What it does. Identify ransomware-related network indicators, including C2 beaconing patterns, TOR exit node connections, data exfiltration flows, and encryption key exchange, by analyzing Zeek conn.log and NetFlow data. Use when threat hunting for active ransomware network activity or investigating suspected pre-encryption exfiltration during incident response. Part of mukul975/Anthropic-Cybersecurity-Skills (817 security skills) (mukul975/Anthropic-Cybersecurity-Skills).

Install

• npx skills add mukul975/Anthropic-Cybersecurity-Skills --skill analyzing-ransomware-network-indicators, or copy the skill folder into ~/.claude/skills/analyzing-ransomware-network-indicators/.
• Raw file: curl -sL https://raw.githubusercontent.com/mukul975/Anthropic-Cybersecurity-Skills/HEAD/skills/analyzing-ransomware-network-indicators/SKILL.md

SKILL.md (verbatim)

name: analyzing-ransomware-network-indicators
description: Identify ransomware-related network indicators, including C2 beaconing patterns, TOR exit node connections, data exfiltration flows, and encryption key exchange, by analyzing Zeek conn.log and NetFlow data. Use when threat hunting for active ransomware network activity or investigating suspected pre-encryption exfiltration during incident response.
domain: cybersecurity
subdomain: threat-hunting
tags:
- ransomware
- c2-beaconing
- zeek
- netflow
- tor
- exfiltration
- network-forensics
version: '1.0'
author: mahipal
license: Apache-2.0
d3fend_techniques:
- File Metadata Consistency Validation
- Certificate Analysis
- Application Protocol Command Analysis
- Content Format Conversion
- File Content Analysis
nist_csf:
- DE.CM-01
- DE.AE-02
- DE.AE-07
- ID.RA-05
mitre_attack:
- T1071.001
- T1573
- T1048
- T1567.002
- T1486
mitre_f3:
  version: '1.1'
  tactics:
  - positioning
  - monetization
  techniques:
  - id: T1219
    name: Remote Access Tools
    tactic: positioning
    source: attack
  - id: F1018
    name: Convert to Cryptocurrency
    tactic: monetization
    source: f3
  - id: F1047
    name: Transfer of funds
    tactic: monetization
    source: f3

Analyzing Ransomware Network Indicators

Overview

Before and during ransomware execution, adversaries establish C2 channels, exfiltrate data, and download encryption keys. This skill analyzes Zeek conn.log and NetFlow data to detect beaconing patterns (regular-interval callbacks), connections to known TOR exit nodes, large outbound data transfers, and suspicious DNS activity associated with ransomware families.

When to Use

• When investigating security incidents that require analyzing ransomware network indicators
• 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

• Zeek conn.log files or NetFlow CSV/JSON exports
• Python 3.8+ with standard library
• TOR exit node list (fetched from Tor Project or threat intel feeds)
• Optional: Known ransomware C2 IOC list

Steps

1. Parse Connection Logs — Ingest Zeek conn.log (TSV) or NetFlow records into structured format
2. Detect Beaconing Patterns — Calculate connection interval statistics (mean, stddev, coefficient of variation) to identify periodic callbacks
3. Check TOR Exit Node Connections — Cross-reference destination IPs against current TOR exit node list
4. Identify Data Exfiltration — Flag connections with unusually high outbound byte ratios to external IPs
5. Analyze DNS Patterns — Detect DGA-like domain queries and high-entropy subdomains
6. Score and Correlate — Apply composite risk scoring across all indicator types
7. Generate Report — Produce structured report with timeline and MITRE ATT&CK mapping

Expected Output

• JSON report with beaconing detections and interval statistics
• TOR exit node connection alerts
• Data exfiltration flow analysis
• Composite ransomware risk score with MITRE mapping (T1071, T1573, T1041)

Other files in this skill

• LICENSE
• references/api-reference.md
• scripts/agent.py

references/api-reference.md (verbatim)

Ransomware Network Indicator Analysis API Reference

Zeek conn.log Fields

Beaconing Detection Algorithm

1. Group connections by (src_ip, dst_ip, dst_port)
2. Sort timestamps within each group
3. Calculate intervals: t[i+1] - t[i]
4. Compute statistics:
   - mean_interval = mean(intervals)
   - stddev = stdev(intervals)
   - coefficient_of_variation = stddev / mean_interval
5. Flag as beaconing if CV < 0.3 (regular interval pattern)
   - CV < 0.1 = critical (highly regular)
   - CV 0.1-0.3 = high (moderately regular)

TOR Exit Node Detection

# Fetch current TOR exit node list
curl -s https://check.torproject.org/torbulkexitlist > tor_exits.txt

# Alternative: Dan.me.uk TOR list
curl -s https://www.dan.me.uk/torlist/?exit > tor_exits_alt.txt

# Cross-reference with Zeek conn.log
zeek-cut id.resp_h < conn.log | sort -u | comm -12 - tor_exits_sorted.txt

RITA (Real Intelligence Threat Analytics) for Zeek

# Import Zeek logs into RITA
rita import /opt/zeek/logs/current rita_db

# Analyze beaconing
rita show-beacons rita_db

# Show long connections
rita show-long-connections rita_db

# DNS analysis
rita show-exploded-dns rita_db

Zeek CLI for Live Capture

# Analyze PCAP with Zeek
zeek -r capture.pcap

# Live capture on interface
zeek -i eth0 local.zeek

# Extract conn.log fields
zeek-cut ts id.orig_h id.resp_h id.resp_p orig_bytes resp_bytes < conn.log

MITRE ATT&CK Mapping

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