CVE-2021-38650: Microsoft 365 Apps Spoofing Vulnerability

CVE-2021-38650 Overview

CVE-2021-38650 is a spoofing vulnerability affecting multiple versions of Microsoft Office and Microsoft 365 Apps. This vulnerability enables an attacker to manipulate how content is displayed or interpreted within Office applications, potentially deceiving users into trusting malicious content. While classified as low severity, the spoofing nature of this vulnerability could be leveraged in targeted phishing or social engineering campaigns.

Critical Impact

Attackers can exploit this spoofing vulnerability to deceive users by manipulating how content appears within Microsoft Office applications, potentially facilitating social engineering attacks.

Affected Products

• Microsoft 365 Apps Enterprise
• Microsoft Office 2013 SP1
• Microsoft Office 2016
• Microsoft Office 2019 (Windows and macOS)

Discovery Timeline

• September 15, 2021 - CVE-2021-38650 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2021-38650

Vulnerability Analysis

This spoofing vulnerability in Microsoft Office allows an authenticated attacker to manipulate how content is presented to users. The attack requires user interaction, meaning a victim must open a specially crafted document or interact with malicious content for exploitation to succeed. The vulnerability affects the integrity of displayed information without impacting confidentiality or availability of the system.

The attack can be initiated over a network, requiring the attacker to have low-level privileges on the target system. The successful exploitation results in a low integrity impact, enabling the attacker to modify how information appears to the user, which could be used to support broader social engineering campaigns.

Root Cause

The vulnerability stems from improper handling of content rendering within Microsoft Office applications. The specific weakness has not been categorized under a standard CWE classification (NVD-CWE-noinfo), but the spoofing nature indicates issues with content validation or display mechanisms that allow malicious actors to present false or misleading information to users.

Attack Vector

The attack requires the following conditions:

1. The attacker must be authenticated with low-level privileges
2. User interaction is required (victim must open or interact with malicious content)
3. The attack can be executed over a network connection
4. The attacker crafts a malicious Office document that exploits the spoofing vulnerability
5. When the victim opens the document, content is displayed in a misleading manner that could support phishing or social engineering attacks

Due to the nature of this vulnerability, exploitation typically involves social engineering to convince a user to open a malicious document.

Detection Methods for CVE-2021-38650

Indicators of Compromise

• Unusual Office documents received from unknown or untrusted sources
• Office documents with unexpected content rendering behavior
• Reports from users about document content appearing differently than expected
• Documents that prompt users to take actions based on misleading displayed information

Detection Strategies

• Monitor for Office documents with suspicious properties or metadata anomalies
• Implement email security controls to scan attachments for known malicious patterns
• Deploy endpoint detection solutions that can identify exploitation attempts against Office applications
• Enable Microsoft Defender for Office 365 to detect malicious document attachments

Monitoring Recommendations

• Enable enhanced logging for Office application activity
• Monitor network traffic for downloads of Office documents from suspicious sources
• Track user reports of unusual document behavior as potential early indicators
• Review security alerts from endpoint protection solutions for Office-related anomalies

How to Mitigate CVE-2021-38650

Immediate Actions Required

• Apply the latest security updates from Microsoft for all affected Office products
• Update Microsoft 365 Apps to the latest available version
• Educate users about the risks of opening documents from untrusted sources
• Enable Protected View settings in Microsoft Office applications

Patch Information

Microsoft has released security patches addressing this vulnerability. Detailed patch information is available through the Microsoft Security Advisory CVE-2021-38650. Organizations should prioritize updating the following products:

• Microsoft 365 Apps Enterprise
• Microsoft Office 2013 SP1
• Microsoft Office 2016
• Microsoft Office 2019 (Windows and macOS)

Workarounds

• Enable Protected View for files originating from the Internet in Office Trust Center settings
• Configure Office applications to open documents from untrusted locations in Protected View
• Implement application whitelisting to prevent execution of malicious macros
• Train users to verify document authenticity through out-of-band communication when content appears suspicious

# Enable Protected View via Group Policy
# Navigate to: User Configuration > Administrative Templates > Microsoft Office > Security Settings > Trust Center
# Enable: "Open files from the Internet in Protected View"
# Enable: "Open files in potentially unsafe locations in Protected View"