Microsoft Windows TS WebProxy Directory Traversal Privilege Escalation and IE Sandbox Escape (CVE-2015-0016, MS15-004)
Executive & SecOps Summary
SECOPS ASSESSMENTWindows Vista SP2, 7 SP1, 8, 8.1, Windows Server 2008 R2 SP1, 2012 R2 utilizing the TS WebProxy (TSWbPrxy) component
Remote attackers can bypass the Internet Explorer Protected Mode sandbox (Low Integrity) and execute arbitrary code with Medium Integrity privileges via a crafted executable path
Apply the official Microsoft MS15-004 security update immediately and restrict unauthorized ActiveX control execution
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Deploy the official MS15-004 security update. You can verify and install the corresponding KB patch (e.g., KB3025390) using the following PowerShell commands:
# Check if the MS15-004 patch (KB3025390) is installed
Get-HotFix -Id KB3025390
# If not installed, trigger Windows Update to install the security patch
Start-Service -Name wuauserv
Install-WindowsUpdate -KBArticleID KB3025390 -AcceptAll -AutoReboot2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, disable the TS WebProxy ActiveX control in Internet Explorer by setting the compatibility Kill-Bit in the Windows Registry.
# Set the ActiveX Kill-Bit for TS WebProxy CLSID {1095b0cc-3756-47b8-baa5-ae483c7700d8}
$registryPath = 'HKLM:\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{1095b0cc-3756-47b8-baa5-ae483c7700d8}'
if (-not (Test-Path $registryPath)) {
New-Item -Path $registryPath -Force
}
New-ItemProperty -Path $registryPath -Name 'Compatibility Flags' -Value 0x00000400 -PropertyType DWord -Force3. Log Audit & IoC Verification Commands
Verify the file version of tswbprxy.dll to determine if the system is running a vulnerable version of the library.
# Check the file version of tswbprxy.dll
$sys32Path = "$env:SystemRoot\System32 swbprxy.dll"
if (Test-Path $sys32Path) {
$fileVersion = (Get-Item $sys32Path).VersionInfo.FileVersion
Write-Host 'Current tswbprxy.dll Version:' $fileVersion
# Compare this version against the patched version specified in MS15-004
} else {
Write-Host 'tswbprxy.dll is not present 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-2015-0016) is a directory traversal flaw (CWE-22) residing within the TS WebProxy (TSWbPrxy.dll) component of Microsoft Windows Remote Desktop Services. TS WebProxy is a COM object/ActiveX control designed to proxy remote desktop connections. The root cause lies in the insufficient validation of executable pathnames passed to the component, allowing attackers to inject directory traversal sequences (e.g., '../../') to reference files outside the intended directory structure.
2. Exploitation Mechanics & Attack Scenario
In a typical exploitation scenario, an attacker hosts a malicious web page containing specialized JavaScript that instantiates the vulnerable TSWbPrxy ActiveX control. Although Internet Explorer's Protected Mode restricts the browser process to Low Integrity, the TS WebProxy COM object runs at a higher integrity level (Medium Integrity). By passing a crafted path containing directory traversal characters to the object's execution methods, the attacker forces the proxy to execute an arbitrary payload located on the system or a network share, effectively escaping the IE sandbox and elevating privileges from Low to Medium Integrity.
3. Infrastructure & Business Impact
As a high-severity vulnerability listed in the CISA KEV catalog, CVE-2015-0016 poses a significant threat to legacy Windows environments. Successful exploitation allows remote attackers to achieve reliable sandbox escape and local privilege escalation. This can serve as an initial foothold within an enterprise network, enabling lateral movement, credential harvesting, and the deployment of ransomware or advanced persistent threats (APTs).
Official Vendor Advisories & References
Directory traversal vulnerability in the TS WebProxy (aka TSWbPrxy) component in Microsoft Windows Vista SP2, Windows 7 SP1, Windows Server 2008 R2 SP1, Windows 8, Windows 8.1, Windows Server 2012 Gold and R2, and Windows RT Gold and 8.1 allows remote attackers to gain privileges via a crafted pathname in an executable file, as demonstrated by a transition from Low Integrity to Medium Integrity, aka "Directory Traversal Elevation of Privilege Vulnerability."
Frequently Asked SecOps Questions (CVE-2015-0016)
FAQQ1. How critical is CVE-2015-0016 and is it actively exploited in the wild?
CVE-2015-0016 is rated CVSS 7.8 (HIGH) with a 30-day EPSS exploitation probability of 75.8%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2015-0016?
Primary impacted vendors include microsoft across windows, windows_server. Scope summary: Windows Vista SP2, Windows 7 SP1, Windows Server 2008 R2 SP1, Windows 8, Windows 8.1, Windows Server 2012 Gold and R2, and Windows RT Gold and 8.1
Q3. What temporary mitigations or workarounds exist for CVE-2015-0016 before patching?
[Mitigation] Apply the official Microsoft MS15-004 security update immediately and restrict unauthorized ActiveX control execution 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-2015-0016
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