Microsoft Internet Explorer Scripting Engine Memory Corruption Remote Code Execution Vulnerability (CVE-2018-8373) Technical Analysis and Mitigation Guide
Executive & SecOps Summary
SECOPS ASSESSMENTInternet Explorer 9, 10, and 11 running on Microsoft Windows environments.
Successful exploitation allows remote attackers to execute arbitrary code (RCE) with the privileges of the active user by enticing them to visit a specially crafted website.
Apply the official Microsoft cumulative security updates immediately, or disable VBScript execution in Internet Explorer as a temporary workaround.
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Apply the latest cumulative security updates provided by Microsoft. You can force Windows Update to search and install the required security patches using the following PowerShell commands:
# Install and run Windows Update module to apply all pending security patches
Install-Module PSWindowsUpdate -Force -SkipPublisherCheck
Get-WindowsUpdate -AcceptAll -Install -AutoReboot2. Temporary Workaround & Hardening Configuration
If patching cannot be applied immediately, mitigate the risk by disabling VBScript execution in Internet Explorer via the registry to eliminate the attack vector.
:: Disable VBScript execution in Internet Explorer via Registry
reg add 'HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_DISABLE_VBSCRIPT' /v 'iexplore.exe' /t REG_DWORD /d 1 /f3. Log Audit & IoC Verification Commands
Use the following PowerShell script to audit the version of vbscript.dll on the system to verify if the system is running a potentially vulnerable version.
# Audit vbscript.dll file version
$dllPath = Join-Path $env:SystemRoot 'System32\vbscript.dll'
if (Test-Path $dllPath) {
$fileVersion = (Get-Item $dllPath).VersionInfo.FileVersion
Write-Host 'Current vbscript.dll version:' $fileVersion
Write-Host 'Please cross-reference this version with the latest Microsoft Security Bulletin.'
} else {
Write-Host 'vbscript.dll not found on this system.'
}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-2018-8373) is a critical memory corruption vulnerability in the way the scripting engine (specifically the VBScript engine, vbscript.dll) handles objects in memory within Internet Explorer. The root cause lies in an out-of-bounds write (CWE-787) or Use-After-Free condition, where the engine fails to properly validate object lifecycles in memory, allowing attackers to manipulate memory structures.
2. Exploitation Mechanics & Attack Scenario
An attacker exploits this vulnerability by hosting a specially crafted website containing malicious VBScript code or by injecting the script into compromised legitimate websites or malvertising networks. When a user visits the site via Internet Explorer, the browser's rendering engine parses the VBScript, triggering the memory corruption. By carefully grooming the heap layout, the attacker can bypass modern exploit mitigations, hijack the execution flow, and execute arbitrary shellcode on the target system.
3. Infrastructure & Business Impact
As a highly critical vulnerability listed in CISA's Known Exploited Vulnerabilities (KEV) catalog with an EPSS score of 0.6177, this flaw has been actively exploited in the wild. Successful exploitation grants the attacker the same user rights as the current user. If the user is logged on with administrative rights, the attacker can take complete control of the affected system, leading to lateral movement, ransomware deployment, and severe business disruption.
Official Vendor Advisories & References
A remote code execution vulnerability exists in the way that the scripting engine handles objects in memory in Internet Explorer, aka "Scripting Engine Memory Corruption Vulnerability." This affects Internet Explorer 9, Internet Explorer 11, Internet Explorer 10. This CVE ID is unique from CVE-2018-8353, CVE-2018-8355, CVE-2018-8359, CVE-2018-8371, CVE-2018-8372, CVE-2018-8385, CVE-2018-8389, CVE-2018-8390.
Frequently Asked SecOps Questions (CVE-2018-8373)
FAQQ1. How critical is CVE-2018-8373 and is it actively exploited in the wild?
CVE-2018-8373 is rated CVSS 7.5 (HIGH) with a 30-day EPSS exploitation probability of 61.8%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2018-8373?
Primary impacted vendors include microsoft across internet_explorer. Scope summary: Internet Explorer 9, Internet Explorer 10, and Internet Explorer 11
Q3. What temporary mitigations or workarounds exist for CVE-2018-8373 before patching?
[Mitigation] Apply the official Microsoft cumulative security updates immediately, or disable VBScript execution in Internet Explorer as a temporary workaround. Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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