- A
Alert when multiple failed logins from a single source IP are followed by a successful login from that IP within 10 minutes.
This correlation rule accurately detects the credential stuffing pattern across different accounts from one IP.
- B
Alert when a user account has three failed logins within 5 minutes followed by a successful login.
Why wrong: This targets multiple failures on one account, but the attack uses multiple accounts from one IP.
- C
Alert when a successful authentication occurs immediately after a password reset.
Why wrong: This indicates a possible account takeover after reset, not the described pattern.
- D
Alert on any single failed login attempt from an external IP.
Why wrong: A single failure is too noisy and not indicative of the attack.
Quick Answer
The answer is a correlation rule that alerts when multiple failed logins from a single source IP are followed by a successful login from that IP within a short time window, such as 10 minutes. This is the most effective SIEM rule for credential stuffing detection because it directly captures the attacker’s pattern of testing stolen credentials against many accounts from one IP, then using a valid one to log in. On the CompTIA SecurityX CAS-004 exam, this scenario tests your ability to distinguish between simple threshold rules and correlation rules that chain events across time and entities—a common trap is choosing a rule that only counts failures for a single user, which misses the source-IP pivot. Remember the mnemonic “One IP, many fails, then one win” to recall that credential stuffing always involves a single attacker source succeeding after a spray of attempts.
CAS-004 Security Operations Practice Question
This CAS-004 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 financial organization's SOC analysts have observed repeated failed authentication attempts from a single external IP address against multiple user accounts, followed by a successful authentication from the same IP using one of those accounts. Which type of security monitoring rule would be most effective at detecting this attack pattern in real time?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Alert when multiple failed logins from a single source IP are followed by a successful login from that IP within 10 minutes.
The attack pattern involves brute-force attempts followed by a success, which is a classic credential stuffing attack. Option C is a correlation rule that combines multiple failed logins with a subsequent success for the same source IP, which directly captures this behavior. Option A only detects a single failed login, not the pattern. Option B detects a success after failures but for a single target user, not the source IP pattern. Option D detects a single login after a reset, which is unrelated.
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.
- ✓
Alert when multiple failed logins from a single source IP are followed by a successful login from that IP within 10 minutes.
Why this is correct
This correlation rule accurately detects the credential stuffing pattern across different accounts from one IP.
Related concept
Static NAT maps one inside address to one outside address.
- ✗
Alert when a user account has three failed logins within 5 minutes followed by a successful login.
Why it's wrong here
This targets multiple failures on one account, but the attack uses multiple accounts from one IP.
- ✗
Alert when a successful authentication occurs immediately after a password reset.
Why it's wrong here
This indicates a possible account takeover after reset, not the described pattern.
- ✗
Alert on any single failed login attempt from an external IP.
Why it's wrong here
A single failure is too noisy and not indicative of the attack.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
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 CAS-004 NAT questions on configuration and troubleshooting.
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FAQ
Questions learners often ask
What does this CAS-004 question test?
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: Alert when multiple failed logins from a single source IP are followed by a successful login from that IP within 10 minutes. — The attack pattern involves brute-force attempts followed by a success, which is a classic credential stuffing attack. Option C is a correlation rule that combines multiple failed logins with a subsequent success for the same source IP, which directly captures this behavior. Option A only detects a single failed login, not the pattern. Option B detects a success after failures but for a single target user, not the source IP pattern. Option D detects a single login after a reset, which is unrelated.
What should I do if I get this CAS-004 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 CAS-004 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 24, 2026
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