Skill v1.0.1
currentAutomated scan100/1003 files
version: "1.0.1" name: trivy-offline-vulnerability-scanning description: Use Trivy vulnerability scanner in offline mode to discover security vulnerabilities in dependency files. This skill covers setting up offline scanning, executing Trivy against package lock files, and generating JSON vulnerability reports without requiring internet access.
Trivy Offline Vulnerability Scanning
This skill provides guidance on using Trivy, an open-source security scanner, to discover vulnerabilities in software dependencies using offline mode.
Overview
Trivy is a comprehensive vulnerability scanner that can analyze various targets including container images, filesystems, and dependency lock files. Offline scanning is crucial for:
- Air-gapped environments without internet access
- Reproducible security audits with fixed vulnerability databases
- Faster CI/CD pipelines avoiding network latency
- Compliance requirements for controlled environments
Why Offline Mode?
Challenges with Online Scanning
- Network dependency introduces failure points
- Database updates can cause inconsistent results across runs
- Slower execution due to download times
- Security policies may restrict external connections
Benefits of Offline Scanning
- Reproducibility: Same database = same results
- Speed: No network overhead
- Reliability: No external dependencies
- Compliance: Works in restricted environments
Trivy Database Structure
Trivy's vulnerability database consists of:
- trivy.db: SQLite database containing CVE information
- metadata.json: Database version and update timestamp
Database location: <cache-dir>/db/trivy.db
Offline Scanning Workflow
Step 1: Verify Database Existence
Before scanning, ensure the offline database is available:
import osimport sysTRIVY_CACHE_PATH = './trivy-cache'# Check for database filedb_path = os.path.join(TRIVY_CACHE_PATH, "db", "trivy.db")if not os.path.exists(db_path):print(f"[!] Error: Trivy database not found at {db_path}")print(" Download database first with:")print(f" trivy image --download-db-only --cache-dir {TRIVY_CACHE_PATH}")sys.exit(1)
Step 2: Construct Trivy Command
Key flags for offline scanning:
| Flag | Purpose | |
|---|---|---|
fs <target> | Scan filesystem/file (e.g., package-lock.json) | |
--format json | Output in JSON format for parsing | |
--output <file> | Save results to file | |
--scanners vuln | Scan only for vulnerabilities (not misconfigs) | |
--skip-db-update | Critical: Do not update database | |
--offline-scan | Enable offline mode | |
--cache-dir <path> | Path to pre-downloaded database |
import subprocessTARGET_FILE = 'package-lock.json'OUTPUT_FILE = 'trivy_report.json'TRIVY_CACHE_PATH = './trivy-cache'command = ["trivy", "fs", TARGET_FILE,"--format", "json","--output", OUTPUT_FILE,"--scanners", "vuln","--skip-db-update", # Prevent online updates"--offline-scan", # Enable offline mode"--cache-dir", TRIVY_CACHE_PATH]
Step 3: Execute Scan
try:result = subprocess.run(command,capture_output=True,text=True,check=False # Don't raise exception on non-zero exit)if result.returncode != 0:print("[!] Trivy scan failed:")print(result.stderr)sys.exit(1)print("[*] Scan completed successfully")print(f"[*] Results saved to: {OUTPUT_FILE}")except FileNotFoundError:print("[!] Error: 'trivy' command not found")print(" Install Trivy: https://aquasecurity.github.io/trivy/latest/getting-started/installation/")sys.exit(1)
Complete Example
import osimport sysimport subprocessdef run_trivy_offline_scan(target_file, output_file, cache_dir='./trivy-cache'):"""Execute Trivy vulnerability scan in offline mode.Args:target_file: Path to file to scan (e.g., package-lock.json)output_file: Path to save JSON resultscache_dir: Path to Trivy offline database"""print(f"[*] Starting Trivy offline scan...")print(f" Target: {target_file}")print(f" Database: {cache_dir}")# Verify database existsdb_path = os.path.join(cache_dir, "db", "trivy.db")if not os.path.exists(db_path):print(f"[!] Error: Database not found at {db_path}")sys.exit(1)# Build commandcommand = ["trivy", "fs", target_file,"--format", "json","--output", output_file,"--scanners", "vuln","--skip-db-update","--offline-scan","--cache-dir", cache_dir]# Executetry:result = subprocess.run(command, capture_output=True, text=True)if result.returncode != 0:print("[!] Scan failed:")print(result.stderr)sys.exit(1)print("[*] Scan completed successfully")return output_fileexcept FileNotFoundError:print("[!] Trivy not found. Install from:")print(" https://aquasecurity.github.io/trivy/")sys.exit(1)# Usageif __name__ == "__main__":run_trivy_offline_scan(target_file='package-lock.json',output_file='trivy_report.json')
JSON Output Structure
Trivy outputs vulnerability data in this format:
{"Results": [{"Target": "package-lock.json","Vulnerabilities": [{"VulnerabilityID": "CVE-2021-44906","PkgName": "minimist","InstalledVersion": "1.2.5","FixedVersion": "1.2.6","Severity": "CRITICAL","Title": "Prototype Pollution in minimist","PrimaryURL": "https://avd.aquasec.com/nvd/cve-2021-44906","CVSS": {"nvd": { "V3Score": 9.8 }}}]}]}
Common Issues
Issue: "failed to initialize DB"
Cause: Database not found or corrupted Solution: Re-download database or check --cache-dir path
Issue: Scan finds no vulnerabilities when they exist
Cause: Database is outdated Solution: Download newer database (before going offline)
Issue: "command not found: trivy"
Cause: Trivy not installed or not in PATH Solution: Install Trivy following official documentation
Dependencies
Required Tools
- Trivy: Version 0.40.0 or later recommended
``bash # Installation (example for Debian/Ubuntu) wget -qO - https://aquasecurity.github.io/trivy-repo/deb/public.key | apt-key add - echo "deb https://aquasecurity.github.io/trivy-repo/deb $(lsb_release -sc) main" | tee -a /etc/apt/sources.list.d/trivy.list apt-get update apt-get install trivy ``
Python Modules
subprocess(standard library)os(standard library)sys(standard library)