📖 What is Single Loss Expectancy (SLE)?
Single Loss Expectancy (SLE) is the monetary loss expected each time a specific asset is compromised by a threat. It is calculated by multiplying the asset value by the exposure factor. This value provides the foundation for quantitative risk assessment and determining potential financial impacts.
"Remember that SLE x ARO = ALE. If you see a calculation question on the exam, ensure you identify the cost of a single event before applying the frequency."
📚 Certification: Certified Information Systems Security Professional (CISSP)
🔑 What are the Key Concepts of Single Loss Expectancy (SLE)?
- ▸ Asset Value (AV) represents the total monetary worth of the asset, including acquisition costs, replacement value, and potential lost revenue during downtime.
- ▸ Exposure Factor (EF) is the percentage of loss a realized threat would cause to the asset, expressed as a decimal for calculation purposes.
- ▸ SLE is a fundamental component of quantitative risk assessment, allowing organizations to assign a specific dollar value to a single risk event.
- ▸ The calculation SLE = AV × EF must be completed before determining the Annualized Loss Expectancy (ALE) to ensure accurate financial forecasting.
🎯 How does Single Loss Expectancy (SLE) appear on the CISSP Exam?
You may be asked to calculate the SLE given a specific asset value and an exposure factor, requiring you to multiply the two to find the total monetary loss for a single event.
A scenario might describe a server failure and provide the cost of the hardware and the percentage of data lost, asking you to identify the SLE before calculating ALE.
Expect questions where you must distinguish between SLE and ALE to determine if a proposed security control's annual cost is justified by the potential reduction in yearly loss.
❓ Frequently Asked Questions
Does SLE include the cost of the security control?
No, SLE measures the loss resulting from the threat event itself. The cost of the security control is compared against the ALE to determine the return on investment (ROI) for the mitigation.
How do I handle an Exposure Factor that is 100%?
An EF of 1.0 (100%) indicates that the asset is completely destroyed or lost during a single event. In this case, the SLE is equal to the total Asset Value.
What is the primary difference between SLE and ALE in a business case?
SLE is the cost of a single occurrence, while ALE is the expected yearly cost. Business cases for security budgets typically use ALE to justify spending over a fiscal year.