@ -17,27 +43,26 @@ A custom Caddy module that provides SIP-aware rate limiting, IP banning, and att
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Internet
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│
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▼
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┌─────────────────────────────────────┐
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│ Caddy SIP Guardian (Layer 4) │
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│ ┌─────────────────────────────────┐│
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│ │ SIP Matcher ││
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│ │ - Detects SIP methods ││
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│ │ - Matches REGISTER, INVITE, etc ││
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│ └─────────────────────────────────┘│
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│ ┌─────────────────────────────────┐│
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│ │ SIP Handler ││
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│ │ - Check banned IPs ││
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│ │ - Check whitelists ││
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│ │ - Detect attack patterns ││
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│ │ - Record failures ││
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│ └─────────────────────────────────┘│
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└─────────────────────────────────────┘
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┌─────────────────────────────────────────────────────────────┐
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│ Caddy SIP Guardian (Layer 4) │
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│ ┌─────────────────────────────────────────────────────────┐│
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│ │ 1. SIP Matcher - Identifies SIP traffic ││
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│ │ 2. Ban Check - Reject banned IPs ││
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│ │ 3. Whitelist Check - Skip checks for trusted IPs ││
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│ │ 4. GeoIP Check - Block by country ││
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│ │ 5. Validation - RFC 3261 compliance ││
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│ │ 6. Pattern Detection - Scanner fingerprinting ││
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│ │ 7. Enumeration Check - Extension scanning detection ││
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│ │ 8. Rate Limiting - Per-method token buckets ││
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│ │ 9. Topology Hiding - Header rewriting (optional) ││
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│ └─────────────────────────────────────────────────────────┘│
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└─────────────────────────────────────────────────────────────┘
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│
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▼
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┌─────────────────────────────────────┐
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│ FreePBX / Asterisk │
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│ (Protected from scanners) │
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└─────────────────────────────────────┘
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┌─────────────────────────────────────────────────────────────┐
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│ FreePBX / Asterisk / Kamailio │
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│ (Protected from scanners, enumeration, and topology leaks) │
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└─────────────────────────────────────────────────────────────┘
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```
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## Quick Start
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@ -51,32 +76,252 @@ make run
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# View logs
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make logs
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# Run tests
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make test
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```
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## Configuration
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### Complete Caddyfile Example
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```caddyfile
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{
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layer4 {
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# UDP SIP (standard port)
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udp/:5060 {
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@sip sip {
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methods REGISTER INVITE OPTIONS ACK BYE CANCEL INFO NOTIFY SUBSCRIBE MESSAGE
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}
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route @sip {
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sip_guardian {
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# Core settings
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max_failures 5
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find_time 10m
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ban_time 1h
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whitelist 10.0.0.0/8 192.168.0.0/16
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# GeoIP blocking (optional)
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geoip_db /etc/caddy/GeoLite2-Country.mmdb
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blocked_countries CN RU
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# Per-method rate limiting
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rate_limit {
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register 10/s burst 20
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invite 5/s burst 10
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options 20/s burst 50
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}
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# Extension enumeration detection
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enumeration {
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max_extensions 20
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extension_window 5m
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sequential_threshold 5
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rapid_fire_count 10
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rapid_fire_window 30s
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ban_time 2h
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exempt_extensions 100 200 9999
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}
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# SIP message validation
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validation {
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enabled true
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mode strict
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max_message_size 65535
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ban_on_null_bytes true
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ban_on_binary_injection true
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}
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# Prometheus metrics
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metrics {
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enabled true
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}
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# Webhook notifications
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webhooks {
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url https://hooks.example.com/sip-alerts
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events ban unban attack enumeration
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}
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# SQLite persistence
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storage {
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path /var/lib/caddy/sip_guardian.db
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}
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}
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# Optional: Topology hiding
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sip_topology_hider {
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proxy_host 203.0.113.1
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proxy_port 5060
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upstream udp/192.168.1.100:5060
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rewrite_via
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rewrite_contact
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strip_headers P-Preferred-Identity P-Asserted-Identity Server User-Agent
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hide_private_ips
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# anonymize_call_id # Optional: randomize Call-IDs
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}
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proxy udp/freepbx:5060
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}
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}
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# TCP SIP
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tcp/:5060 {
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@sip sip
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route @sip {
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sip_guardian { ... }
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proxy tcp/freepbx:5060
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}
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}
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# SIP over TLS
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tcp/:5061 {
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@sip tls sni sip.example.com
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route @sip {
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sip_guardian { ... }
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tls
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proxy tcp/freepbx:5060
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}
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}
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}
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}
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# Admin API
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:2020 {
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handle /api/sip-guardian/* {
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sip_guardian_admin
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}
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# Prometheus metrics endpoint
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handle /metrics {
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metrics
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}
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}
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```
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### Environment Variables
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| Variable | Default | Description |
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|----------|---------|-------------|
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| `SIP_UPSTREAM_HOST` | `freepbx` | Upstream SIP server hostname |
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| `SIP_UPSTREAM_PORT` | `5060` | Upstream SIP port |
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| `SIP_UPSTREAM_TLS_PORT` | `5061` | Upstream SIP TLS port |
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| `SIP_GUARDIAN_MAX_FAILURES` | `5` | Failures before ban |
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| `SIP_GUARDIAN_FIND_TIME` | `10m` | Time window for counting failures |
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| `SIP_GUARDIAN_BAN_TIME` | `1h` | Ban duration |
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### Caddyfile Directives
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## Feature Details
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### Extension Enumeration Detection
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Protects against tools like SIPVicious `svwar` that scan for valid extensions:
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```caddyfile
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sip_guardian {
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max_failures 5 # Ban after 5 failures
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find_time 10m # Within 10 minute window
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ban_time 1h # Ban for 1 hour
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whitelist 10.0.0.0/8 192.168.0.0/16
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enumeration {
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max_extensions 20 # Ban after 20 unique extensions probed
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extension_window 5m # Within this time window
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sequential_threshold 5 # Ban if 5+ consecutive extensions (100,101,102...)
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rapid_fire_count 10 # Ban if 10+ extensions in rapid_fire_window
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rapid_fire_window 30s
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ban_time 2h # Enumeration bans last longer
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exempt_extensions 100 200 9999 # Don't count these (voicemail, etc.)
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}
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```
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**Detection Methods:**
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1. **Count Threshold**: Too many unique extensions from one IP
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2. **Sequential Pattern**: Consecutive numeric extensions indicate scanning
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3. **Rapid Fire**: High-speed probing is clearly automated
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### SIP Message Validation
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Enforces RFC 3261 compliance and blocks malformed/malicious packets:
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```caddyfile
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validation {
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enabled true
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mode strict # permissive, strict, or paranoid
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max_message_size 65535 # Reject oversized messages
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ban_on_null_bytes true # Immediate ban for NULL byte injection
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ban_on_binary_injection true
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disabled_rules via_invalid_branch # Skip specific rules
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}
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```
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**Validation Modes:**
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- **Permissive**: Log violations, only block critical attacks
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- **Strict**: Enforce RFC 3261 required headers
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- **Paranoid**: Additional heuristics for edge cases
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**Validation Rules:**
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| Rule | Severity | Action |
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|------|----------|--------|
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| `null_bytes` | CRITICAL | Immediate ban |
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| `binary_injection` | CRITICAL | Immediate ban |
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| `missing_via` | HIGH | Count toward ban |
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| `missing_from` | HIGH | Count toward ban |
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| `missing_to` | HIGH | Count toward ban |
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| `missing_call_id` | HIGH | Count toward ban |
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| `missing_cseq` | HIGH | Count toward ban |
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| `content_length_mismatch` | HIGH | Count toward ban |
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| `oversized_message` | HIGH | Count toward ban |
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| `invalid_request_uri` | MEDIUM | Reject only |
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### Topology Hiding
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Hide your internal infrastructure from external attackers:
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```caddyfile
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sip_topology_hider {
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# Your public-facing address
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proxy_host 203.0.113.1
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proxy_port 5060
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# Internal PBX (never exposed)
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upstream udp/192.168.1.100:5060
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# Enable Via header insertion
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rewrite_via
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# Replace internal Contact URIs with proxy address
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rewrite_contact
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# Remove headers that leak internal info
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strip_headers P-Preferred-Identity P-Asserted-Identity Remote-Party-ID Server User-Agent X-Asterisk-HangupCause
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# Replace RFC 1918 addresses in all headers
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hide_private_ips
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# Optional: Randomize Call-IDs (prevents dialog correlation)
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# anonymize_call_id
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}
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```
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**What It Hides:**
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- Internal IP addresses (192.168.x.x, 10.x.x.x, 172.16-31.x.x)
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- Via header chain revealing internal proxies
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- Contact URIs pointing to internal hosts
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- Server/User-Agent revealing software versions
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- P-Asserted-Identity revealing internal extensions
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**Request Flow:**
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```
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External UA → Caddy → Asterisk
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│
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└─ Adds Via: SIP/2.0/UDP proxy.example.com;branch=z9hG4bK...
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└─ Rewrites Contact: <sip:proxy.example.com:5060>
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└─ Strips: Server, P-Asserted-Identity
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```
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**Response Flow:**
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```
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Asterisk → Caddy → External UA
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│
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└─ Removes top Via (proxy's)
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└─ Dialog state routes response correctly
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```
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## Admin API
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### List Banned IPs
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@ -89,11 +334,23 @@ curl http://localhost:2020/api/sip-guardian/bans
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curl http://localhost:2020/api/sip-guardian/stats
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```
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Response:
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```json
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{
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"total_requests": 15234,
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"blocked_requests": 423,
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"active_bans": 12,
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"enumeration_detections": 5,
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"validation_failures": 89,
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"rate_limited": 156
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}
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```
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### Manually Ban IP
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```bash
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curl -X POST http://localhost:2020/api/sip-guardian/ban/192.168.1.100 \
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-H "Content-Type: application/json" \
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-d '{"reason": "manual_ban"}'
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-d '{"reason": "manual_ban", "duration": "24h"}'
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```
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### Unban IP
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@ -101,15 +358,51 @@ curl -X POST http://localhost:2020/api/sip-guardian/ban/192.168.1.100 \
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curl -X DELETE http://localhost:2020/api/sip-guardian/unban/192.168.1.100
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```
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### View Enumeration Stats
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```bash
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curl http://localhost:2020/api/sip-guardian/enumeration/stats
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```
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### View Validation Stats
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```bash
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curl http://localhost:2020/api/sip-guardian/validation/stats
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```
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## Prometheus Metrics
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```
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# Core metrics
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sip_guardian_requests_total{method="REGISTER"}
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sip_guardian_blocked_total{reason="banned"}
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sip_guardian_active_bans
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# Rate limiting
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sip_guardian_rate_limited_total{method="INVITE"}
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# Enumeration detection
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sip_guardian_enumeration_detections_total{reason="sequential_pattern"}
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sip_guardian_enumeration_tracked_ips
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# Validation
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sip_guardian_validation_violations_total{rule="missing_via"}
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sip_guardian_validation_results_total{result="valid"}
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sip_guardian_message_size_bytes
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# GeoIP
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sip_guardian_geoip_blocked_total{country="CN"}
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```
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## Detected Attack Patterns
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The module automatically detects and flags:
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- **sipvicious** - Popular SIP scanning tool
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- **friendly-scanner** - Another common scanner
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- **sipcli** - SIP command line tool
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- **sip-scan** - Generic SIP scanners
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- Common test extensions (100, 1000)
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- **SIPVicious** (`sipvicious`, `friendly-scanner`)
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- **SIPScan** (`sip-scan`, `sipcli`)
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- **Asterisk scanners** (`Asterisk PBX`)
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- **Common test extensions** (100, 1000, 9999)
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- **Sequential extension probing**
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- **NULL byte injection**
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- **Binary payload injection**
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## Building from Source
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@ -117,19 +410,116 @@ The module automatically detects and flags:
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# Using xcaddy
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xcaddy build \
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--with github.com/mholt/caddy-l4 \
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--with github.com/mholt/caddy-ratelimit \
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--with github.com/ryanmalloy/caddy-sip-guardian
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--with git.supported.systems/rsp2k/caddy-sip-guardian
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# Or with local development
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xcaddy build \
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--with github.com/mholt/caddy-l4 \
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--with git.supported.systems/rsp2k/caddy-sip-guardian=/path/to/local/module
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```
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## Integration with FreePBX
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## Testing
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This module is designed to sit in front of FreePBX/Asterisk:
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```bash
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# Run all unit tests
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make test
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1. All SIP traffic hits Caddy first
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2. Malicious traffic is blocked at the edge
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3. Only legitimate traffic reaches your PBX
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4. FreePBX doesn't need its own fail2ban for SIP
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# Test enumeration detection
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make test-enumeration
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# Test validation
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make test-validation
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# Test with SIPVicious (in sandbox)
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make sandbox-up
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make test-scanner
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```
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## Integration Examples
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### With FreePBX/Asterisk
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```caddyfile
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{
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layer4 {
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udp/:5060 {
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@sip sip
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route @sip {
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sip_guardian {
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max_failures 3
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ban_time 24h
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whitelist 10.0.0.0/8
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}
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proxy udp/freepbx:5060
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}
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||||
}
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||||
}
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||||
}
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```
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|
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### With Kamailio (as SBC)
|
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```caddyfile
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{
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layer4 {
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udp/:5060 {
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@sip sip
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route @sip {
|
||||
sip_guardian { ... }
|
||||
sip_topology_hider {
|
||||
proxy_host sbc.example.com
|
||||
proxy_port 5060
|
||||
upstream udp/kamailio:5060
|
||||
rewrite_via
|
||||
rewrite_contact
|
||||
}
|
||||
proxy udp/kamailio:5060
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
### High Availability Setup
|
||||
```caddyfile
|
||||
{
|
||||
layer4 {
|
||||
udp/:5060 {
|
||||
@sip sip
|
||||
route @sip {
|
||||
sip_guardian {
|
||||
storage {
|
||||
# Shared storage for HA
|
||||
path /shared/sip_guardian.db
|
||||
}
|
||||
}
|
||||
# Load balance across PBX cluster
|
||||
proxy udp/pbx1:5060 udp/pbx2:5060 udp/pbx3:5060 {
|
||||
lb_policy round_robin
|
||||
health_check interval=30s
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
## Security Considerations
|
||||
|
||||
1. **Whitelist Internal Networks**: Always whitelist your internal networks to prevent self-blocking
|
||||
2. **Start Permissive**: Begin with permissive validation mode and tighten after monitoring
|
||||
3. **Monitor False Positives**: Watch metrics for legitimate traffic being blocked
|
||||
4. **Regular Updates**: Keep GeoIP databases current
|
||||
5. **Webhook Alerts**: Configure webhooks for immediate security event notification
|
||||
|
||||
## License
|
||||
|
||||
MIT
|
||||
|
||||
## Contributing
|
||||
|
||||
Contributions welcome! Please see CONTRIBUTING.md for guidelines.
|
||||
|
||||
## Related Projects
|
||||
|
||||
- [caddy-l4](https://github.com/mholt/caddy-l4) - Layer 4 proxy for Caddy
|
||||
- [Caddy](https://caddyserver.com/) - The HTTP/2 web server with automatic HTTPS
|
||||
- [SIPVicious](https://github.com/EnableSecurity/sipvicious) - SIP security testing tools
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user