Denial Of Service
A denial of service (DoS) attack attempts to make a system or service unavailable by overwhelming it with excessive requests or resource consumption.
“A security attack that is intended to overload the system with requests such that legitimate requests cannot be serviced.”
(Definition reproduced from the ISTQB Glossary. Copyright belongs to ISTQB.)
View the complete ISTQB GlossaryWhat is Denial Of Service?
DoS attacks prevent legitimate users from accessing services by exhausting system resources such as CPU, memory, bandwidth, or connections.
Resource exhaustion: Attackers overload system resources.
Availability impact: Legitimate users experience slow responses or outages.
Testing value: Resilience testing evaluates system behavior during high-load conditions.
Real World Example
An insurance claims platform is connecting a claim intake service, a policy validation service, and a payment approval service.
Each part can look correct in isolation while the handoff between parts still fails. Denial of service helps testers focus on the boundary where data, timing, and responsibility meet.
The tester checks payloads, error handling, retries, missing fields, and the order of service calls instead of only confirming that each screen appears.
The claims flow becomes more dependable because Denial of service exposes defects that only appear when real components collaborate.
Practice Questions
Question 1
Which statement BEST describes Denial of service in the context of ISTQB terminology?
Question 2
A tester needs to explain Denial of service to a non‑technical stakeholder. Which approach is MOST appropriate?
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