CVE-2020-1349: Microsoft 365 Apps RCE Vulnerability

CVE-2020-1349 Overview

A remote code execution vulnerability exists in Microsoft Outlook software when it fails to properly handle objects in memory. This memory corruption flaw allows attackers to execute arbitrary code in the context of the current user by convincing a victim to open a specially crafted file or preview a malicious email message in Outlook.

Critical Impact

Successful exploitation enables attackers to execute arbitrary code with the privileges of the current user, potentially leading to complete system compromise, data theft, or malware installation.

Affected Products

• Microsoft 365 Apps for Enterprise
• Microsoft Office 2019
• Microsoft Outlook 2010 SP2, 2013 SP1, 2013 RT SP1, and 2016

Discovery Timeline

• 2020-07-14 - CVE-2020-1349 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-1349

Vulnerability Analysis

CVE-2020-1349 is a memory corruption vulnerability affecting Microsoft Outlook's handling of objects in memory. The vulnerability is classified as a Remote Code Execution (RCE) flaw, though it requires local user interaction to trigger. The attack scenario involves a user opening a specially crafted file or previewing a malicious email, making social engineering a key component of exploitation.

The vulnerability requires user interaction, meaning the attacker must convince the target to open or preview malicious content. Once triggered, the exploit can execute code with the same privileges as the logged-in user. If the user has administrative privileges, an attacker could gain full control over the affected system, install programs, view or modify data, or create new accounts with full user rights.

Root Cause

The root cause of this vulnerability lies in improper handling of objects in memory within the Microsoft Outlook application. When Outlook processes certain malformed objects, it fails to properly validate memory operations, creating an exploitable condition. This type of memory handling flaw is characteristic of vulnerabilities found in complex email client software that must parse various file formats and embedded objects.

Attack Vector

The attack vector for CVE-2020-1349 is local, requiring user interaction. An attacker would typically craft a malicious email with a specially formatted attachment or embed malicious objects directly in the email content. The exploitation can occur in several scenarios:

1. Preview Pane Attack: The user previews a malicious email in Outlook's preview pane
2. Attachment Opening: The user opens a crafted attachment sent via email
3. File Opening: The user opens a malicious file downloaded from another source

The vulnerability exploits the trust relationship users have with their email client, making phishing and social engineering critical components of a successful attack. Technical details and proof-of-concept exploit code have been published to security repositories, as documented in the Packet Storm RCE Exploit.

Detection Methods for CVE-2020-1349

Indicators of Compromise

• Unexpected OUTLOOK.EXE process spawning child processes or making unusual network connections
• Presence of suspicious email attachments with uncommon file extensions or malformed headers
• Unusual memory allocation patterns in Outlook application logs
• System event logs indicating crashes or exceptions in Microsoft Outlook prior to suspicious activity

Detection Strategies

• Monitor for abnormal child process creation from OUTLOOK.EXE, particularly command interpreters like cmd.exe or powershell.exe
• Implement email gateway filtering to scan attachments for known exploit signatures
• Deploy endpoint detection rules to identify memory corruption exploitation attempts in email clients
• Review application crash logs for repeated Outlook exceptions that may indicate exploitation attempts

Monitoring Recommendations

• Enable Windows Defender Exploit Guard protections for Microsoft Office applications
• Configure SIEM alerts for suspicious process chains originating from email client applications
• Monitor network traffic from Outlook processes for unexpected outbound connections
• Implement file integrity monitoring on Outlook-related system directories

How to Mitigate CVE-2020-1349

Immediate Actions Required

• Apply the Microsoft security update immediately to all affected systems
• Ensure Microsoft Outlook and Microsoft Office are updated to the latest patched versions
• Educate users about the risks of opening attachments or previewing emails from unknown senders
• Consider temporarily disabling the Outlook preview pane until patches are applied

Patch Information

Microsoft has released security updates to address this vulnerability. Affected organizations should apply the patches provided in the Microsoft Security Advisory CVE-2020-1349. The update addresses the memory handling issue by correcting how Microsoft Outlook processes objects in memory.

Ensure all instances of the following products are updated:

• Microsoft 365 Apps for Enterprise
• Microsoft Office 2019
• Microsoft Outlook 2010 SP2, 2013 SP1, 2013 RT SP1, and 2016

Workarounds

• Disable the Reading Pane in Microsoft Outlook to prevent automatic preview of malicious content
• Configure Outlook to download emails in plain text format instead of HTML
• Implement strict email filtering policies at the gateway level to block suspicious attachments
• Consider using Microsoft's Attack Surface Reduction rules to limit Office application behavior

# PowerShell: Enable Attack Surface Reduction rule to block Office apps from creating child processes
Set-MpPreference -AttackSurfaceReductionRules_Ids D4F940AB-401B-4EFC-AADC-AD5F3C50688A -AttackSurfaceReductionRules_Actions Enabled

# PowerShell: Configure Outlook to read emails in plain text (requires registry modification)
# Run in elevated PowerShell session
New-ItemProperty -Path "HKCU:\Software\Microsoft\Office\16.0\Outlook\Options\Mail" -Name "ReadAsPlain" -Value 1 -PropertyType DWORD -Force