Microsoft Windows Kernel win32k.sys Stack-based Buffer Overflow Local Privilege Escalation (CVE-2010-4398)
Executive & SecOps Summary
SECOPS ASSESSMENTWindows XP SP2/SP3, Server 2003 SP2, Vista SP1/SP2, Server 2008 Gold/SP2/R2, and Windows 7
Local attackers can exploit this to bypass User Account Control (UAC) and execute arbitrary code with SYSTEM privileges
Apply the official Microsoft security update (MS11-011) and restrict write access to registry keys associated with system fonts
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Deploy the official Microsoft security update MS11-011 (KB2393802) immediately. For legacy systems, verify the patch status using the following command:
# Check if the required security update is installed
$PatchCheck = Get-HotFix -Id KB2393802 -ErrorAction SilentlyContinue
if (-not $PatchCheck) {
Write-Warning 'MS11-011 (KB2393802) is missing. Apply the security update immediately.'
} else {
Write-Host 'MS11-011 patch is already installed on this system.'
}2. Temporary Workaround & Hardening Configuration
If patching cannot be performed immediately, restrict write permissions to the EUDC registry keys to prevent non-privileged users from injecting malicious binary payloads.
# Restrict write access to the EUDC registry path for standard users
$RegistryPath = 'HKCU:\EUDC'
if (Test-Path $RegistryPath) {
Write-Host 'Review and restrict ACLs on HKCU:\EUDC to prevent unauthorized REG_BINARY modifications.'
}3. Log Audit & IoC Verification Commands
Audit the registry for suspicious binary configurations under the EUDC font settings and check the version of win32k.sys.
# Query the registry for EUDC font configurations
Get-ItemProperty -Path 'HKCU:\EUDC\*' -ErrorAction SilentlyContinue
# Retrieve the file version of win32k.sys to verify vulnerability status
$KernelDriver = "$env:windir\System32\win32k.sys"
if (Test-Path $KernelDriver) {
(Get-Item $KernelDriver).VersionInfo | Select-Object FileName, FileVersion
}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
A stack-based buffer overflow vulnerability (CWE-787) exists in the win32k.sys kernel-mode driver in Microsoft Windows. The root cause lies within the handling of the System Default End-User Defined Character (EUDC) font registry settings. When the driver calls the RtlQueryRegistryValues function to retrieve registry data, it fails to properly validate the length of the returned data before copying it into a fixed-size stack buffer, leading to memory corruption.
2. Exploitation Mechanics & Attack Scenario
An attacker with local access can craft a malicious REG_BINARY value for the SystemDefaultEUDCFont registry key. When a system process or API triggers the loading of this font, win32k.sys parses the registry value in the kernel context. The lack of bounds checking allows the crafted binary data to overwrite the kernel stack, including the return address. This enables the attacker to redirect execution flow to shellcode, bypassing User Account Control (UAC) and escalating privileges to NT AUTHORITY\SYSTEM.
3. Infrastructure & Business Impact
As a CISA KEV-listed vulnerability, this flaw has been actively exploited in the wild. Although it requires local execution access, it is highly critical as a secondary stage of an attack chain. Successful exploitation allows complete compromise of the endpoint or server, enabling attackers to disable security controls, install persistent malware, and pivot laterally across the enterprise network.
Official Vendor Advisories & References
Stack-based buffer overflow in the RtlQueryRegistryValues function in win32k.sys in Microsoft Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista SP1 and SP2, Windows Server 2008 Gold, SP2, and R2, and Windows 7 allows local users to gain privileges, and bypass the User Account Control (UAC) feature, via a crafted REG_BINARY value for a SystemDefaultEUDCFont registry key, aka "Driver Improper Interaction with Windows Kernel Vulnerability."
Frequently Asked SecOps Questions (CVE-2010-4398)
FAQQ1. How critical is CVE-2010-4398 and is it actively exploited in the wild?
CVE-2010-4398 is rated CVSS 7.8 (HIGH) with a 30-day EPSS exploitation probability of 8.7%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2010-4398?
Primary impacted vendors include microsoft across windows, windows_server. Scope summary: Windows XP SP2/SP3, Server 2003 SP2, Vista SP1/SP2, Server 2008 Gold/SP2/R2, and Windows 7 (both x86 and x64 architectures)
Q3. What temporary mitigations or workarounds exist for CVE-2010-4398 before patching?
[Mitigation] Apply the official Microsoft security update (MS11-011) and restrict write access to registry keys associated with system fonts Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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