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VPC Flow Logs Reference

Senrigan loads Amazon VPC Flow Logs from the same S3 copy as CloudTrail and hunts over them on the 🌊 VPC Flow agent page and the VPC Flow Logs Threat Hunting dashboard.

Setup

Copy the whole AWSLogs/ prefix. Each file is routed by its AWS object name; digests, AWS Config, ELB logs and other files are skipped and counted in the ingest summary.

aws s3 sync s3://<your-bucket>/AWSLogs/ docker/logs/AWSLogs/
make ingest
make up

What is ingested

  • Plain-text flow logs (.log.gz), default or custom format, in the default, hourly or Hive-compatible S3 layout. Every field AWS documents is kept, and fields added by AWS later are preserved.
  • Parquet flow logs are not supported: they are skipped and counted.
  • With GeoLite2 in docker/data/geoip/, every address gets country, city and ASN; ingester enrich fills them in later.

Reading flow evidence

  • A row is one flow observed on one interface in one aggregation window — never a connection. Intra-VPC traffic is observed twice.
  • ACCEPT means a security group or NACL allowed the packets, not that a session was established.
  • Local and remote endpoints are definitive only when the record carries flow-direction (direction_source = 'record').
  • Records rejected by Block Public Access carry no bytes, and traffic_path = 2 means internet gateway or gateway endpoint.
  • Traffic to the Amazon DNS resolver, instance metadata, Time Sync and DHCP is never logged.

🎯 18 built-in hunts — 🌊 VPC Flow page

Every hunt runs without an API key and declares the fields it needs: when the selected data does not log one, the page reports insufficient coverage instead of an empty result.

# Hunt Category Severity
1 🧭 Flow Log Sources and Field Coverage 🧭 Coverage P4
2 🧭 SKIPDATA Gaps by Interface 🧭 Coverage P3
3 🔍 Vertical Port Scans 🔍 Recon P3
4 🔍 Horizontal Sweeps 🔍 Recon P3
5 🚪 Internet Access to Admin / DB Ports 🚪 Exposure P1
6 🚪 Rejected, Then Accepted 🚪 Exposure P2
7 📤 Egress Spike vs Host Baseline 📤 Egress P1
8 📤 Unusual Destination Ports 📤 Egress P2
9 📤 DNS to Non-Amazon Resolvers 📤 Egress P3
10 📤 Outbound SMTP 📤 Egress P3
11 ⏱️ Periodic Observations to External Peers ⏱️ Periodicity P2
12 ↔️ New Internal Admin-Port Pairs ↔️ Lateral Movement P1
13 ↔️ Internal Inbound, Then External Egress ↔️ Lateral Movement P2
14 🧪 Unusual IP Protocols 🧪 Protocols P3
15 🧪 UDP Fan-Out to External Hosts 🧪 Protocols P3
16 🧪 ICMP and ICMPv6 Peers 🧪 Protocols P4
17 🌍 Accepted Inbound by Country 🌍 GeoIP P4
18 🛡️ BPA and Encryption-Control Rejections 🛡️ Posture P3

📊 50-chart dashboard — VPC Flow Logs Threat Hunting

Start with the Coverage tab: it shows which subscriptions, fields and time windows the other tabs can see.

# Chart Tab
1 Flow Log Sources 🧭 Coverage
2 Capture Scope from CloudTrail 🧭 Coverage
3 NODATA / SKIPDATA Windows 🧭 Coverage
4 Records by Direction Source 🧭 Coverage
5 Field Availability by Source 🧭 Coverage
6 Flow Records 🚦 Overview
7 Bytes Observed 🚦 Overview
8 REJECT Ratio 🚦 Overview
9 Distinct External Peers 🚦 Overview
10 Interfaces Observed 🚦 Overview
11 SKIPDATA Windows 🚦 Overview
12 Flow Records by Action 🚦 Overview
13 Bytes by Direction 🚦 Overview
14 Top Rejected External Sources 🔍 Inbound / Recon
15 Vertical Scan Candidates 🔍 Inbound / Recon
16 Horizontal Scan Candidates 🔍 Inbound / Recon
17 Internet to Admin / DB Ports — Accepted 🔍 Inbound / Recon
18 SYN-Only Records from External Sources 🔍 Inbound / Recon
19 REJECT then ACCEPT — Same Peer, Target and Port 🔍 Inbound / Recon
20 Top External Destinations by Bytes 📤 Egress
21 Egress Volume vs Host Baseline 📤 Egress
22 Egress Bytes by Traffic Path 📤 Egress
23 Unusual Destination Ports 📤 Egress
24 DNS to Non-Amazon Resolvers 📤 Egress
25 Outbound SMTP 📤 Egress
26 Long-Running and Low-and-Slow Flows 📤 Egress
27 Periodic Flow-Log Observations ⏱️ Periodicity
28 Internal Admin-Port Traffic ↔️ Lateral Movement
29 First-Seen Internal Pairs ↔️ Lateral Movement
30 Internal Fan-Out by Source ↔️ Lateral Movement
31 Internal Inbound Followed by External Egress ↔️ Lateral Movement
32 ICMP / ICMPv6 Peers 🧪 Protocols & IPv6
33 UDP Fan-Out to External Hosts 🧪 Protocols & IPv6
34 Unusual IP Protocols 🧪 Protocols & IPv6
35 IPv6 Flows 🧪 Protocols & IPv6
36 Inbound Countries 🌍 GeoIP
37 Outbound Countries 🌍 GeoIP
38 External ASNs 🌍 GeoIP
39 Inbound Accepted — Origin Map 🌍 GeoIP
40 Inbound Rejected — Origin Map 🌍 GeoIP
41 Outbound Bytes — Destination Map 🌍 GeoIP
42 Inbound Records by Country and Action 🌍 GeoIP
43 Inbound Accepted Ports by Country 🌍 GeoIP
44 Top Outbound ASNs by Bytes 🌍 GeoIP
45 Rare Outbound Countries 🌍 GeoIP
46 REJECT Reasons (BPA / Encryption Controls) 🛡️ Posture
47 Encryption Status 🛡️ Posture
48 Egress to AWS Services by Path 🛡️ Posture
49 Middlebox Interfaces 🛡️ Posture
50 Egress Heatmap (UTC Hour × Weekday) 🛡️ Posture