Collecting Indicators of Compromise

When to Use

During active incident response to identify and block adversary infrastructure
Post-incident to document all observed adversary artifacts for future detection
When sharing threat intelligence with ISACs, sector partners, or law enforcement
When building detection rules in SIEM, EDR, or network security tools
When enriching IOCs with threat intelligence context for risk scoring

Do not use for behavioral TTP analysis without accompanying technical indicators; use MITRE ATT&CK mapping for behavioral characterization.

Prerequisites

Access to incident evidence sources: SIEM logs, EDR telemetry, memory dumps, disk images, network captures
Threat intelligence platform (MISP, OpenCTI, ThreatConnect) for IOC management and sharing
IOC enrichment tools: VirusTotal, OTX (AlienVault Open Threat Exchange), Shodan, DomainTools
STIX 2.1 knowledge for structured IOC representation
Sharing agreements with relevant ISACs (FS-ISAC, H-ISAC, IT-ISAC) or sector partners

Workflow

Step 1: Identify IOC Categories

Collect indicators across all categories from incident evidence:

Network Indicators:

IP addresses (C2 servers, staging servers, exfiltration destinations)
Domain names (C2 domains, phishing domains, DGA domains)
URLs (malware download, C2 check-in, exfiltration endpoints)
JA3/JA3S hashes (TLS client/server fingerprints)
User-Agent strings (custom or unusual HTTP headers)
DNS query patterns (tunneling signatures, DGA patterns)

Host Indicators:

File hashes (MD5, SHA-1, SHA-256 of malware, tools, scripts)
File paths (known malware installation directories)
Registry keys (persistence mechanisms, configuration storage)
Scheduled tasks and service names (persistence)
Mutex/event names (malware instance synchronization)
Named pipes (C2 communication channels, e.g., Cobalt Strike)

Email Indicators:

Sender addresses and domains (spoofed or attacker-controlled)
Subject lines and body content patterns
Attachment names and hashes
Embedded URLs
Email header anomalies (SPF/DKIM/DMARC failures)

Step 2: Extract IOCs from Evidence Sources

Systematically extract indicators from each evidence source:

From SIEM/Log Analysis:

# Extract unique destination IPs from firewall logs
index=firewall action=blocked
| stats count by dest_ip
| where count > 100

# Extract domains from DNS query logs
index=dns query=*evil* OR query=*c2*
| stats count by query

From Memory Forensics:

# Extract network connections
vol -f memory.raw windows.netscan | grep ESTABLISHED

# Extract strings from suspicious process memory
vol -f memory.raw windows.memmap --pid 3847 --dump
strings -n 8 pid.3847.dmp | grep -E "(http|https)://"

From Malware Analysis:

Sandbox Report IOC Extraction:
- Dropped files:      3 (hashes extracted)
- DNS queries:        update.evil[.]com, cdn.malware[.]net
- HTTP connections:   POST to https://185.220.101[.]42/gate.php
- Registry modified:  HKCU\Software\Microsoft\Windows\CurrentVersion\Run\svcupdate
- Mutex created:      Global\MTX_0x1234ABCD
- Named pipe:         \\.\pipe\MSSE-1234-server

Step 3: Enrich IOCs with Context

Add threat intelligence context to each indicator:

IOC Enrichment Report:
━━━━━━━━━━━━━━━━━━━━━
IP: 185.220.101.42
  VirusTotal:     12/89 vendors flag as malicious
  Shodan:         Open ports: 443, 8443, 80
  Geolocation:    Netherlands, AS208476
  First Seen:     2025-10-01
  Threat Intel:   Associated with Qakbot C2 infrastructure
  Confidence:     High
  TLP:            AMBER

Domain: update.evil[.]com
  Registration:   2025-10-28 (recently registered)
  Registrar:      Namecheap
  WHOIS Privacy:  Yes
  VirusTotal:     8/89 vendors flag as malicious
  DNS History:    Resolved to 185.220.101.42, 91.215.85.17
  Confidence:     High
  TLP:            AMBER

Step 4: Score and Prioritize IOCs

Assign confidence and risk scores to each indicator:

Score	Confidence Level	Criteria
90-100	Confirmed Malicious	Multiple TI sources confirm, observed in active attack
70-89	Highly Suspicious	Single TI source confirms, behavioral analysis supports
50-69	Suspicious	Limited TI data, contextually suspicious
30-49	Unconfirmed	No TI matches, but anomalous in environment
0-29	Likely Benign	False positive indicators or legitimate infrastructure

Step 5: Distribute IOCs for Detection and Blocking

Push IOCs to defensive systems for immediate protection:

Firewall/IPS: Block C2 IPs and domains
DNS: Sinkhole malicious domains
EDR: Add file hashes to blocklist, create custom IOC watchlists
Email Gateway: Block sender domains, attachment hashes, malicious URLs
SIEM: Create correlation searches for IOC matches
Web Proxy: Block URLs and domains in web filtering policy

Step 6: Share IOCs with Partners

Package IOCs in STIX 2.1 format for sharing:

{
  "type": "indicator",
  "spec_version": "2.1",
  "id": "indicator--a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "created": "2025-11-15T18:00:00Z",
  "modified": "2025-11-15T18:00:00Z",
  "name": "Qakbot C2 Server IP",
  "indicator_types": ["malicious-activity"],
  "pattern": "[ipv4-addr:value = '185.220.101.42']",
  "pattern_type": "stix",
  "valid_from": "2025-11-15T14:23:00Z",
  "confidence": 95,
  "labels": ["c2", "qakbot"],
  "object_marking_refs": ["marking-definition--f88d31f6-486f-44da-b317-01333bde0b82"]
}

Submit to MISP, ISAC portals, and TAXII servers per sharing agreements.

Key Concepts

Term	Definition
IOC (Indicator of Compromise)	Technical artifact observed during a security incident that indicates adversary presence (hash, IP, domain, etc.)
TLP (Traffic Light Protocol)	Standard for classifying the sharing restrictions of threat intelligence: WHITE, GREEN, AMBER, AMBER+STRICT, RED
STIX (Structured Threat Information Expression)	Standard language for representing cyber threat intelligence in a structured, machine-readable format
TAXII (Trusted Automated Exchange of Intelligence Information)	Transport protocol for sharing STIX-formatted threat intelligence between organizations
Confidence Score	Numerical rating (0-100) indicating the analyst's certainty that an indicator is truly malicious
IOC Lifecycle	Process of creating, validating, distributing, and eventually retiring indicators as they lose relevance
Defanging	Practice of modifying malicious URLs and domains in reports to prevent accidental clicks (e.g., evil[.]com)

Tools & Systems

MISP: Open-source threat intelligence sharing platform for managing, storing, and distributing IOCs
VirusTotal: Multi-engine malware scanning and threat intelligence platform for IOC enrichment
OpenCTI: Open-source cyber threat intelligence platform supporting STIX 2.1 natively
Yeti: Open-source platform for organizing observables, indicators, and TTPs
CyberChef: GCHQ's data transformation tool useful for decoding, defanging, and formatting IOCs

Common Scenarios

Scenario: Post-Incident IOC Package for ISAC Sharing

Context: After responding to a Qakbot infection that led to Cobalt Strike deployment, the IR team must package all IOCs for sharing with the Financial Services ISAC (FS-ISAC).

Approach:

Compile all network, host, and email indicators from the investigation
Enrich each IOC with VirusTotal and MISP correlation data
Assign confidence scores based on direct observation vs. secondary correlation
Mark all IOCs with TLP:AMBER for partner sharing
Export as STIX 2.1 bundle and submit to FS-ISAC TAXII feed
Create a human-readable IOC summary report for email distribution

Pitfalls:

Including internal IP addresses or hostnames in shared IOC packages (information leakage)
Sharing IOCs at TLP:WHITE that should be restricted to TLP:AMBER
Not defanging URLs and domains in human-readable reports
Sharing IP addresses of legitimate CDNs or cloud providers as malicious IOCs

Output Format

INDICATOR OF COMPROMISE REPORT
================================
Incident:     INC-2025-1547
Date:         2025-11-15
TLP:          AMBER
Sharing:      FS-ISAC, internal SOC

NETWORK INDICATORS
Type     | Value                    | Confidence | Context
---------|--------------------------|------------|--------
IPv4     | 185.220.101[.]42         | 95         | Qakbot C2 server
IPv4     | 91.215.85[.]17           | 90         | Cobalt Strike C2
Domain   | update.evil[.]com        | 95         | Staging domain
URL      | hxxps://185.220[.]101.42/gate.php | 95  | C2 check-in
JA3      | a0e9f5d64349fb13191bc7...| 80         | Qakbot TLS fingerprint

HOST INDICATORS
Type     | Value                    | Confidence | Context
---------|--------------------------|------------|--------
SHA-256  | a1b2c3d4e5f6...         | 100        | Qakbot dropper
SHA-256  | b2c3d4e5f6a7...         | 100        | Cobalt Strike beacon
FilePath | C:\Users\*\AppData\Local\Temp\update.exe | 85 | Dropper location
RegKey   | HKCU\...\Run\svcupdate  | 90         | Persistence
Mutex    | Global\MTX_0x1234ABCD   | 95         | Qakbot instance lock
Task     | WindowsUpdate           | 90         | Scheduled task persistence

EMAIL INDICATORS
Type     | Value                    | Confidence | Context
---------|--------------------------|------------|--------
Sender   | billing@spoofed[.]com   | 95         | Phishing sender
Subject  | "Invoice-Nov2025"       | 70         | Phishing subject line
Hash     | c3d4e5f6a7b8...         | 100        | Malicious .docm attachment

TOTAL: 14 indicators | HIGH confidence avg: 91