CVE-2021-31979: Windows 10 1507 Privilege Escalation Flaw

CVE-2021-31979 Overview

CVE-2021-31979 is a Windows Kernel Elevation of Privilege vulnerability that affects a wide range of Microsoft Windows operating systems. This vulnerability exists in the Windows kernel and allows a local attacker with low privileges to escalate their permissions to SYSTEM level, gaining complete control over the affected system. The vulnerability has been confirmed as actively exploited in the wild and is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, making immediate remediation critical for all affected organizations.

Critical Impact

This kernel-level privilege escalation vulnerability is actively exploited in the wild and listed in CISA's KEV catalog, enabling attackers to gain SYSTEM privileges and full control of affected Windows systems.

Affected Products

• Microsoft Windows 10 (versions 1507, 1607, 1809, 1909, 2004, 20H2, 21H1)
• Microsoft Windows 7 SP1
• Microsoft Windows 8.1 and Windows RT 8.1
• Microsoft Windows Server 2008 SP2 and R2 SP1
• Microsoft Windows Server 2012 and 2012 R2
• Microsoft Windows Server 2016, 2019, 2004, and 20H2

Discovery Timeline

• July 14, 2021 - CVE-2021-31979 published to NVD
• October 29, 2025 - Last updated in NVD database

Technical Details for CVE-2021-31979

Vulnerability Analysis

CVE-2021-31979 is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), indicating that the vulnerability stems from improper memory handling within the Windows kernel. This type of flaw typically occurs when kernel code fails to properly validate or restrict memory operations, allowing an attacker to manipulate memory in unintended ways.

The vulnerability requires local access to the target system and low privileges to exploit, meaning an attacker who has gained initial access through another means (such as phishing or a separate vulnerability) can leverage this flaw to escalate from a standard user to SYSTEM-level privileges. Once elevated, the attacker would have unrestricted access to the system, including the ability to install programs, view or modify any data, create accounts with full privileges, and disable security software.

Root Cause

The root cause of this vulnerability lies in improper boundary checking within Windows kernel memory operations. The CWE-119 classification indicates that the kernel fails to properly restrict operations within memory buffer bounds, allowing for potential buffer overflows or out-of-bounds access. This memory corruption vulnerability in kernel-mode code is particularly dangerous as it operates at the highest privilege level of the operating system.

Attack Vector

The attack vector for CVE-2021-31979 is local, requiring the attacker to execute code on the target system. A threat actor would typically:

1. Gain initial access to the target system through social engineering, exploitation of a different vulnerability, or compromised credentials
2. Execute a specially crafted application or code that triggers the kernel vulnerability
3. Manipulate kernel memory through the improper bounds checking flaw
4. Achieve privilege escalation from a low-privileged user to SYSTEM level
5. Maintain persistence and move laterally within the network with elevated privileges

The vulnerability's active exploitation in the wild, as documented by CISA's KEV listing, demonstrates that threat actors are successfully incorporating this vulnerability into their attack chains.

Detection Methods for CVE-2021-31979

Indicators of Compromise

• Suspicious processes running with elevated SYSTEM privileges that originated from user-level processes
• Abnormal kernel memory access patterns or crashes related to ntoskrnl.exe
• Unexpected privilege token modifications in Windows Security Event logs
• Process creation events showing unusual parent-child relationships with privilege escalation

Detection Strategies

• Monitor Windows Security Event ID 4688 (Process Creation) for suspicious privilege escalation patterns
• Implement kernel integrity monitoring to detect unauthorized kernel memory modifications
• Deploy endpoint detection rules that identify known exploitation techniques for privilege escalation
• Utilize SentinelOne's behavioral AI engine to detect anomalous privilege escalation attempts

Monitoring Recommendations

• Enable Windows Event Log auditing for Process Creation, Token Manipulation, and Privilege Use categories
• Configure SIEM rules to alert on rapid privilege escalation sequences from low-privilege accounts
• Monitor for unusual SYSTEM-level process spawning from user-space applications
• Implement real-time kernel monitoring solutions to detect exploitation attempts

How to Mitigate CVE-2021-31979

Immediate Actions Required

• Apply the July 2021 Microsoft security updates immediately to all affected Windows systems
• Prioritize patching of internet-facing and critical infrastructure systems first
• Implement network segmentation to limit lateral movement opportunities for attackers
• Review systems for signs of compromise, as this vulnerability has been actively exploited

Patch Information

Microsoft released security patches for CVE-2021-31979 as part of the July 2021 Patch Tuesday updates. Organizations should obtain patches from the Microsoft Security Advisory for CVE-2021-31979. Given the vulnerability's presence in the CISA Known Exploited Vulnerabilities Catalog, federal agencies and critical infrastructure organizations may have mandatory remediation deadlines.

Workarounds

• Restrict local logon access to trusted users only, minimizing the attack surface for local privilege escalation
• Implement application whitelisting to prevent unauthorized code execution that could trigger the exploit
• Enable Credential Guard and other Windows virtualization-based security features where supported
• Deploy endpoint protection solutions with behavioral analysis capabilities to detect exploitation attempts

# Verify Windows Update installation status for KB articles addressing CVE-2021-31979
wmic qfe list full | findstr /i "KB5004237 KB5004245 KB5004244"

# Check current Windows kernel version
ver
systeminfo | findstr /B /C:"OS Version"