CVE-2023-28285: Microsoft 365 Apps RCE Vulnerability

CVE-2023-28285 Overview

CVE-2023-28285 is a Remote Code Execution vulnerability affecting Microsoft Office products, including Microsoft 365 Apps and Office Long Term Servicing Channel editions. This vulnerability allows an attacker to execute arbitrary code on the target system when a user opens a specially crafted file. The attack requires user interaction, making it a prime candidate for social engineering attacks through malicious documents delivered via email or other means.

Critical Impact

Successful exploitation of this vulnerability allows attackers to execute arbitrary code with the privileges of the current user, potentially leading to complete system compromise, data exfiltration, or lateral movement within enterprise networks.

Affected Products

• Microsoft 365 Apps for Enterprise
• Microsoft Office 2019 for macOS
• Microsoft Office Long Term Servicing Channel 2021 for macOS

Discovery Timeline

• April 11, 2023 - CVE-2023-28285 published to NVD
• January 1, 2025 - Last updated in NVD database

Technical Details for CVE-2023-28285

Vulnerability Analysis

CVE-2023-28285 is classified under CWE-416 (Use After Free), a memory corruption vulnerability that occurs when a program continues to use a pointer after it has been freed. In the context of Microsoft Office, this vulnerability is triggered when processing specially crafted documents. The exploitation requires local access, meaning an attacker must convince a user to open a malicious document file.

The vulnerability exists in the document parsing functionality of Microsoft Office applications. When a user opens a maliciously crafted document, the application improperly handles certain objects in memory. This leads to a use-after-free condition where the application references memory that has already been deallocated, allowing an attacker to potentially control the execution flow and execute arbitrary code.

Root Cause

The root cause of this vulnerability is a Use After Free (CWE-416) memory management error in Microsoft Office's document processing code. The application fails to properly track and validate object lifetimes during document parsing operations. When processing certain document elements, the code frees a memory object but retains a dangling pointer that can be subsequently dereferenced. An attacker can craft a document that manipulates the heap layout to control the freed memory region, enabling arbitrary code execution when the dangling pointer is accessed.

Attack Vector

The attack vector for CVE-2023-28285 is local, requiring user interaction to execute. The typical attack scenario involves:

1. An attacker crafts a malicious Office document (such as .docx, .xlsx, or .pptx) that triggers the use-after-free condition
2. The document is delivered to the victim through phishing emails, malicious websites, or file-sharing services
3. When the victim opens the document with a vulnerable version of Microsoft Office, the exploit triggers
4. The attacker gains code execution in the context of the user's session

The vulnerability is particularly concerning in enterprise environments where document sharing is common. Attackers may leverage this vulnerability as an initial access vector, combining it with social engineering tactics to trick users into opening malicious attachments.

Technical details and proof-of-concept information have been documented in security research. For further technical analysis, see the Packet Storm Security advisory and the Microsoft 365 MSO specific disclosure.

Detection Methods for CVE-2023-28285

Indicators of Compromise

• Suspicious Microsoft Office document files with unusual embedded objects or macros received via email or downloaded from untrusted sources
• Unexpected child processes spawned by Office applications (WINWORD.EXE, EXCEL.EXE, POWERPNT.EXE)
• Memory allocation anomalies or crash dumps from Office processes indicating heap corruption
• Network connections initiated by Office processes to external or suspicious IP addresses

Detection Strategies

• Monitor for Office applications spawning unusual child processes such as cmd.exe, powershell.exe, or mshta.exe
• Implement endpoint detection rules that alert on Office process behaviors consistent with exploitation (e.g., process injection, credential access attempts)
• Deploy YARA rules to scan incoming documents for known exploitation patterns associated with CVE-2023-28285
• Utilize SentinelOne's behavioral AI engine to detect anomalous Office application behavior indicative of memory corruption exploits

Monitoring Recommendations

• Enable detailed logging for Microsoft Office applications and Windows Event Logs to capture process creation events
• Configure email security gateways to scan and sandbox incoming Office documents before delivery to end users
• Deploy network monitoring to detect post-exploitation communication patterns from compromised endpoints
• Implement file integrity monitoring on critical systems to detect unauthorized changes following potential exploitation

How to Mitigate CVE-2023-28285

Immediate Actions Required

• Apply the latest security updates from Microsoft for all affected Office products immediately
• Ensure automatic updates are enabled for Microsoft 365 Apps to receive future security patches
• Educate users about the risks of opening documents from untrusted sources
• Consider implementing application whitelisting to prevent unauthorized code execution

Patch Information

Microsoft has released security updates to address CVE-2023-28285. Organizations should apply the patches available through the Microsoft Security Update Guide for CVE-2023-28285. For Microsoft 365 Apps Enterprise, ensure the application is updated to the latest build. For Office 2019 and Office LTSC 2021 on macOS, apply the latest cumulative updates provided by Microsoft through the standard update mechanisms.

Workarounds

• Block Office documents from untrusted sources at the email gateway level using attachment filtering policies
• Enable Protected View for Office documents to open files from the internet in a restricted mode by default
• Disable unnecessary Office features such as macros and embedded objects until patches can be applied
• Implement network segmentation to limit the impact of potential exploitation on critical systems

Organizations using SentinelOne can leverage the platform's behavioral detection capabilities to identify and block exploitation attempts targeting this vulnerability, providing an additional layer of protection while patching is in progress.