Prioritize CISA KEV first when a vulnerability in your environment is listed, use EPSS to rank vulnerabilities without confirmed exploitation evidence, and use CVSS to understand technical severity and potential impact. No one signal is a complete measure of your organization’s risk. Before scheduling a fix, account for whether the vulnerable component is present and reachable, the asset’s exposure and business importance, available controls, and remediation capacity.
So, should you prioritize CVSS, EPSS, or CISA KEV when deciding what to patch first? Treat them as complementary inputs—not competing scores—and keep their different meanings clear.
What CVSS, EPSS, and KEV each tell you
| Signal | What it tells you | Best use | Key limitation |
|---|---|---|---|
| CVSS | The technical characteristics and severity of a vulnerability. The Base group describes its intrinsic characteristics; Environmental scoring can incorporate organization-specific context. | Understand potential technical impact. Review the vector and underlying metrics, not only the headline score. | A Base score alone is not organizational risk and should not be the sole patch-priority rule. FIRST CVSS v3.1 User Guide; FIRST CVSS v4.0 FAQ |
| EPSS | A data-driven estimate from 0 to 1 of the probability that a published CVE will be exploited in the wild in the next 30 days. Scores and percentiles are published daily. | Rank vulnerabilities when direct exploitation evidence is absent; choose thresholds that fit your capacity and risk tolerance. | It is a forecast, not a guarantee about an individual vulnerability, and does not replace local exposure or impact context. FIRST EPSS; FIRST EPSS FAQ |
| CISA KEV | A living catalog of CVEs for which CISA reports evidence of active exploitation. | Use inclusion as a strong prioritization trigger. Federal Civilian Executive Branch (FCEB) agencies covered by BOD 22-01 must meet the listed due dates; CISA urges other organizations to prioritize timely remediation too. | It is not a complete list of every vulnerability that may be exploited. Catalog inclusion records exploitation evidence; it is not the same thing as an EPSS forecast. CISA Known Exploited Vulnerabilities Catalog |
How to decide what to remediate first
- Check KEV and applicable deadlines. Match the CVE and affected product to your environment, then determine whether a CISA due date applies to your organization. CISA’s BOD 22-01 deadline requirement applies to covered FCEB agencies; other organizations are urged to prioritize catalog entries but are not thereby subject to that federal directive. CISA’s KEV guidance
- Use EPSS to sort the remaining vulnerabilities. A higher score means a higher estimated chance of exploitation in the wild over the next 30 days. Use it to order work where you do not have direct exploitation evidence, and assess how much remediation a proposed cutoff would create before adopting it. FIRST EPSS; FIRST EPSS FAQ
- Use CVSS to understand consequences. Examine the vector and metrics behind the score. Environmental scoring may help express organization-specific context, but a high Base score does not by itself establish that an asset is exposed or that a fix must come before every other task. FIRST CVSS v4.0 FAQ; FIRST CVSS v3.1 User Guide
- Apply local context before scheduling. Confirm that the affected component is installed, determine whether the vulnerable function is reachable and exposed, assess the asset’s business consequence, and consider compensating controls and the effort required to remediate. Use these facts to distinguish an urgent, reachable weakness from a severe vulnerability that is not present or is meaningfully constrained in your environment. FIRST: Using EPSS; FIRST CVSS v3.1 User Guide
- Keep the three signals separate in your decision record. Record the KEV status, EPSS score and date, CVSS score and vector, local exposure, impact, and reason for the chosen priority. Do not multiply CVSS by EPSS and label the result a risk score or exploitation probability; the product has no interpretable meaning. FIRST EPSS FAQ
How to handle thresholds and conflicting signals
There is no universal EPSS cutoff
Choose a threshold based on remediation capacity, risk tolerance, and the assets you operate. Compare the resulting workload with the exploitation coverage the threshold is expected to capture. Threshold translations in FIRST guidance are starting points for programs moving from CVSS-based filtering, not universal policy. FIRST EPSS FAQ; FIRST: Using EPSS
If KEV and EPSS appear to disagree, follow KEV
A CVE can have a low EPSS score and still appear in KEV: EPSS forecasts exploitation over the next 30 days, while KEV records CISA’s evidence of exploitation. They answer different questions. FIRST’s guidance says to follow KEV when the signals conflict. Confirm the affected product and applicable obligations, then prioritize remediation accordingly. FIRST EPSS FAQ; CISA KEV Catalog
Windows Errors? Fix Them Before They Spread
Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallCrashes, No Sound, or Screen Glitches?
Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minute#1 Best Overall
Check EPSS freshness
Because EPSS scores are published daily, check the score date when using one to make an operational decision. The score estimates a 30-day probability; it is not a promise about what will happen to a particular CVE. FIRST EPSS; FIRST EPSS FAQ
Does a high CVSS score mean you need to patch immediately?
Not on its own. CVSS communicates technical severity; it does not establish that the vulnerable product is installed, reachable, exposed, or consequential in your specific environment. FIRST states that CVSS Base scores are not risk and should not be used alone for patch prioritization. Use a high score as a reason to understand the vulnerability and its potential impact, then combine it with KEV status, EPSS, and local context to set priority. FIRST CVSS v4.0 FAQ
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.A practical priority model
- KEV-listed and present in your environment: Treat as a strong priority trigger; meet any applicable CISA due date and account for exposure and business impact.
- Not in KEV, with a higher EPSS score: Move it up the queue in proportion to forecast exploitation likelihood, local exposure, and impact.
- High CVSS but lower EPSS and no KEV listing: Use the CVSS vector to assess technical consequences, then decide priority using reachability, exposure, asset importance, and controls.
- Not present or not reachable: Document the finding and the evidence behind that assessment; reassess if inventory, configuration, or exposure changes.
This model does not produce a synthetic score. It makes the reasons for a remediation decision visible while preserving what each signal actually means.
Quick Recap
Rank #4
Rank #3
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
