Insider Threats - Risks from Within

About 2 min read

An insider threat refers to a security threat caused, intentionally or through negligence, by people inside an organization - employees, contractors, business partners, and so on. Unlike attacks from outside, insider threats originate from individuals who hold legitimate access privileges, making them difficult to detect with a firewall or perimeter defenses. According to Verizon's Data Breach Investigations Report (DBIR), insiders are involved in roughly 20% of data breaches, and the damage per incident tends to exceed that of external attacks.

The Three Types of Insider Threats

Insider threats are broadly classified into three types according to motive and circumstances. Because each type calls for different detection methods and countermeasures, correctly understanding the categories is the starting point of defense.

Detection with UEBA

Traditional rule-based monitoring struggled to spot suspicious behavior that stayed within legitimate privileges. UEBA (User and Entity Behavior Analytics) uses machine learning to learn each user's "normal behavior pattern" as a baseline and detects deviations from it. For example, it automatically scores behavior such as bulk downloads from a file server the user does not usually access, abnormal late-night logins, or a sudden spike in access to confidential folders by an employee whose departure date is near, and it works with a SIEM to raise alerts.

Insider Threat Detection Flow

Managing Departing Employees' Access Privileges

Many insider threat incidents cluster around the period before and after an employee leaves. It is not unusual for an employee who has decided to resign to take confidential data while still employed. As part of IAM operations, it is important to establish procedures that gradually reduce a departing employee's access privileges and immediately disable all of their accounts on their last working day. You also need to verify that no business data remains in personal cloud-service accounts after they leave.

Relationship to the Principle of Least Privilege

The principle of least privilege is the foundation of insider threat defense. Granting broad access rights to all employees widens the blast radius of malicious actions and raises the probability of accidents caused by negligence. Granting only the minimum privileges needed for the job and preventing the buildup of unnecessary privileges (privilege creep) through regular security audits is the key to containing the damage. Combined with data classification, you can design access control more precisely according to sensitivity.

Common Misconceptions

The belief that "our company is small, so insider threats don't apply to us" is dangerous. The smaller the organization, the laxer the separation of duties tends to be, and a single employee often can access a wide range of systems. Moreover, because insider threats include not only malice but also negligence, this is a separate matter from whether or not you trust your employees. The mechanism of access control should be understood not as "we set it up because we don't trust them" but as "we set it up to maintain trust." The article on insider threat defense explains practical approaches in detail.insider threat books on Amazon are also useful references for practical work.

Real-World Use Cases

"UEBA detected that an employee scheduled to leave had been accessing a design drawing folder they normally never touch, every day starting two weeks before their last working day. Our investigation revealed it was an attempt to exfiltrate data in preparation for a move to a competitor, and we were able to prevent it before any harm was done."

For the security posture of the whole organization, see also the corporate password policy and the startup security checklist.