Microsoft Internet Explorer 10 & 11 JScript 9 Engine Remote Code Execution Vulnerability (CVE-2015-2419)
Executive & SecOps Summary
SECOPS ASSESSMENTMicrosoft Internet Explorer 10 and 11 browsers utilizing the JScript 9 scripting engine.
Remote attackers can execute arbitrary code or trigger a denial of service (DoS) via memory corruption by enticing a user to visit a specially crafted website.
Apply the official Microsoft MS15-065 security update immediately, and transition legacy environments to modern, secure browsers.
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Deploy the cumulative security update MS15-065 provided by Microsoft. For managed Windows environments, you can force the installation of the relevant security updates using PowerShell:
# Install and force update for the cumulative security patch via PowerShell
Install-Module PSWindowsUpdate -Force -Verbose
Get-WindowsUpdate -KBArticleID KB3076321 -Install -AcceptAll -AutoReboot2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, disable Internet Explorer or restrict JScript execution using Group Policy Objects (GPO) or registry modifications to mitigate the attack surface:
:: Disable legacy compression features in Internet Explorer via Registry
reg add 'HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_DISABLE_LEGACY_COMPRESSION' /v 'iexplore.exe' /t REG_DWORD /d 1 /f3. Log Audit & IoC Verification Commands
Verify the version of the active jscript.dll on the system to ensure the patch has been successfully applied and the system is no longer vulnerable:
# Check the file version of JScript.dll to verify patch status
$jscriptPath = '${env:SystemRoot}\System32\jscript.dll'
if (Test-Path $jscriptPath) {
$fileVersion = (Get-Item $jscriptPath).VersionInfo.FileVersion
Write-Host 'Active JScript.dll Version:' $fileVersion
} else {
Write-Host 'jscript.dll is not present in System32.'
}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
CVE-2015-2419 is a critical Out-of-bounds Write vulnerability (CWE-787) within the JScript 9 scripting engine of Microsoft Internet Explorer 10 and 11. The root cause lies in improper memory handling during the lifecycle management of specific JavaScript objects or garbage collection routines, allowing the engine to write data outside the allocated buffer boundaries.
2. Exploitation Mechanics & Attack Scenario
An attacker exploits this vulnerability by hosting a malicious web page containing crafted HTML and JavaScript designed to manipulate the heap memory layout (e.g., Heap Spraying). When a vulnerable Internet Explorer browser renders this page, the JScript 9 engine miscalculates memory offsets, leading to memory corruption. This allows the attacker to hijack the execution flow and execute arbitrary shellcode under the security context of the current user.
3. Infrastructure & Business Impact
As a CISA KEV-listed vulnerability, this flaw has been actively exploited in the wild. Successful exploitation grants the attacker full control over the victim's endpoint. In an enterprise environment, this can serve as an initial access vector, leading to lateral movement, credential theft, ransomware deployment, and potential compromise of the entire corporate network.
Official Vendor Advisories & References
JScript 9 in Microsoft Internet Explorer 10 and 11 allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption) via a crafted web site, aka "JScript9 Memory Corruption Vulnerability."
Frequently Asked SecOps Questions (CVE-2015-2419)
FAQQ1. How critical is CVE-2015-2419 and is it actively exploited in the wild?
CVE-2015-2419 is rated CVSS 8.8 (HIGH) with a 30-day EPSS exploitation probability of 53.0%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2015-2419?
Primary impacted vendors include microsoft across internet_explorer, jscript. Scope summary: Microsoft Internet Explorer 10 and 11 with JScript 9 engine
Q3. What temporary mitigations or workarounds exist for CVE-2015-2419 before patching?
[Mitigation] Apply the official Microsoft MS15-065 security update immediately, and transition legacy environments to modern, secure browsers. 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-2015-2419
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