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Detect and prevent API enumeration attacks including BOLA and IDOR exploitation by monitoring sequential identifier access patterns and authorization failures.
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SOC 職業分類に基づく
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Tests APIs for Broken Function Level Authorization (BFLA) vulnerabilities where regular users can invoke administrative functions or access privileged API endpoints by directly calling them. The tester identifies admin and privileged endpoints, then attempts to access them with regular user credentials by manipulating HTTP methods, URL paths, and request parameters. Maps to OWASP API5:2023 Broken Function Level Authorization. Activates for requests involving BFLA testing, admin endpoint bypass, function-level access control testing, or API privilege escalation.
Tests APIs for excessive data exposure where endpoints return more data than the client application needs, relying on the frontend to filter sensitive fields. The tester intercepts API responses and analyzes them for leaked PII, internal identifiers, debug information, or sensitive business data that the UI does not display but the API transmits. This maps to OWASP API3:2023 Broken Object Property Level Authorization. Activates for requests involving API data leakage testing, excessive data exposure, response filtering bypass, or API over-fetching.
Exploits JWT algorithm confusion vulnerabilities where the server's token verification library accepts the algorithm specified in the JWT header rather than enforcing a fixed algorithm. The tester manipulates the alg header to switch from RS256 to HS256 (using the RSA public key as the HMAC secret), sets alg to none to bypass signature verification, or exploits kid/jku/x5u header injection to supply attacker-controlled keys. Activates for requests involving JWT algorithm confusion, alg none attack, key confusion attack, or JWT signature bypass.
Identifies and exploits SQL injection vulnerabilities in web applications during authorized penetration tests using manual techniques and automated tools like sqlmap. The tester detects injection points through error-based, union-based, blind boolean, and time-based blind techniques across all major database engines (MySQL, PostgreSQL, MSSQL, Oracle) to demonstrate data extraction, authentication bypass, and potential remote code execution. Activates for requests involving SQL injection testing, SQLi exploitation, database security assessment, or injection vulnerability verification.
| name | detecting-api-enumeration-attacks |
| description | Detect and prevent API enumeration attacks including BOLA and IDOR exploitation by monitoring sequential identifier access patterns and authorization failures. |
| domain | cybersecurity |
| subdomain | api-security |
| tags | ["api-security","enumeration","bola","idor","broken-object-level-authorization","owasp-api-top-10","access-control","rate-limiting"] |
| 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 | ["T1595","T1595.002","T1046","T1190","T1087"] |
API enumeration attacks occur when attackers systematically probe API endpoints with sequential or predictable identifiers to discover and access unauthorized resources. Broken Object Level Authorization (BOLA), ranked as API1:2023 in the OWASP API Security Top 10, is the most critical API vulnerability. Attackers manipulate object identifiers (user IDs, order numbers, account references) in API requests to bypass authorization and access other users' data. Detection requires monitoring for patterns of rapid sequential access attempts, authorization failures, and abnormal API usage behavior.
Attackers iterate through numeric or predictable identifiers:
GET /api/v1/users/1001 -> 200 OK
GET /api/v1/users/1002 -> 200 OK
GET /api/v1/users/1003 -> 403 Forbidden
GET /api/v1/users/1004 -> 200 OK
GET /api/v1/users/1005 -> 200 OK
...
Detection Indicators:
Even non-sequential identifiers can be enumerated if leaked through other endpoints:
# Attacker first harvests UUIDs from a list endpoint
GET /api/v1/posts?page=1 -> Returns post objects with author UUIDs
# Then uses those UUIDs to access restricted user data
GET /api/v1/users/a3f2c1e4-... -> Private user profile
GET /api/v1/users/b7d9e8f1-... -> Private user profile
# Authenticated as user_id=100, attempting to access other users' orders
GET /api/v1/orders?user_id=101
GET /api/v1/orders?user_id=102
GET /api/v1/orders?user_id=103
# Detect sequential ID enumeration on API endpoints
index=api_logs sourcetype=api_access
| rex field=uri_path "(?<endpoint>/api/v\d+/\w+/)(?<object_id>\d+)"
| stats count as request_count,
dc(object_id) as unique_ids,
values(status_code) as status_codes,
min(_time) as first_seen,
max(_time) as last_seen
by src_ip, endpoint, user_session
| eval time_span = last_seen - first_seen
| eval requests_per_second = request_count / max(time_span, 1)
| where unique_ids > 20 AND requests_per_second > 2
| eval severity = case(
unique_ids > 100, "critical",
unique_ids > 50, "high",
unique_ids > 20, "medium",
1==1, "low"
)
| sort - unique_ids
| table src_ip, endpoint, unique_ids, request_count, requests_per_second,
status_codes, severity
# Detect BOLA via authorization failure patterns
index=api_logs sourcetype=api_access status_code IN (401, 403)
| bin _time span=5m
| stats count as failure_count,
dc(uri_path) as unique_paths,
values(uri_path) as attempted_paths
by _time, src_ip, user_id
| where failure_count > 10
| eval attack_type = if(unique_paths > 5, "enumeration", "brute_force")
{
"rule": {
"name": "API Object Enumeration Detection",
"description": "Detects rapid sequential access to API objects with mixed authorization results",
"type": "threshold",
"index": ["api-access-*"],
"query": {
"bool": {
"must": [
{ "regexp": { "url.path": "/api/v[0-9]+/[a-z]+/[0-9]+" } }
],
"should": [
{ "term": { "http.response.status_code": 200 } },
{ "term": { "http.response.status_code": 403 } },
{ "term": { "http.response.status_code": 401 } }
]
}
},
"threshold": {
"field": ["source.ip"],
"value": 50,
"cardinality": [
{ "field": "url.path", "value": 20 }
]
},
"schedule": { "interval": "5m" },
"severity": "high",
"risk_score": 73,
"tags": ["OWASP-API1", "BOLA", "Enumeration"]
}
}
#!/usr/bin/env python3
"""API Enumeration Attack Detector
Analyzes API access logs to detect enumeration patterns
including BOLA, IDOR, and sequential ID probing.
"""
import re
import sys
import json
from collections import defaultdict
from datetime import datetime, timedelta
from dataclasses import dataclass, field
from typing import List, Dict, Optional
@dataclass
class AccessRecord:
timestamp: datetime
source_ip: str
user_id: Optional[str]
method: str
path: str
status_code: int
object_id: Optional[str] = None
@dataclass
class EnumerationAlert:
source_ip: str
user_id: Optional[str]
endpoint_pattern: str
unique_object_ids: int
total_requests: int
time_window_seconds: float
requests_per_second: float
auth_failure_ratio: float
severity: str
attack_type: str
sample_ids: List[str] = field(default_factory=list)
class EnumerationDetector:
# Regex patterns for extracting object IDs from API paths
ID_PATTERNS = [
re.compile(r'/api/v\d+/(\w+)/(\d+)'), # Numeric IDs
re.compile(r'/api/v\d+/(\w+)/([a-f0-9\-]{36})'), # UUIDs
re.compile(r'/api/v\d+/(\w+)/([a-zA-Z0-9]{20,})'), # Long alphanumeric IDs
]
def __init__(self, time_window_minutes: int = 5,
min_unique_ids: int = 15,
max_requests_per_second: float = 5.0):
self.time_window = timedelta(minutes=time_window_minutes)
self.min_unique_ids = min_unique_ids
self.max_rps = max_requests_per_second
self.access_log: List[AccessRecord] = []
def parse_log_line(self, line: str) -> Optional[AccessRecord]:
"""Parse a common log format line into an AccessRecord."""
log_pattern = re.compile(
r'(?P<ip>[\d.]+)\s+\S+\s+(?P<user>\S+)\s+'
r'\[(?P<time>[^\]]+)\]\s+'
r'"(?P<method>\w+)\s+(?P<path>\S+)\s+\S+"\s+'
r'(?P<status>\d+)'
)
match = log_pattern.match(line)
if not match:
return None
path = match.group('path')
object_id = None
for pattern in self.ID_PATTERNS:
id_match = pattern.search(path)
if id_match:
object_id = id_match.group(2)
break
return AccessRecord(
timestamp=datetime.strptime(match.group('time'), '%d/%b/%Y:%H:%M:%S %z'),
source_ip=match.group('ip'),
user_id=match.group('user') if match.group('user') != '-' else None,
method=match.group('method'),
path=path,
status_code=int(match.group('status')),
object_id=object_id
)
def analyze(self, records: List[AccessRecord]) -> List[EnumerationAlert]:
"""Analyze access records for enumeration patterns."""
alerts = []
# Group by source IP and endpoint pattern
grouped = defaultdict(list)
for record in records:
if record.object_id:
# Normalize endpoint by removing the specific object ID
endpoint = re.sub(r'/[a-f0-9\-]{36}', '/{id}',
re.sub(r'/\d+', '/{id}', record.path))
key = (record.source_ip, record.user_id, endpoint)
grouped[key].append(record)
for (src_ip, user_id, endpoint), records_group in grouped.items():
if len(records_group) < self.min_unique_ids:
continue
# Sort by timestamp
records_group.sort(key=lambda r: r.timestamp)
# Analyze time windows
window_start = 0
for window_start in range(len(records_group)):
window_records = []
for r in records_group[window_start:]:
if r.timestamp - records_group[window_start].timestamp <= self.time_window:
window_records.append(r)
unique_ids = set(r.object_id for r in window_records)
if len(unique_ids) < self.min_unique_ids:
continue
time_span = (window_records[-1].timestamp -
window_records[0].timestamp).total_seconds()
rps = len(window_records) / max(time_span, 1)
auth_failures = sum(1 for r in window_records
if r.status_code in (401, 403))
failure_ratio = auth_failures / len(window_records)
# Determine severity
if len(unique_ids) > 100:
severity = "critical"
elif len(unique_ids) > 50 or failure_ratio > 0.5:
severity = "high"
elif len(unique_ids) > 20:
severity = "medium"
else:
severity = "low"
# Determine attack type
ids_list = sorted([r.object_id for r in window_records
if r.object_id and r.object_id.isdigit()])
is_sequential = self._check_sequential(ids_list)
attack_type = "sequential_enumeration" if is_sequential else "random_enumeration"
alert = EnumerationAlert(
source_ip=src_ip,
user_id=user_id,
endpoint_pattern=endpoint,
unique_object_ids=len(unique_ids),
total_requests=len(window_records),
time_window_seconds=time_span,
requests_per_second=round(rps, 2),
auth_failure_ratio=round(failure_ratio, 2),
severity=severity,
attack_type=attack_type,
sample_ids=list(unique_ids)[:10]
)
alerts.append(alert)
break # One alert per group
return alerts
def _check_sequential(self, ids: List[str]) -> bool:
"""Check if numeric IDs follow a sequential pattern."""
if len(ids) < 5:
return False
try:
numeric_ids = sorted(int(i) for i in ids)
sequential_count = sum(
1 for i in range(1, len(numeric_ids))
if numeric_ids[i] - numeric_ids[i-1] <= 2
)
return sequential_count / len(numeric_ids) > 0.7
except ValueError:
return False
def main():
detector = EnumerationDetector(
time_window_minutes=5,
min_unique_ids=15
)
log_file = sys.argv[1] if len(sys.argv) > 1 else "/var/log/api/access.log"
records = []
with open(log_file, 'r') as f:
for line in f:
record = detector.parse_log_line(line.strip())
if record:
records.append(record)
alerts = detector.analyze(records)
if alerts:
print(f"\n[!] {len(alerts)} enumeration attack(s) detected:\n")
for alert in alerts:
print(f" Source IP: {alert.source_ip}")
print(f" User ID: {alert.user_id}")
print(f" Endpoint: {alert.endpoint_pattern}")
print(f" Unique IDs Accessed: {alert.unique_object_ids}")
print(f" Requests/sec: {alert.requests_per_second}")
print(f" Auth Failure Ratio: {alert.auth_failure_ratio}")
print(f" Attack Type: {alert.attack_type}")
print(f" Severity: {alert.severity.upper()}")
print(f" Sample IDs: {alert.sample_ids}")
print()
else:
print("[+] No enumeration attacks detected.")
if __name__ == "__main__":
main()
# Always validate object ownership at the data layer
def get_user_order(request, order_id):
order = Order.objects.get(id=order_id)
if order.user_id != request.user.id:
raise PermissionDenied("Not authorized to access this order")
return order
import uuid
# Use UUIDs instead of sequential integers
class Order(Model):
id = UUIDField(default=uuid.uuid4, primary_key=True)
# Kong rate limiting per API route
plugins:
- name: rate-limiting
config:
minute: 30
policy: redis
limit_by: credential