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Denial of Service - overwhelming the system

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Denial of service occurs when an attacker causes the system to be unavailable.

Examples include:

• Flooding the network with requests.
• Absorbing memory and CPU processes.
• Crashing data stores with an overwhelming number of requests.

Elements and interactions at risk from denial of service

Element

Name	Shape	Definition
Process		Activity that modifies or redirects input to an output
Data store		Permanent or temporary data storage
Data-flow		Data movement between elements

Interaction

Name	Interaction	Definition
Process -> Process		A task sends data to another task
Process <-> External Entity		A task sends or receives data to or from a user
Process <-> Data Store		A task sends or receives data to or from a data store
Data Flow <-> Trust Boundary		Data is transmitted from a trusted environment to someone over the internet (and vice-versa)

How to prevent denial of service

Availability ensures your system is up and running for users. Examples include:

• Using network access-control lists to control incoming and outgoing traffic.
• Using elastic resources to manage growing or shrinking usage.
• Monitoring the system to detect anomalies.
• Enabling operating-system flags to handle memory and CPU processes.

Common security controls to reduce or eliminate risk

• Access control lists (ACL)
• Filtering
• Quotas
• Authorization
• High availability

Tip

Good question to ask: Are there areas where my service is resource-limited?

Check your knowledge

1.

Which statement describes a potential security control against denial of service?

Sender digitally signs a message so the receiver knows who the message came from

System logs all actions and users to keep everyone accountable

System relies on elastic resources to handle more requests as they arrive

You must answer all questions before checking your work.

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