detecting-shadow-api-endpoints

# Detecting Shadow API Endpoints ## Overview Shadow APIs are API endpoints operating within an organization's environment that are not tracked, documented, or secured. They emerge from rapid development cycles, forgotten test environments, deprecated API versions left running, third-party integrations, or developer side projects deployed without governance. Shadow APIs bypass authentication and monitoring controls, creating hidden entry points for attackers. Studies show that up to 30% of API endpoints in large organizations are undocumented, making shadow API detection a critical component of API security posture management. ## When to Use - When investigating security incidents that require detecting shadow api endpoints - When building detection rules or threat hunting queries for this domain - When SOC analysts need structured procedures for this analysis type - When validating security monitoring coverage for related attack techniques ## Prerequisites - API gateway or reverse proxy with traffic logging (Kong, AWS API Gateway, Envoy) - Network traffic capture capability (packet broker, port mirroring) - Access to source code repositories and CI/CD pipeline configurations - Cloud provider access for configuration scanning (AWS, GCP, Azure) - API documentation inventory (OpenAPI specs, Swagger docs) - Python 3.8+ for custom discovery tooling ## Detection Methods ### 1. Traffic Analysis and Comparison Compare live API traffic against documented OpenAPI specifications to identify undocumented endpoints: ```python #!/usr/bin/env python3 """Shadow API Endpoint Detector Compares observed API traffic patterns against documented OpenAPI specifications to identify undocumented (shadow) endpoints. """ import json import re import yaml import sys from collections import defaultdict from datetime import datetime from typing import Dict, List, Set, Tuple, Optional from dataclasses import dataclass, field @dataclass class DiscoveredEndpoint: method: str path_pattern: str first_seen: str last_seen: str request_count: int source_ips: Set[str] = field(default_factory=set) status_codes: Set[int] = field(default_factory=set) has_auth_header: bool = False documented: bool = False class ShadowAPIDetector: # Common patterns for parameterized path segments PARAM_PATTERNS = [ (re.compile(r'/\d+'), '/{id}'), (re.compile(r'/[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}'), '/{uuid}'), (re.compile(r'/[a-zA-Z0-9]{20,40}'), '/{token}'), ] def __init__(self): self.documented_endpoints: Set[Tuple[str, str]] = set() self.discovered_endpoints: Dict[Tuple[str, str], DiscoveredEndpoint] = {} def load_openapi_spec(self, spec_path: str): """Load documented endpoints from OpenAPI specification.""" with open(spec_path, 'r') as f: if spec_path.endswith('.json'): spec = json.load(f) else: spec = yaml.safe_load(f) paths = spec.get('paths', {}) for path, methods in paths.items(): # Normalize OpenAPI path parameters normalized_path = re.sub(r'\{[^}]+\}', '{id}', path) for method in methods: if method.upper() in ('GET', 'POST', 'PUT', 'DELETE', 'PATCH', 'HEAD', 'OPTIONS'): self.documented_endpoints.add((method.upper(), normalized_path)) print(f"Loaded {len(self.documented_endpoints)} documented endpoints from {spec_path}") def normalize_path(self, path: str) -> str: """Normalize an observed path by replacing dynamic segments with placeholders.""" # Remove query string path = path.split('?')[0] for pattern, replacement in self.PARAM_PATTERNS: path = pattern.sub(replacement, path) return path def process_access_log(self, log_file: str, log_format: str = "common"): """Process API access logs to discover endpoints.""" patterns = { "common": re.compile( r'(?P<ip>[\d.]+)\s+\S+\s+\S+\s+\[(?P<time>[^\]]+)\]\s+' r'"(?P<method>\w+)\s+(?P<path>\S+)\s+\S+"\s+(?P<status>\d+)' ), "json": None # Handle JSON logs separately } with open(log_file, 'r') as f: for line in f: if log_format == "json": try: entry = json.loads(line) method = entry.get('method', entry.get('http_method', '')) path = entry.get('path', entry.get('uri', '')) status = int(entry.get('status', entry.get('status_code', 0))) ip = entry.get('remote_addr', entry.get('client_ip', '')) timestamp = entry.get('timestamp', entry.get('@timestamp', '')) has_auth = bool(entry.get('authorization', entry.get('auth_header', ''))) except json.JSONDecodeError: continue else: match = patterns[log_format].match(line) if not match: continue method = match.group('method') path = match.group('path') status = int(match.group('status')) ip = match.group('ip') timestamp = match.group('time') has_auth = 'Authorization' in line # Only process API paths if not path.startswith('/api') and not path.startswith('/v'): continue normalized = self.normalize_path(path) key = (method.upper(), normalized) if key not in self.discovered_endpoints: self.discovered_endpoints[key] = DiscoveredEndpoint( method=method.upper(), path_pattern=normalized, first_seen=timestamp, last_seen=timestamp, request_count=0, documented=(key in self.documented_endpoints) ) endpoint = self.discovered_endpoints[key] endpoint.request_count += 1 endpoint.last_seen = timestamp endpoint.source_ips.add(ip) endpoint.status_codes.add(status) if has_auth: endpoint.has_auth_header = True def identify_shadow_apis(self) -> List[DiscoveredEndpoint]: """Identify endpoints that are not in the documented specification.""" shadows = [] for key, endpoint in self.discovered_endpoints.items(): if not endpoint.documented: shadows.append(endpoint) # Sort by request count descending (most active shadows first) shadows.sort(key=lambda e: e.request_count, reverse=True) return shadows def classify_risk(self, endpoint: DiscoveredEndpoint) -> str: """Classify the risk level of a shadow endpoint.""" risk_score = 0 # No authentication observed if not endpoint.has_auth_header: risk_score += 3 # High traffic volume if endpoint.request_count > 1000: risk_score += 2 elif endpoint.request_count > 100: risk_score += 1 # Multiple source IPs (wider exposure) if len(endpoint.source_ips) > 10: risk_score += 2 # Successful responses (endpoint is functional) if 200 in endpoint.status_codes or 201 in endpoint.status_codes: risk_score += 1 # Write operations are higher risk if endpoint.method in ('POST', 'PUT', 'DELETE', 'PATCH'): risk_score += 2 # Sensitive path patterns sensitive_patterns = ['admin', 'internal', 'debug', 'test', 'backup', 'config', 'health', 'metrics', 'graphql', 'console'] for pattern in sensitive_patterns: if pattern in endpoint.path_pattern.lower(): risk_score += 3 break if risk_score >= 8: return "CRITICAL" elif risk_score >= 5: return "HIGH" elif risk_score >= 3: return "MEDIUM" return "LOW" def generate_report(self) -> dict: """Generate a comprehensive shadow API discovery report.""" shadows = self.identify_shadow_apis() total_documented = len(self.documented_endpoints) total_discovered = len(self.discovered_endpoints) report = { "scan_date": datetime.now().isoformat(), "summary": { "documented_endpoints": total_documented, "total_discovered_endpoints": total_discovered, "shadow_endpoints": len(shadows), "shadow_ratio": f"{len(shadows)/max(total_discovered,1)*100:.1f}%", }, "shadow_endpoints": [] } for endpoint in shadows: risk = self.classify_risk(endpoint) report["shadow_endpoints"].append({ "method": endpoint.method, "path": endpoint.path_pattern, "risk_level": risk, "request_count": endpoint.request_count, "unique_sources": len(endpoint.source_ips), "authenticated": endpoint.has_auth_header, "status_codes": sorted(endpoint.status_codes), "first_seen": endpoint.first_seen, "last_seen": endpoint.last_seen, }) return report def main(): detector = ShadowAPIDetector() # Load documented API specifications spec_files = sys.argv[1:] if len(sys.argv) > 1 else ["openapi.yaml"] for spec in spec_files: if spec.endswith(('.yaml', '.yml', '.json')): detector.load_openapi_spec(spec) # Process access logs detector.process_access_log("/var/log/api/access.log") report = detector.generate_report() print(f"\n{'='*60}") print(f"SHADOW API DISCOVERY REPORT") print(f"{'='*60}") print(f"Documented: {report['summary']['documented_endpoints']}") print(f"Discovered: {report['summary']['total_discovered_endpoints']}") print(f"Shadow: {report['summary']['shadow_endpoints']} ({report['summary']['shadow_ratio']})") print() for ep in report["shadow_endpoints"]: risk_marker = {"CRITICAL": "[!!!]", "HIGH": "[!!]", "MEDIUM": "[!]", "LOW": "[.]"} print(f" {risk_marker.get(ep['risk_level'], '[?]')} {ep['method']} {ep['path']}") print(f" Risk: {ep['risk_level']} | Requests: {ep['request_count']} | Auth: {ep['authenticated']}") # Save full report with open("shadow_api_report.json", "w") as f: json.dump(report, f, indent=2, default=str) print(f"\nFull report saved to shadow_api_report.json") if __name__ == "__main__": main() ``` ### 2. Cloud Configuration Scanning ```bash # AWS: Discover API Gateway endpoints not in documentation aws apigateway get-rest-apis --query 'items[*].[name,id]' --output table # List all routes for each API aws apigatewayv2 get-apis --query 'Items[*].[Name,ApiId,ProtocolType]' --output table # AWS Lambda function URLs (potential shadow APIs) aws lambda list-function-url-configs --function-name "*" 2>/dev/null # Find ALB listener rules routing to undocumented backends aws elbv2 describe-rules --listener-arn $LISTENER_ARN \ --query 'Rules[*].[Priority,Conditions[0].Values[0],Actions[0].TargetGroupArn]' ``` ### 3. Source Code Repository Mining ```bash # Search for undocumented route definitions in source code # Express.js routes grep -rn "app\.\(get\|post\|put\|delete\|patch\)" --include="*.js" --include="*.ts" src/ # Flask/Django routes grep -rn "@app\.route\|@api\.route\|path(" --include="*.py" src/ # Spring Boot endpoints grep -rn "@\(Get\|Post\|Put\|Delete\|Patch\)Mapping\|@RequestMapping" --include="*.java" src/ # Compare found routes against OpenAPI specification diff <(grep -roh "'/api/[^']*'" src/ | sort -u) \ <(yq '.paths | keys[]' openapi.yaml | sort -u) ``` ## Prevention and Governance ### API Registration Gateway Policy ```yaml # Kong plugin configuration - reject unregistered routes plugins: - name: request-validator config: allowed_content_types: - application/json body_schema: null