Question 828 of 1,152

Threats, Vulnerabilities, and Mitigations →mediumMultiple ChoiceObjective-mapped

Quick Answer

The correct answer is a timing attack, a form of side-channel attack that exploits measurable variations in how long an operation takes. This vulnerability arises because the password comparison function returns false immediately upon the first mismatched byte, so the execution time increases with each correct initial byte an attacker guesses. By carefully measuring these timing differences, an attacker can deduce the correct password hash byte by byte, reducing the search space from exponential to linear. On the Security+ SY0-701 exam, this concept tests your understanding of side-channel attacks and how insecure coding practices in authentication logic can leak sensitive data. A common trap is confusing this with a brute-force or dictionary attack, but the key clue is the observable timing variation. Remember the mnemonic: “Time tells tales” — if execution time varies with input correctness, think timing attack.

SY0-701 Threats, Vulnerabilities, and Mitigations Practice Question

This SY0-701 practice question tests your understanding of threats, vulnerabilities, and mitigations. 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 security analyst is reviewing the source code of a custom authentication service. The service uses a function that compares a user-supplied password to the stored password hash by iterating through each byte and returning false immediately upon the first mismatch. The analyst measures the function's execution time and discovers it varies measurably depending on how many initial bytes match. Which type of attack is this vulnerability most likely to facilitate?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

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: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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.

Question 1mediummultiple choice

Full question →

A
Brute-force attack
Why wrong: A brute-force attack attempts every possible combination of characters, which is computationally expensive and does not leverage timing variations. While an attacker could eventually guess the password, the timing vulnerability specifically enables a more efficient attack.
B
Dictionary attack
Why wrong: A dictionary attack uses a precomputed list of common passwords or phrases, and does not utilize execution time measurements. It relies on the likelihood that users choose weak passwords, not on side-channel information like timing.
C
Replay attack
Why wrong: A replay attack involves intercepting a valid authentication token (such as a session cookie or hashed password) and retransmitting it to impersonate the user. It does not involve manipulating or measuring execution time of a comparison function.
D
Timing attack
A timing attack exploits measurable variations in the time it takes to execute a cryptographic operation. In this case, the early-exit comparison enables an attacker to deduce the correct secret byte by byte, making it the correct classification.

Full breakdown with real-world context →

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

✓

Timing attack

The vulnerability is a timing attack because the comparison function returns false immediately upon the first mismatched byte, causing execution time to vary based on how many initial bytes match. An attacker can measure these timing differences to iteratively guess each byte of the password hash, effectively reducing the search space from exponential to linear. This is a classic side-channel attack that exploits observable timing variations in cryptographic or authentication operations.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Brute-force attack
Why it's wrong here
A brute-force attack attempts every possible combination of characters, which is computationally expensive and does not leverage timing variations. While an attacker could eventually guess the password, the timing vulnerability specifically enables a more efficient attack.
✗
Dictionary attack
Why it's wrong here
A dictionary attack uses a precomputed list of common passwords or phrases, and does not utilize execution time measurements. It relies on the likelihood that users choose weak passwords, not on side-channel information like timing.
✗
Replay attack
Why it's wrong here
A replay attack involves intercepting a valid authentication token (such as a session cookie or hashed password) and retransmitting it to impersonate the user. It does not involve manipulating or measuring execution time of a comparison function.
✓
Timing attack
Why this is correct
A timing attack exploits measurable variations in the time it takes to execute a cryptographic operation. In this case, the early-exit comparison enables an attacker to deduce the correct secret byte by byte, making it the correct classification.
Clue confirmation
The clue words "first", "most likely", "immediately / without restart" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates may confuse a timing attack with a brute-force or dictionary attack, not realizing that the key clue is the measurable variation in execution time due to early exit on mismatch, which is a classic side-channel indicator.

Trap categories for this question

Keyword trap
A dictionary attack uses a precomputed list of common passwords or phrases, and does not utilize execution time measurements. It relies on the likelihood that users choose weak passwords, not on side-channel information like timing.

Detailed technical explanation

How to think about this question

Under the hood, a constant-time comparison function (e.g., using XOR and OR operations) ensures that execution time does not depend on the input, preventing timing leaks. In real-world scenarios, such as verifying HMACs in TLS or password hashes in authentication services, a non-constant-time comparison can allow an attacker to recover secrets byte-by-byte over a network by averaging multiple timing samples. This is why standards like RFC 2104 recommend constant-time verification for MACs.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A security team runs a vulnerability scan on a web application and discovers an unpatched SQL injection flaw. The team prioritises remediation by CVSS score — critical flaws are patched within 24 hours, high within 7 days. Questions like this test whether you understand vulnerability management processes, scanning tools, and remediation prioritisation.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this SY0-701 question test?

Threats, Vulnerabilities, and Mitigations — This question tests Threats, Vulnerabilities, and Mitigations — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Timing attack — The vulnerability is a timing attack because the comparison function returns false immediately upon the first mismatched byte, causing execution time to vary based on how many initial bytes match. An attacker can measure these timing differences to iteratively guess each byte of the password hash, effectively reducing the search space from exponential to linear. This is a classic side-channel attack that exploits observable timing variations in cryptographic or authentication operations.

What should I do if I get this SY0-701 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "first", "most likely", "immediately / without restart". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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