Common Indicators of Compromise (IoCs) and How to Detect Them

In today's dynamic cyber threat landscape, organisations need to proactively monitor for signs of compromise to prevent data breaches, ransomware attacks, and other cyber incidents. Indicators of Compromise (IoCs) provide early warning signs that a system may have been breached or is under attack. By understanding these IoCs and using the right detection tools, Security Operations Centres (SOCs) can quickly identify, investigate, and contain threats before they escalate.

This article explains the concept of IoCs, highlights the most common types, and explores how SOCs use various tools and techniques to detect them in real-time.

1. What Are Indicators of Compromise (IoCs)?

Indicators of Compromise are pieces of evidence or artefacts that suggest a security incident has occurred. These indicators can take many forms, including unusual network traffic, unexpected system changes, or malicious files. By identifying IoCs, security teams can detect and respond to threats before significant damage is done.

IoCs are typically classified into three categories:

1. Host-based IoCs: Found on endpoints, such as computers and servers.

2. Network-based IoCs: Observed in network traffic and communications.

3. Behavioural IoCs: Indicate unusual or suspicious actions by users or systems.

IoCs are often linked to Indicators of Attack (IoAs), which focus on the tactics and techniques used by attackers. Together, these indicators provide a comprehensive view of both current and potential threats.

2. Why Are IoCs Important?

Detecting and analysing IoCs helps organisations:

• Detect Threats Early: Identify threats before they cause extensive damage or data breaches.

• Mitigate Risks: Respond to incidents in real-time, minimising downtime and business impact.

• Prevent Future Attacks: Gain insights into attacker tactics and techniques, improving defence mechanisms.

• Support Compliance: Demonstrate the ability to monitor and manage cyber risks, meeting regulatory requirements such as GDPR, NIS2, and ISO 27001.

Without proper IoC monitoring, organisations are at greater risk of delayed detection, increased damage, and prolonged recovery times.

3. Common Indicators of Compromise

Here are some of the most common IoCs that SOCs monitor:

3.1. Unusual Network Traffic

Changes in network traffic patterns can indicate malicious activity, such as data exfiltration or a Distributed Denial of Service (DDoS) attack.

Examples:

• Large amounts of data being transferred outside normal working hours.

• Unusual communication with known malicious IP addresses or domains.

• Unexpected spikes in network traffic from a specific device.

Detection Techniques:

• Use Intrusion Detection Systems (IDS) and Intrusion Prevention Systems (IPS) to monitor network traffic for anomalies.

• Implement network flow analysis tools to track data flows and identify suspicious behaviour.

• Leverage threat intelligence feeds to block communication with known malicious actors.

3.2. Unauthorised Access Attempts

Repeated or unauthorised login attempts may indicate a brute-force attack or compromised credentials.

Examples:

• Multiple failed login attempts from the same IP address or user account.

• Logins from geographically distant locations within a short period (impossible travel).

• Access to privileged accounts without prior authorisation.

Detection Techniques:

• Implement Security Information and Event Management (SIEM) systems to aggregate and analyse login events.

• Use multi-factor authentication (MFA) to prevent unauthorised access.

• Configure alerts for abnormal login patterns and access to sensitive resources.

3.3. Suspicious File Activity

Malware often creates, modifies, or deletes files on a compromised system. Tracking these changes can reveal the presence of malicious software.

Examples:

• Unauthorised changes to system or application files.

• Creation of files with suspicious names or extensions (e.g., .exe, .bat, .vbs).

• Encrypted files, which may indicate ransomware activity.

Detection Techniques:

• Use endpoint detection and response (EDR) tools to monitor file integrity and system changes.

• Implement File Integrity Monitoring (FIM) to detect unauthorised modifications to critical files.

• Scan for known malware signatures using antivirus and anti-malware solutions.

3.4. Unusual User Behaviour

Attackers may compromise user accounts to carry out malicious activities. Monitoring user behaviour can help detect insider threats and account takeovers.

Examples:

• Users accessing systems or files they do not typically use.

• Sudden spikes in data access or downloads.

• Unusual commands executed on a system, such as privilege escalation attempts.

Detection Techniques:

• Implement User and Entity Behaviour Analytics (UEBA) to establish behavioural baselines and detect deviations.

• Use access control logs to track and analyse user activity across critical systems.

• Configure alerts for high-risk actions, such as privilege changes or data exports.

3.5. Malware and Malicious Code

Malicious software can infect endpoints and spread across the network, disrupting operations and compromising data integrity.

Examples:

• Presence of known malware or suspicious executables.

• Processes running from non-standard directories (e.g., temp folders).

• Unexpected communication with command-and-control (C2) servers.

Detection Techniques:

• Use anti-malware tools and threat intelligence feeds to identify known malware signatures.

• Implement sandboxing to analyse suspicious files in a controlled environment.

• Deploy EDR solutions to monitor system processes and block malicious activity.

3.6. Data Exfiltration

Attackers often steal sensitive data as part of their objectives. Detecting data exfiltration early can prevent significant data breaches.

Examples:

• Large or unusual data transfers to external servers.

• Use of encrypted or obfuscated communication channels.

• Access to sensitive data outside normal business hours.

Detection Techniques:

• Implement Data Loss Prevention (DLP) solutions to monitor and block unauthorised data transfers.

• Use network traffic analysis tools to detect abnormal data flows.

• Configure alerts for access to critical data repositories.

4. Tools and Techniques for IoC Detection

SOC teams use a combination of tools and techniques to detect IoCs in real-time, including:

1. Security Information and Event Management (SIEM):
   Aggregates and correlates security logs from multiple sources to identify patterns and anomalies.

2. Endpoint Detection and Response (EDR):
   Provides continuous monitoring and detection of threats on endpoints, such as laptops and servers.

3. Intrusion Detection and Prevention Systems (IDS/IPS):
   Monitors network traffic for signs of malicious activity and can automatically block known threats.

4. Threat Intelligence:
   Integrates external intelligence feeds to identify known malicious IP addresses, domains, and file signatures.

5. User and Entity Behaviour Analytics (UEBA):
   Detects deviations from normal user behaviour that may indicate compromise.

6. File Integrity Monitoring (FIM):
   Tracks changes to critical files and alerts on unauthorised modifications.

5. Best Practices for IoC Management

To maximise the effectiveness of IoC detection, organisations should:

1. Maintain Threat Intelligence: Regularly update threat intelligence feeds to stay informed about new attack techniques and indicators.

2. Automate Detection: Use automated tools to monitor, correlate, and analyse security events in real-time.

3. Prioritise Alerts: Implement a risk-based approach to prioritise alerts and reduce false positives.

4. Conduct Regular Training: Ensure SOC analysts are trained to recognise and respond to IoCs effectively.

5. Perform Continuous Monitoring: Implement 24/7 monitoring to detect threats at any time.

6. Conclusion

Understanding and detecting Indicators of Compromise (IoCs) is essential for effective threat detection and incident response. By monitoring host-based, network-based, and behavioural indicators, SOC teams can quickly identify potential threats, contain incidents, and minimise damage. With the right tools, techniques, and best practices, organisations can strengthen their security posture and reduce the risk of successful cyberattacks.

For expert guidance on implementing IoC detection and SOC operations, contact our cybersecurity specialists today.