What Is Slowloris? DDoS Attack with Partial HTTP Requests
An organization experiences a DDoS attack where the attacker sends many incomplete HTTP requests that keep connections open, exhausting the server's connection pool. Which attack technique is being used?
Quick Answer
The correct answer is Slowloris, as this attack technique is specifically designed to flood a web server with many incomplete HTTP requests, keeping those connections open and gradually exhausting the server’s connection pool until it can no longer accept legitimate traffic. This works because Slowloris sends partial headers—never completing the request—forcing the server to wait indefinitely, which consumes available sockets. On the Certified Ethical Hacker CEH exam, this question tests your understanding of application-layer DDoS attacks versus network-layer floods; a common trap is confusing Slowloris with a SYN flood, but remember that Slowloris operates at Layer 7 using HTTP, not TCP handshakes. To lock it in, think of the name: “Slow” because it sends data slowly, and “loris” as in the slow-moving primate—a perfect mnemonic for an attack that crawls to cause maximum damage.
⚠ Common exam trap
In CEH, candidates often confuse a SYN flood (TCP layer, half-open connections) with Slowloris (HTTP layer, partial requests). Slowloris keeps connections open by sending incomplete HTTP headers, targeting the application layer, unlike SYN flood which operates at the transport layer.
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
✓
Slowloris
Slowloris is a DDoS attack that works by opening multiple connections to the target server and sending partial HTTP requests, never completing them. The server keeps these connections open waiting for the rest of the request, eventually exhausting the connection pool and denying service to legitimate users. This matches the description of incomplete HTTP requests keeping connections open.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
UDP flood
Why it's wrong here
UDP flood sends many UDP packets, not HTTP requests.
- ✗
HTTP flood
Why it's wrong here
HTTP flood sends many complete requests, not partial ones.
- ✗
SYN flood
Why it's wrong here
SYN flood targets the TCP handshake, not HTTP connections.
- ✓
Slowloris
Why this is correct
Slowloris sends partial HTTP headers slowly, holding connections open until the server's limit is reached.
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1 more way this is tested on CEH
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Variation 1. Which THREE of the following are indicators of a slowloris DDoS attack?
hard- A.ICMP echo replies from random IPs
- ✓ B.Normal traffic volume but connections remain open for a long time
- ✓ C.Many half-open HTTP connections
- ✓ D.Server logs showing incomplete HTTP requests
- E.High volume of UDP packets
Why B: B is correct because a Slowloris DDoS attack works by opening many connections to a target web server and keeping them open for as long as possible, sending partial HTTP requests to tie up server resources. This results in normal traffic volume but with connections that remain open for extended periods, preventing legitimate users from connecting.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CEH practice question is part of Courseiva's free EC-Council certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CEH exam.