Microsoft Internet Explorer Scripting Engine Use-After-Free Remote Code Execution Vulnerability (CVE-2020-0674)
Executive & SecOps Summary
SECOPS ASSESSMENTInternet Explorer 9, 10, and 11 running on various Windows operating system environments
Remote attackers can execute arbitrary code with the privileges of the current user by enticing a victim to view a specially crafted website
Apply the official Microsoft cumulative security updates immediately, or restrict access to the legacy scripting engine (jscript.dll) as a temporary workaround
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
The primary remediation is to apply the official cumulative security updates provided by Microsoft. Ensure Windows Update is enabled and fully patched, or transition to modern browsers like Microsoft Edge.
2. Temporary Workaround & Hardening Configuration
If patching cannot be immediately deployed, restrict access to jscript.dll to prevent the legacy scripting engine from being loaded by the browser.
# Restricting access to 64-bit jscript.dll (and 32-bit on 32-bit systems)
takeown /f 'C:\Windows\System32\jscript.dll'
icacls 'C:\Windows\System32\jscript.dll' /deny everyone:(F)
# Restricting access to 32-bit jscript.dll on 64-bit systems
takeown /f 'C:\Windows\SysWOW64\jscript.dll'
icacls 'C:\Windows\SysWOW64\jscript.dll' /deny everyone:(F)3. Log Audit & IoC Verification Commands
Use the following PowerShell script to verify the file version and check if the workaround restriction has been successfully applied to jscript.dll.
# Check jscript.dll version and ACL status
$paths = @('C:\Windows\System32\jscript.dll', 'C:\Windows\SysWOW64\jscript.dll')
foreach ($path in $paths) {
if (Test-Path $path) {
$version = (Get-Item $path).VersionInfo.FileVersion
$acl = Get-Acl $path | Select-Object -ExpandProperty Access | Where-Object { $_.IdentityReference -like '*Everyone*' }
Write-Host 'Path: ' $path
Write-Host 'Version: ' $version
Write-Host 'Deny Rule Configured: ' ($acl -ne $null)
Write-Host '------------------------------------'
}
}Block Kernel Privilege Escalation & Ransomware Payloads Before You Can Reboot
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability is a Use-After-Free (UAF) flaw that exists in the way the legacy scripting engine, jscript.dll, handles objects in memory within Internet Explorer. Due to a flaw in the garbage collection mechanism, a pointer to a JavaScript object remains valid even after the object itself has been freed from memory. This dangling pointer allows subsequent memory corruption and hijacking of the execution flow.
2. Exploitation Mechanics & Attack Scenario
An attacker exploits this vulnerability by hosting a specially crafted website containing malicious JavaScript designed to trigger the UAF condition. When a user visits the site using an affected version of Internet Explorer, the script allocates and frees specific memory structures. The attacker then fills the freed memory space with controlled shellcode, hijacking the program's control flow to bypass the browser sandbox and execute arbitrary commands.
3. Infrastructure & Business Impact
As a high-severity vulnerability listed in the CISA KEV catalog, this flaw has been actively exploited in the wild. Successful exploitation grants the attacker the same user rights as the current user. If the current user is logged on with administrative rights, the attacker can take complete control of the affected system, potentially leading to lateral movement, ransomware deployment, and severe data breaches.
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 CVE ID is unique from CVE-2020-0673, CVE-2020-0710, CVE-2020-0711, CVE-2020-0712, CVE-2020-0713, CVE-2020-0767.
Frequently Asked SecOps Questions (CVE-2020-0674)
FAQQ1. How critical is CVE-2020-0674 and is it actively exploited in the wild?
CVE-2020-0674 is rated CVSS 7.5 (HIGH) with a 30-day EPSS exploitation probability of 86.9%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2020-0674?
Primary impacted vendors include microsoft across internet explorer, windows. Scope summary: Internet Explorer 9, 10, and 11 on supported versions of Windows client and server operating systems
Q3. What temporary mitigations or workarounds exist for CVE-2020-0674 before patching?
[Mitigation] Apply the official Microsoft cumulative security updates immediately, or restrict access to the legacy scripting engine (jscript.dll) 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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