Windows Kernel Local Elevation of Privilege Vulnerability (CVE-2020-17087) Security Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTMultiple Windows OS versions including Windows 7, 8.1, 10, and Windows Server 2008, 2012, 2016, 2019
Local attackers can escalate privileges to SYSTEM, bypassing security controls and gaining full control of the host
Apply the official Microsoft security patches immediately and restrict unauthorized local access on unpatched systems
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
To remediate this vulnerability, apply the official Microsoft Cumulative Updates (LCU). You can verify the patch status and force updates using PowerShell.
# Check if the November 2020 security patch (e.g., KB4586781, KB4586786) is installed
Get-HotFix | Where-Object { $_.HotFixID -match 'KB4586781|KB4586786|KB4586853|KB4586830' }
# Force Windows Update installation using the PSWindowsUpdate module
Install-Module PSWindowsUpdate -Force -Verbose
Get-WindowsUpdate -AcceptAll -Install -AutoReboot2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, restrict local access to the system and enforce strict privilege separation to prevent unauthorized users from executing arbitrary code.
# Disable the local Guest account to prevent unauthorized local access
Disable-LocalUser -Name 'Guest'
# Restrict local logon rights using security policy configuration
secedit /export /cfg C:\secpol.cfg
# (Review and modify user rights assignment in secpol.cfg, then reapply)
secedit /configure /db C:\windows\security\local.sdb /cfg C:\secpol.cfg /areas USER_RIGHTS3. Log Audit & IoC Verification Commands
Verify the version of the cng.sys driver and audit security event logs for suspicious privilege escalation activities.
# Check the file version of cng.sys
$cngPath = 'C:\Windows\System32\drivers\cng.sys'
if (Test-Path $cngPath) {
$fileVersion = (Get-Item $cngPath).VersionInfo.FileVersion
Write-Host 'Current cng.sys File Version:' $fileVersion
}
# Audit Security Event Logs for suspicious processes spawned with SYSTEM privileges
Get-WinEvent -FilterHashtable @{LogName='Security'; ID=4688} -MaxEvents 100 |
Where-Object { $_.Message -match 'SYSTEM' -and $_.Message -match 'cmd.exe|powershell.exe' }Block Kernel Privilege Escalation & Ransomware Payloads Before You Can Reboot
Protect unpatched Windows, Linux, and macOS workloads against in-memory exploitation and lateral movement with autonomous EDR.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2020-17087) is a pool-based buffer overflow vulnerability located in the Windows Kernel Cryptography Next Generation (CNG) driver (cng.sys). The root cause lies in the incorrect calculation of buffer sizes (CWE-131) within functions such as CfgAdgSequencePoint when processing input parameters. This integer overflow or size mismatch leads to an out-of-bounds write in the kernel pool memory.
2. Exploitation Mechanics & Attack Scenario
An attacker with local access and low-integrity privileges can trigger this vulnerability by sending a specially crafted I/O Control (IOCTL) request to the \Device\CNG device. The kernel driver fails to properly validate the input buffer size, causing a heap buffer overflow in the kernel pool. By carefully structuring the kernel pool layout, the attacker can overwrite adjacent kernel structures (such as process tokens) to escalate privileges to NT AUTHORITY\SYSTEM. This vulnerability was actively exploited in the wild in conjunction with a Chrome sandbox escape vulnerability (CVE-2020-15999).
3. Infrastructure & Business Impact
As a CISA KEV-listed vulnerability, the real-world risk of CVE-2020-17087 is extremely high. If an attacker gains initial access via a remote code execution (RCE) exploit in a web browser or other user-mode application, they can leverage this kernel vulnerability to escape sandboxes and compromise the entire operating system. This can lead to lateral movement within the corporate network, deployment of ransomware, and complete data exfiltration.
Official Vendor Advisories & References
Windows Kernel Local Elevation of Privilege Vulnerability
Frequently Asked SecOps Questions (CVE-2020-17087)
FAQQ1. How critical is CVE-2020-17087 and is it actively exploited in the wild?
CVE-2020-17087 is rated CVSS 7.8 (HIGH) with a 30-day EPSS exploitation probability of 5.4%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2020-17087?
Primary impacted vendors include microsoft across windows, windows_kernel. Scope summary: Windows 7, 8.1, 10, and Windows Server 2008, 2012, 2016, 2019, 20H2, and other legacy Windows OS versions
Q3. What temporary mitigations or workarounds exist for CVE-2020-17087 before patching?
[Mitigation] Apply the official Microsoft security patches immediately and restrict unauthorized local access on unpatched systems Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2020-17087
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