CVE-2021-31945: Microsoft Paint 3D RCE Vulnerability

CVE-2021-31945 Overview

CVE-2021-31945 is a remote code execution vulnerability affecting Microsoft Paint 3D. This vulnerability allows attackers to execute arbitrary code on target systems through maliciously crafted files processed by the Paint 3D application. The vulnerability requires user interaction, as victims must open a specially crafted file to trigger the exploit.

Critical Impact

Successful exploitation of this vulnerability could allow an attacker to execute arbitrary code with the privileges of the current user, potentially leading to high confidentiality impact with limited integrity and availability impact.

Affected Products

• Microsoft Paint 3D (all versions prior to patch)

Discovery Timeline

• 2021-06-08 - CVE CVE-2021-31945 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-31945

Vulnerability Analysis

This remote code execution vulnerability exists within Microsoft Paint 3D, a 3D modeling and design application included with Windows 10. The vulnerability is classified under "NVD-CWE-noinfo," indicating the specific weakness type has not been disclosed by the vendor.

Based on the Zero Day Initiative Advisory ZDI-21-667, this vulnerability was identified through coordinated disclosure. The local attack vector combined with the requirement for user interaction suggests this is likely a file parsing vulnerability that triggers when Paint 3D processes a maliciously crafted 3D model file or project file.

The vulnerability presents a high confidentiality impact, meaning successful exploitation could result in significant information disclosure from the affected system. The limited integrity and availability impacts suggest the exploit may not provide complete system control but could still result in data exfiltration or modification of user files.

Root Cause

While Microsoft has not disclosed the specific technical root cause (classified as NVD-CWE-noinfo), the characteristics of this vulnerability suggest a potential memory corruption or improper input validation issue within Paint 3D's file parsing routines. The application processes complex 3D file formats that may contain embedded objects, textures, and metadata, any of which could serve as attack vectors if improperly validated.

Attack Vector

The attack vector for CVE-2021-31945 is local, requiring an attacker to convince a user to open a maliciously crafted file with Paint 3D. Common attack scenarios include:

The attacker delivers a malicious 3D model file (such as .3mf, .fbx, .obj, or other supported formats) through phishing emails, malicious websites, or compromised file sharing services. When the victim opens this file with Paint 3D, the vulnerability is triggered, potentially allowing arbitrary code execution in the context of the current user.

No public proof-of-concept exploit code is currently available for this vulnerability. For technical details, refer to the Microsoft Security Advisory CVE-2021-31945.

Detection Methods for CVE-2021-31945

Indicators of Compromise

• Unusual child processes spawned by PaintStudio.View.exe (Paint 3D executable)
• Unexpected network connections initiated by the Paint 3D process
• Presence of suspicious 3D model files in user download directories or email attachments
• Memory access violations or crash dumps related to Paint 3D

Detection Strategies

• Monitor process creation events for PaintStudio.View.exe spawning unexpected child processes such as cmd.exe, powershell.exe, or script interpreters
• Implement file integrity monitoring to detect modification of Paint 3D application files
• Deploy endpoint detection rules to identify suspicious behavior patterns following Paint 3D file operations
• Analyze Windows Event Logs for application crashes or errors related to Paint 3D

Monitoring Recommendations

• Enable Windows Defender Application Guard or similar isolation technologies for opening untrusted files
• Configure endpoint security solutions to monitor Paint 3D process behavior and network activity
• Implement email security scanning to detect potentially malicious 3D model file attachments
• Review application crash telemetry for patterns indicating exploitation attempts

How to Mitigate CVE-2021-31945

Immediate Actions Required

• Apply the latest security updates for Microsoft Paint 3D through the Microsoft Store
• Educate users about the risks of opening 3D model files from untrusted sources
• Consider temporarily restricting Paint 3D usage until patches are applied
• Implement application whitelisting to control which applications can execute on endpoints

Patch Information

Microsoft has released a security update to address this vulnerability. The patch is distributed through the Microsoft Store for Paint 3D. Administrators should ensure that automatic updates are enabled for Microsoft Store applications, or manually update Paint 3D through the Store interface.

For detailed patch information and guidance, refer to the Microsoft Security Advisory CVE-2021-31945.

Workarounds

• Uninstall Paint 3D if it is not required for business operations
• Block potentially malicious 3D file types (.3mf, .fbx, .obj, .stl, .ply, .glb, .gltf) at email and web gateways
• Run Paint 3D in a sandboxed or virtualized environment when processing untrusted files
• Configure Windows Defender Exploit Protection settings for the Paint 3D application

# PowerShell: Uninstall Paint 3D if not needed
Get-AppxPackage *Microsoft.MSPaint* | Remove-AppxPackage

# Block Paint 3D from executing untrusted files using AppLocker or WDAC policies