CVE-2020-1027: Windows 10 1507 Privilege Escalation Flaw

CVE-2020-1027 Overview

CVE-2020-1027 is an elevation of privilege vulnerability that exists in the way the Windows Kernel handles objects in memory. This vulnerability, classified as CWE-787 (Out-of-Bounds Write), allows a local attacker with low privileges to execute code with elevated permissions on affected Windows systems. The vulnerability has been actively exploited in the wild and is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, making it a critical priority for organizations to address.

Critical Impact

This kernel-level vulnerability enables attackers to escalate privileges to SYSTEM level, potentially leading to complete system compromise. Active exploitation has been confirmed in the wild.

Affected Products

• Microsoft Windows 10 (versions 1507, 1607, 1709, 1803, 1809, 1903, 1909)
• Microsoft Windows 7 SP1, Windows 8.1, Windows RT 8.1
• Microsoft Windows Server 2008 SP2, 2008 R2 SP1, 2012, 2012 R2, 2016, 2019
• Microsoft Windows Server versions 1803, 1903, 1909

Discovery Timeline

• April 15, 2020 - CVE-2020-1027 published to NVD
• October 29, 2025 - Last updated in NVD database

Technical Details for CVE-2020-1027

Vulnerability Analysis

This vulnerability resides in the Windows kernel's object handling mechanism, specifically within the sxs (Side-by-Side) assembly component. The flaw manifests as a heap buffer overflow in the CNodeFactory::XMLParser_Element_doc_assembly_assemblyIdentity function, which improperly handles memory when parsing assembly identity elements. When exploited, the out-of-bounds write condition allows attackers to corrupt kernel memory structures, ultimately enabling arbitrary code execution with SYSTEM privileges.

The vulnerability requires local access and low privileges to exploit, but does not require user interaction. This makes it particularly dangerous in scenarios where attackers have already gained initial access to a system through other means, as it provides a reliable path to full system compromise.

Root Cause

The root cause of CVE-2020-1027 is improper bounds checking within the Windows kernel's memory object handling routines. Specifically, the CNodeFactory XML parser fails to properly validate the size of input data when processing assembly identity elements, leading to a heap buffer overflow condition. This out-of-bounds write (CWE-787) occurs when the kernel allocates insufficient buffer space for the processed data, allowing attacker-controlled data to overwrite adjacent heap memory.

Attack Vector

The attack vector for CVE-2020-1027 is local, requiring an attacker to have the ability to execute code on the target system. The exploitation flow typically involves:

1. An attacker with low-privilege access creates a malicious assembly manifest or XML structure
2. The crafted input triggers the vulnerable XML parsing function in the Windows SxS component
3. The heap buffer overflow allows the attacker to corrupt kernel memory structures
4. By carefully controlling the overflow data, the attacker can achieve arbitrary code execution in kernel context
5. The attacker gains SYSTEM-level privileges, bypassing all user-level security restrictions

Technical details regarding the heap buffer overflow in CNodeFactory::XMLParser_Element_doc_assembly_assemblyIdentity are documented in the Packet Storm Security advisory.

Detection Methods for CVE-2020-1027

Indicators of Compromise

• Unexpected SYSTEM-level processes spawned from lower-privilege user contexts
• Anomalous kernel memory access patterns or crash dumps related to sxs.dll or CNodeFactory
• Suspicious assembly manifest files or XML structures in user-writable directories
• Process execution events showing privilege escalation without legitimate elevation requests

Detection Strategies

• Monitor for unusual kernel-mode exceptions or blue screen events related to memory corruption
• Implement behavioral detection for processes attempting to access or manipulate assembly manifest parsing functions
• Deploy endpoint detection rules to identify known exploitation patterns targeting the SxS component
• Audit process creation events for unexpected privilege elevation from standard user to SYSTEM

Monitoring Recommendations

• Enable Windows Security Event logging for process creation (Event ID 4688) with command-line auditing
• Configure kernel audit policies to capture memory access violations and kernel exceptions
• Implement SIEM correlation rules to detect rapid privilege escalation patterns
• Monitor for anomalous file system activity in Windows SxS directories (%WINDIR%\WinSxS)

How to Mitigate CVE-2020-1027

Immediate Actions Required

• Apply Microsoft security patches immediately to all affected Windows systems
• Prioritize patching for systems in the CISA KEV catalog compliance requirements
• Isolate unpatched systems from network access where possible until patches can be applied
• Review privileged account usage and implement least-privilege access controls

Patch Information

Microsoft released security updates addressing CVE-2020-1027 as part of the April 2020 Patch Tuesday release. Organizations should apply the appropriate security update for their Windows version immediately. Detailed patch information and download links are available in the Microsoft Security Advisory for CVE-2020-1027.

The security update addresses the vulnerability by correcting how the Windows kernel handles objects in memory, implementing proper bounds checking in the affected XML parsing routines.

Workarounds

• Restrict local logon rights to trusted users only on critical systems
• Implement application whitelisting to prevent unauthorized code execution
• Enable Windows Defender Credential Guard on supported systems to limit credential theft impact
• Apply network segmentation to limit lateral movement opportunities for attackers who achieve local compromise

# Verify patch installation status using PowerShell
Get-HotFix | Where-Object {$_.HotFixID -match "KB453" -or $_.HotFixID -match "KB454"}

# Check Windows Update history for April 2020 security updates
wmic qfe list brief /format:table | findstr /i "2020-04"