26zl Performing Endpoint Vulnerability Remediation
When to Use
Use this skill when:
- Remediating vulnerabilities identified by scanners (Nessus, Qualys, Rapid7)
- Responding to zero-day CVE advisories requiring immediate patching
- Maintaining compliance with patch management SLAs (critical within 14 days, high within 30 days)
- Building a prioritized remediation plan from vulnerability scan results
Do not use this skill for vulnerability scanning itself (use scanning tools) or for application-layer vulnerability remediation (use DevSecOps processes).
Prerequisites
- Vulnerability scan results (Nessus, Qualys, or Rapid7 export in CSV/XML format)
- Patch management platform (WSUS, SCCM, Intune, or third-party like Automox)
- Administrative access to target endpoints or deployment infrastructure
- Change management process for production endpoint patching
- Testing environment for patch validation before production rollout
Workflow
Step 1: Import and Prioritize Vulnerability Findings
Priority scoring combines:
1. CVSS Base Score (0-10)
2. EPSS (Exploit Prediction Scoring System) - probability of exploitation
3. CISA KEV (Known Exploited Vulnerabilities) catalog membership
4. Asset criticality (business impact of affected endpoint)
5. Network exposure (internet-facing vs. internal)
Priority Matrix:
P1 (Critical - 14 days SLA):
- CVSS >= 9.0 OR
- Listed in CISA KEV OR
- Active exploitation in the wild + CVSS >= 7.0
P2 (High - 30 days SLA):
- CVSS 7.0-8.9 AND
- EPSS > 0.5 (50% probability of exploitation)
P3 (Medium - 60 days SLA):
- CVSS 4.0-6.9 OR
- CVSS 7.0-8.9 with EPSS < 0.1
P4 (Low - 90 days SLA):
- CVSS < 4.0 AND
- No known exploit
Step 2: Identify Remediation Actions
For each vulnerability, determine the appropriate remediation:
Remediation Types:
1. Patch: Apply vendor security update (most common)
2. Configuration change: Modify settings to mitigate (registry, GPO)
3. Upgrade: Update to newer software version
4. Workaround: Apply temporary mitigation when patch unavailable
5. Compensating control: Network segmentation, WAF rule, EDR rule
6. Accept risk: Document accepted risk with CISO sign-off
Step 3: Deploy Patches via WSUS/SCCM
# WSUS: Approve patches for deployment
# 1. Open WSUS Console
# 2. Navigate to Updates → Security Updates
# 3. Approve selected KBs for target computer groups
# SCCM: Create Software Update Group
# 1. Software Library → Software Updates → All Software Updates
# 2. Select required KBs → Create Software Update Group
# 3. Deploy to target collection with maintenance window
# Intune: Create Windows Update Ring
# Devices → Windows → Update rings
# Configure: Quality updates deferral = 0 days (for critical)
# Feature updates deferral = per policy
# PowerShell: Force Windows Update check
Install-Module PSWindowsUpdate -Force
Get-WindowsUpdate -KBArticleID "KB5034441" -Install -AcceptAll -AutoReboot
# Verify patch installation
Get-HotFix -Id "KB5034441"
systeminfo | findstr "KB5034441"
Step 4: Apply Configuration-Based Remediations
# Example: Disable SMBv1 (CVE-2017-0144 - EternalBlue)
Set-SmbServerConfiguration -EnableSMB1Protocol $false -Force
Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol -NoRestart
# Example: Disable Print Spooler on non-print servers (CVE-2021-34527 - PrintNightmare)
Stop-Service -Name Spooler -Force
Set-Service -Name Spooler -StartupType Disabled
# Example: Disable LLMNR (credential theft mitigation)
# Via GPO: Computer Configuration → Admin Templates → Network → DNS Client
# Turn off multicast name resolution: Enabled
New-ItemProperty -Path "HKLM:\SOFTWARE\Policies\Microsoft\Windows NT\DNSClient" `
-Name EnableMulticast -Value 0 -PropertyType DWORD -Force
# Example: Restrict NTLM authentication
# Via GPO: Security Settings → Local Policies → Security Options
# Network security: Restrict NTLM: Audit/Deny
Step 5: Handle Zero-Day Vulnerabilities (No Patch Available)
When vendor patch is not yet available:
1. Check vendor advisory for workarounds
- Microsoft: https://msrc.microsoft.com/update-guide
- Adobe: https://helpx.adobe.com/security.html
- Linux: Distribution security trackers
2. Apply temporary mitigations:
- Disable vulnerable feature/service
- Deploy EDR detection rule for exploitation attempt
- Apply network-level blocking (WAF/firewall rules)
- Restrict access to vulnerable application
3. Monitor for patch release:
- Subscribe to vendor security mailing list
- Monitor CISA KEV additions
- Set calendar reminder for next Patch Tuesday
4. Document workaround with expiration date
Step 6: Validate Remediation
# Re-scan remediated endpoints to confirm vulnerability closure
# Option 1: Targeted vulnerability scan
nessuscli scan --target 192.168.1.0/24 --plugin-id 12345
# Option 2: PowerShell verification
# Check specific KB is installed
$kb = Get-HotFix -Id "KB5034441" -ErrorAction SilentlyContinue
if ($kb) {
Write-Host "PASS: KB5034441 installed on $(hostname)" -ForegroundColor Green
} else {
Write-Host "FAIL: KB5034441 missing on $(hostname)" -ForegroundColor Red
}
# Check service is disabled
$svc = Get-Service -Name Spooler
if ($svc.StartType -eq 'Disabled') {
Write-Host "PASS: Print Spooler disabled" -ForegroundColor Green
}
# Check registry configuration
$val = Get-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters" `
-Name SMB1 -ErrorAction SilentlyContinue
if ($val.SMB1 -eq 0) {
Write-Host "PASS: SMBv1 disabled" -ForegroundColor Green
}
Step 7: Report and Track
Generate remediation status report:
Remediation Metrics:
- Total vulnerabilities: X
- Remediated: Y (Z%)
- Pending (within SLA): A
- Overdue (past SLA): B
- Accepted risk: C
- Mean time to remediate (MTTR): D days
- SLA compliance rate: E%
Key Concepts
| Term | Definition |
|---|---|
| CVSS | Common Vulnerability Scoring System; 0-10 severity scale for vulnerabilities |
| EPSS | Exploit Prediction Scoring System; probability (0-1) that a CVE will be exploited in the wild within 30 days |
| CISA KEV | CISA Known Exploited Vulnerabilities catalog; federal mandate to patch these CVEs within specified timeframes |
| SLA | Service Level Agreement for remediation timelines based on vulnerability severity |
| MTTR | Mean Time To Remediate; average days from vulnerability discovery to confirmed fix |
| Compensating Control | Alternative security measure when direct remediation is not feasible |
Tools & Systems
- Nessus/Tenable.io: Vulnerability scanning and remediation tracking
- Qualys VMDR: Vulnerability management, detection, and response platform
- Rapid7 InsightVM: Vulnerability assessment with live dashboards
- WSUS/SCCM/Intune: Microsoft patch deployment infrastructure
- Automox: Cloud-native patch management for Windows, macOS, Linux
- CISA KEV Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
Common Pitfalls
- Patching without testing: Apply patches to a test group first. Some patches cause application compatibility issues or BSOD.
- Ignoring EPSS scores: A CVSS 9.8 vulnerability with EPSS 0.01 may be less urgent than a CVSS 7.5 with EPSS 0.95 (actively exploited).
- Not validating remediation: Deploying a patch does not guarantee installation. Always re-scan to confirm closure.
- Excluding critical servers from patching: Servers that "cannot be rebooted" accumulate critical vulnerabilities. Schedule maintenance windows.
- Treating all CVEs equally: Risk-based prioritization (CVSS + EPSS + asset criticality + exposure) is more effective than patching all criticals first.