NIST 800-53 vulnerability scanning and remediation timeframes

This is the most urgent situation. A vulnerability that an outside party can reach and that is likely to be exploited sits at the top of the FedRAMP timeframe structure, because it can cause the greatest potential impact to agency data and services. Teams should treat these findings as incidents of prioritization rather than as routine backlog items, and should check whether the flaw appears in the CISA Known Exploited Vulnerabilities catalog, which FedRAMP references when it defines KEVs.

• Confirm reachability: Verify from outside the boundary that the affected service, port or API is actually exposed, not just present in an internal asset record.
• Judge exploitability: Use threat intelligence, public exploit availability and KEV status to decide whether the finding is likely exploitable.
• Mitigate first if needed: Apply a compensating control such as blocking the path, disabling the feature or restricting access to reduce risk while a permanent fix is prepared.
• Remediate and verify: Install the vendor fix or remove the component, then rescan to show the flaw is eliminated.
• Do not add exposure: FedRAMP's rules say providers should not deploy new machine-based resources with KEVs or weaken security to make scanning easier.

Before you start, check the exact timeframe for this class in the current FedRAMP rules, and record whether mitigation or remediation closed the finding.

Here the flaw can be reached from outside, but evidence suggests attackers would struggle to use it, for example because it requires local access, unusual preconditions or a configuration the system does not use. The risk is lower than in the first situation, yet FedRAMP still ties the clock to reachability, so exposure alone keeps the finding on a timed track. Teams often make the mistake of closing these findings as accepted risk without documenting the reasoning that supports the lower exploitability rating.

• Document the exploitability reasoning: Record why the flaw is unlikely to be exploited, citing the attack preconditions and the system configuration that rules them out.
• Reduce exposure where practical: Narrow the reachable surface, such as closing unused ports or limiting source addresses, even when full remediation is scheduled later.
• Apply mitigation with a date: If the fix must wait for a vendor release, use a documented mitigation and track the remaining remediation as an open item.
• Reassess when facts change: Public exploit code or a KEV listing moves the finding into the more urgent situation.
• Keep the rating consistent: Use the same exploitability method across systems so auditors can follow how each finding was classified.

Confirm with your assessor how your organization's exploitability rating will be reviewed before relying on it to select a timeframe.

A vulnerability that cannot be reached from outside the boundary still counts under FedRAMP's rules, but it falls in a different class-based timeframe than an internet-reachable flaw. Internal exposure is not a reason to ignore a finding. Insider access, lateral movement after a compromise and misconfigured segmentation can all turn an internal flaw into a path to sensitive data, so the reachability and exploitability assessment must still be made and recorded for every finding.

• Map the internal paths: Identify which internal segments, accounts or services could reach the affected component, and whether segmentation actually restricts them.
• Assess exploitability separately: An internal flaw that requires valid credentials or chained conditions may rank lower than one with a direct network path.
• Schedule remediation within the class timeframe: Use the timeframe that applies to the internal class, and check the current FedRAMP rules for the exact period.
• Use mitigation when patches lag: Restrict administrative access or isolate the host while a vendor update is tested for side effects, as SI-2 requires.
• Record the closing action: Show whether the finding was remediated by patching or only mitigated, because a mitigated finding still needs a path to full removal.

Ask your assessor how internal segmentation will be evidenced, since the classification depends on it.

FedRAMP separates two actions that teams often use interchangeably. Mitigation reduces a vulnerability's risk and impact, for example by blocking an exploit path or isolating the component. Remediation eliminates the vulnerability itself, usually by installing a fixed version or removing the component. Mitigation can stop the clock on potential agency impact in the short term, but it does not close the underlying flaw, so both actions must be tracked as separate states in the findings record.

• Define the two states: Use one label for mitigated findings and another for remediated findings, and do not allow a finding to close as remediated on the strength of a mitigation alone.
• Keep mitigation evidence: Retain the configuration change, firewall rule or access restriction, along with the date it took effect and the rescan result.
• Track the remaining fix: Attach a plan of action and milestones entry for any mitigated finding that still awaits the vendor fix.
• Verify remediation with a rescan: Show the scan no longer detects the flaw, and keep the output as evidence.
• Ask for the current wording: Confirm the exact definitions and the timeframes that apply to your class in the current FedRAMP rules before writing policy.

Check that your ticketing and reporting tools can record both states, because assessors will ask which action closed each finding.

The organization owns the vulnerability management program and remains accountable for it under RA-5 and SI-2, whatever help it buys. It decides the scan frequency it defines for RA-5, the response times it commits to for remediating legitimate vulnerabilities, and which findings it accepts as risk. Those decisions belong in its own policy and must be approved by people who can answer for them to an assessor and an authorizing official.

• Parameters: Set and document the organization-defined values for RA-5, including the scanning frequency and the trigger for scans when new vulnerabilities are reported.
• Remediation timeframes: Approve the deadlines for fixing findings by severity and exposure, and record who may extend them.
• Risk acceptance: Decide, in writing and with an owner and expiry, which unfixed findings are accepted, mitigated or moved to a plan of action and milestones.
• Exploited vulnerabilities: Define how known exploited vulnerabilities are prioritized and who signs off on exceptions.
• Staffing: Assign named people to triage results, track tickets and answer for the program.

Before engaging anyone, confirm that these owners and decisions already exist on paper, because a partner can configure a process but cannot make these decisions for you.

An implementation partner, such as DeployOpen, configures the scanning tools, integrates them with ticketing and asset inventory, and prepares the runbooks and evidence that show the program works. Its work is defined by a written scope that lists systems, tools, deliverables and handover points. The partner does not decide the organization's risk acceptances, does not set its remediation deadlines and does not certify the outcome.

• Tooling: Deploy and configure self-hosted scanners inside the client's environment, including credentialed scanning where the scope requires it.
• Integration: Connect scan output to asset records, ticket queues and reporting so that findings are traceable from detection to closure.
• Runbooks: Write procedures for scan scheduling, triage, escalation and patch testing that the client's staff can run.
• Evidence: Produce scan configurations, scan logs, ticket histories and reports that the client can hand to an assessor.
• Handover: Train named staff and document what remains the client's responsibility after delivery.

In the written scope, check that each deliverable names the artifact produced and the person who receives it.

An independent assessor or third-party assessment organization (3PAO) tests whether the controls work as documented and issues the assessment report. Where the assessment is under FedRAMP, the assessor's role is defined by that program. The assessor examines evidence, interviews staff and tests samples, and it reports its findings independently of the parties that built the program.

• Testing: The assessor checks scan coverage against the asset inventory, sample findings through their lifecycle and compare remediation dates against approved timeframes.
• Independence: The assessor cannot be the party that configured the tools or wrote the runbooks for the same system.
• Reporting: Only the assessor issues the assessment report and any findings it records.
• Scope: The assessor tests the system as it exists at the assessment date, so evidence gaps appear as findings.

DeployOpen does not issue reports or certifications and does not guarantee assessment results. Ask the assessor for its methodology and sample sizes before the engagement starts.