The answer is to block the external IP address at the firewall and disconnect the workstation from the network. This is the best first action because it immediately stops the ongoing data exfiltration by cutting the network path, while isolating the endpoint preserves volatile evidence and prevents the attacker from destroying logs or pivoting to other systems. On the ISC2 Certified in Cybersecurity CC exam, this scenario tests your understanding of containment as the priority in incident response—before eradication or recovery—and the common trap is choosing to investigate or notify management first, which delays stopping the data loss. Remember the memory tip: "Cut the pipe before you look for the leak." This reinforces that when you detect active exfiltration, your first duty is to sever the connection, not to analyze the traffic or alert the user.
ISC2 CC Security Operations Practice Question
This CC practice question tests your understanding of security operations. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A medium-sized company uses a SIEM solution to collect logs from firewalls, servers, and endpoints. The security team receives an alert indicating a possible data exfiltration: an employee's workstation is sending large amounts of data to an external IP address outside business hours. The employee works in the finance department and has access to sensitive financial records. The SIEM shows the connection is ongoing. The security team must respond immediately to contain the incident while preserving evidence. The company's incident response plan designates the security team as first responders. Which of the following is the BEST first action?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Clue: "immediately / without restart"
Why it matters: Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Block the external IP address at the firewall and disconnect the workstation from the network.
Option B is correct because it stops the data flow and isolates the system, containing the incident. Option A could tip off an attacker if malicious and delays containment. Option C is important but should be performed after containment to preserve evidence. Option D delays response and may allow further damage.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Block the external IP address at the firewall and disconnect the workstation from the network.
Why this is correct
Stops data exfiltration and isolates the system, following incident response best practices.
Clue confirmation
The clue words "best", "first", "immediately / without restart" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
Notify the employee's manager and wait for further instructions.
Why it's wrong here
Delays response and could allow exfiltration to continue; the security team should act first.
✗
Call the employee to ask if they are transferring files for a legitimate business purpose.
Why it's wrong here
Wastes time and could alert an attacker; containment should be immediate.
✗
Take a forensic image of the workstation's hard drive before anything else.
Why it's wrong here
Important for evidence but should be done after containment to prevent further data loss.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A SOC analyst notices unusual lateral movement in the network at 2 AM. The IR playbook dictates: identify and contain (isolate the affected machine), then eradicate (remove the malware), then recover (restore from backup), then document. Skipping containment before eradication risks the attacker regaining access. Questions like this test the sequence and rationale of incident response phases.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CC question in full detail.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CC NAT questions on configuration and troubleshooting.
Security Operations — This question tests Security Operations — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Block the external IP address at the firewall and disconnect the workstation from the network. — Option B is correct because it stops the data flow and isolates the system, containing the incident. Option A could tip off an attacker if malicious and delays containment. Option C is important but should be performed after containment to preserve evidence. Option D delays response and may allow further damage.
What should I do if I get this CC question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CC NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "best", "first", "immediately / without restart". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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