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
A UDP flood consumes bandwidth with connectionless datagrams and involves no HTTP requests or connection pool at all. It is tempting because UDP floods are common volumetric DDoS techniques, but the stem describes HTTP-layer connection exhaustion, which UDP cannot produce.
- ✗
HTTP flood
Why it's wrong here
An HTTP flood sends complete, valid requests at high volume to overwhelm processing capacity; it does not rely on leaving requests incomplete to hold connections open. It is tempting as the obvious HTTP-layer attack, but the stem's incomplete-request mechanism matches a Slowloris-style attack instead.
- ✗
SYN flood
Why it's wrong here
A SYN flood exhausts the TCP backlog with half-open handshakes and never completes an HTTP request, so it cannot explain incomplete HTTP requests holding connections. It is tempting because both attacks exhaust connection resources, but the HTTP-layer mechanism in the stem points elsewhere.
- ✓
Slowloris
Why this is correct
Slowloris opens many partial HTTP requests, sending incomplete headers and never finishing them. The server holds each connection open awaiting the remainder, exhausting its connection pool while consuming minimal attacker bandwidth, matching the incomplete-request symptom described.
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Same concept, more angles
1 more way this is tested on CEH
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
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.