Preventive Controls
Controls designed to stop security incidents before they occur. Preventive controls are proactive measures that block threats, restrict access, or eliminate vulnerabilities before they can be exploited.
Understanding Preventive Controls
Preventive controls stop security incidents before they happen. This is the defining characteristic—if the control's purpose is to block, restrict, or eliminate a threat proactively, it's preventive.
Think of preventive controls as the first line of defense. A firewall that blocks malicious traffic prevents the attack from reaching your network. Encryption prevents unauthorized users from reading data even if they access it. A locked door prevents unauthorized physical entry.
The key question: "Does this control stop something bad from happening in the first place?"
Important: Preventive is a control TYPE, not a category. Any control category (technical, managerial, operational, physical) can be preventive. A firewall is a technical preventive control. A background check policy is a managerial preventive control. A security guard denying entry is an operational preventive control. A locked fence is a physical preventive control.
Why This Matters for the Exam
The Security+ exam heavily tests the distinction between preventive and detective controls. This is the most common control type confusion because both seem like they're "stopping" threats.
- •The difference is WHEN they act:
- •Preventive: BEFORE the incident (stops it from happening)
- •Detective: DURING or AFTER the incident (identifies that it happened)
A firewall BLOCKING traffic is preventive—it stops the attack before it succeeds. An IDS ALERTING on traffic is detective—it identifies the attack but doesn't stop it.
This distinction appears in scenario questions where you must choose the right control type for a given situation. If the organization wants to STOP attacks, they need preventive controls. If they want to IDENTIFY attacks, they need detective controls. Most security programs need both.
Deep Dive
Preventive Controls Across All Categories
The exam tests whether you understand that preventive is a TYPE that can exist in any CATEGORY:
Technical Preventive Controls
- •Firewalls blocking unauthorized traffic
- •Encryption protecting data confidentiality
- •Access control lists restricting permissions
- •Antivirus blocking known malware
- •MFA preventing unauthorized authentication
- •Input validation stopping injection attacks
- •Hardening removing unnecessary services
Managerial Preventive Controls
- •Security policies establishing rules
- •Background check requirements
- •Separation of duties policies
- •Acceptable use policies
- •Vendor security requirements
- •Change management procedures
Operational Preventive Controls
- •Security guards denying unauthorized entry
- •Visitor escort procedures
- •Pre-employment screening execution
- •Security awareness training delivery
- •Secure media destruction
Physical Preventive Controls
- •Locks on doors and cabinets
- •Fences around perimeters
- •Mantraps/access control vestibules
- •Bollards blocking vehicle access
- •Biometric access controls
Preventive vs. Detective: The Core Distinction
This is critical for exam success:
| Scenario | Preventive | Detective |
|---|---|---|
| Firewall | Blocks malicious traffic | Logs blocked attempts for review |
| Antivirus | Blocks known malware | Alerts when malware is found |
| IDS/IPS | IPS blocks attacks | IDS alerts on attacks |
| Camera | Visible camera deters (deterrent) | Records incidents for review |
| Lock | Prevents entry | N/A (locks don't detect) |
| Audit log | N/A (logs don't prevent) | Identifies what happened |
Some controls do BOTH:
- •IPS: Prevents (blocks) AND Detects (alerts)
- •Antivirus: Prevents (blocks) AND Detects (alerts)
- •Guards: Prevent (deny entry) AND Detect (observe suspicious behavior)
The Prevention Spectrum
Preventive controls work at different stages:
1. Eliminate the vulnerability — Patching, hardening, removing services 2. Block the attack vector — Firewalls, input validation, encryption 3. Restrict access — Authentication, authorization, physical barriers 4. Reduce opportunity — Separation of duties, least privilege, job rotation
How CompTIA Tests This
Example Analysis
Scenario: An organization implements a web application firewall (WAF) that inspects incoming HTTP requests and blocks any request containing SQL injection patterns before it reaches the database server.
Analysis: This is a preventive control because: • It stops the attack BEFORE it succeeds • The malicious request never reaches the database • The SQL injection is blocked, not just detected
Category: This is a technical control (software/hardware mechanism)
Compare to detective: If the WAF only logged suspicious requests without blocking them, that would be detective. The organization would know about the attack but couldn't stop it with that control alone.
Real-world note: Most WAFs do both—they block AND log. When the exam asks about a specific function, focus on what the question describes. "Blocks requests" = preventive. "Alerts on requests" = detective.
Key Terms to Know
Common Mistakes to Avoid
Exam Tips
Memory Trick
"Preventive = BEFORE. Detective = AFTER."
If you remember nothing else, remember this timing distinction.
- •The Stop vs. Spot Framework:
- •Preventive controls STOP threats
- •Detective controls SPOT threats
- •Verb Clues:
- •Preventive verbs: blocks, prevents, denies, stops, restricts, eliminates
- •Detective verbs: detects, identifies, alerts, logs, monitors, discovers
- •The Bouncer Analogy:
- •Think of a nightclub bouncer:
- •Checking IDs at the door = Preventive (stops underage entry)
- •Watching for fights inside = Detective (identifies problems)
- •Breaking up a fight = Corrective (fixes the problem after it started)
The same bouncer performs different control types at different times.
Test Your Knowledge
Q1.An organization wants to ensure that attackers cannot read sensitive data even if they gain access to the file server. Which preventive control BEST addresses this requirement?
Q2.A firewall is configured to block all inbound traffic on port 23 (Telnet) and log any blocked connection attempts. Which control types does this configuration represent?
Q3.Which of the following is a managerial preventive control?
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