detecting-shadow-api-endpoints

name	detecting-shadow-api-endpoints
description	Discover and inventory shadow API endpoints that operate outside documented OpenAPI/Swagger specs, using traffic analysis against API gateways (Kong, AWS API Gateway, Envoy), cloud configuration scanning, and source code repository mining for undocumented routes. Use when assessing API attack surface, auditing for forgotten test environments or deprecated API versions still running, or building an API registration governance policy.
domain	cybersecurity
subdomain	api-security
tags	["api-security","shadow-apis","api-discovery","undocumented-apis","zombie-apis","api-inventory","attack-surface-management","api-governance"]
version	1.0
author	mahipal
license	Apache-2.0
nist_csf	["PR.PS-01","ID.RA-01","PR.DS-10","DE.CM-01"]
mitre_attack	["T1190","T1133","T1526","T1213"]

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:

#!/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


 :
    method: 
    path_pattern: 
    first_seen: 
    last_seen: 
    request_count: 
    source_ips: [] = field(default_factory=)
    status_codes: [] = field(default_factory=)
    has_auth_header:  = 
    documented:  = 

 :
    
    PARAM_PATTERNS = [
        (re.(), ),
        (re.(), ),
        (re.(), ),
    ]

     ():
        .documented_endpoints: [[, ]] = ()
        .discovered_endpoints: [[, ], DiscoveredEndpoint] = {}

     ():
        
         (spec_path, )  f:
             spec_path.endswith():
                spec = json.load(f)
            :
                spec = yaml.safe_load(f)

        paths = spec.get(, {})
         path, methods  paths.items():
            
            normalized_path = re.sub(, , path)
             method  methods:
                 method.upper()  (, , , , , , ):
                    .documented_endpoints.add((method.upper(), normalized_path))

        ()

     () -> :
        
        
        path = path.split()[]

         pattern, replacement  .PARAM_PATTERNS:
            path = pattern.sub(replacement, path)

         path

     ():
        
        patterns = {
            : re.(
                
                
            ),
            :   
        }

         (log_file, )  f:
             line  f:
                 log_format == :
                    :
                        entry = json.loads(line)
                        method = entry.get(, entry.get(, ))
                        path = entry.get(, entry.get(, ))
                        status = (entry.get(, entry.get(, )))
                        ip = entry.get(, entry.get(, ))
                        timestamp = entry.get(, entry.get(, ))
                        has_auth = (entry.get(, entry.get(, )))
                     json.JSONDecodeError:
                        
                :
                     = patterns[log_format].(line)
                      :
                        
                    method = .group()
                    path = .group()
                    status = (.group())
                    ip = .group()
                    timestamp = .group()
                    has_auth =   line

                
                  path.startswith()   path.startswith():
                    

                normalized = .normalize_path(path)
                key = (method.upper(), normalized)

                 key   .discovered_endpoints:
                    .discovered_endpoints[key] = DiscoveredEndpoint(
                        method=method.upper(),
                        path_pattern=normalized,
                        first_seen=timestamp,
                        last_seen=timestamp,
                        request_count=,
                        documented=(key  .documented_endpoints)
                    )

                endpoint = .discovered_endpoints[key]
                endpoint.request_count += 
                endpoint.last_seen = timestamp
                endpoint.source_ips.add(ip)
                endpoint.status_codes.add(status)
                 has_auth:
                    endpoint.has_auth_header = 

     () -> [DiscoveredEndpoint]:
        
        shadows = []
         key, endpoint  .discovered_endpoints.items():
              endpoint.documented:
                shadows.append(endpoint)

        
        shadows.sort(key= e: e.request_count, reverse=)
         shadows

     () -> :
        
        risk_score = 

        
          endpoint.has_auth_header:
            risk_score += 

        
         endpoint.request_count > :
            risk_score += 
         endpoint.request_count > :
            risk_score += 

        
         (endpoint.source_ips) > :
            risk_score += 

        
           endpoint.status_codes    endpoint.status_codes:
            risk_score += 

        
         endpoint.method  (, , , ):
            risk_score += 

        
        sensitive_patterns = [, , , , ,
                            , , , , ]
         pattern  sensitive_patterns:
             pattern  endpoint.path_pattern.lower():
                risk_score += 
                

         risk_score >= :
             
         risk_score >= :
             
         risk_score >= :
             
         

     () -> :
        
        shadows = .identify_shadow_apis()
        total_documented = (.documented_endpoints)
        total_discovered = (.discovered_endpoints)

        report = {
            : datetime.now().isoformat(),
            : {
                : total_documented,
                : total_discovered,
                : (shadows),
                : ,
            },
            : []
        }

         endpoint  shadows:
            risk = .classify_risk(endpoint)
            report[].append({
                : endpoint.method,
                : endpoint.path_pattern,
                : risk,
                : endpoint.request_count,
                : (endpoint.source_ips),
                : endpoint.has_auth_header,
                : (endpoint.status_codes),
                : endpoint.first_seen,
                : endpoint.last_seen,
            })

         report


 ():
    detector = ShadowAPIDetector()

    
    spec_files = sys.argv[:]  (sys.argv) >   []
     spec  spec_files:
         spec.endswith((, , )):
            detector.load_openapi_spec(spec)

    
    detector.process_access_log()

    report = detector.generate_report()

    ()
    ()
    ()
    ()
    ()
    ()
    ()

     ep  report[]:
        risk_marker = {: , : , : , : }
        ()
        ()

    
     (, )  f:
        json.dump(report, f, indent=, default=)
    ()


 __name__ == :
    main()