CVE-2024-49027: Microsoft Excel RCE Vulnerability

CVE-2024-49027 Overview

CVE-2024-49027 is a remote code execution vulnerability in Microsoft Excel caused by a use-after-free condition [CWE-416]. An attacker who crafts a malicious Excel document can execute arbitrary code in the context of the current user when the target opens the file. The flaw affects multiple Microsoft Office variants, including Microsoft 365 Apps, Office 2016, Office 2019, and Office LTSC 2021 and 2024 on both Windows and macOS.

Microsoft published the advisory on November 12, 2024. The vulnerability requires user interaction and local access, but successful exploitation impacts confidentiality, integrity, and availability.

Critical Impact
Successful exploitation grants arbitrary code execution in the user's context, enabling attackers to install programs, view or modify data, and create new accounts with the same privileges as the logged-on user.

Affected Products

Microsoft 365 Apps for Enterprise
Microsoft Excel 2016, Microsoft Office 2019
Microsoft Office LTSC 2021 and 2024 (Windows and macOS)

Discovery Timeline

2024-11-12 - CVE-2024-49027 published to NVD
2024-11-12 - Microsoft releases security update for CVE-2024-49027
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-49027

Vulnerability Analysis

CVE-2024-49027 is a use-after-free vulnerability [CWE-416] in Microsoft Excel's document parsing logic. Excel frees a memory object during processing of a crafted spreadsheet but retains a dangling reference to that object. Subsequent operations dereference the freed pointer, allowing an attacker to influence control flow.

An attacker constructs a malicious .xlsx, .xls, or related Excel document containing structures that trigger the premature free and reuse pattern. When a user opens the file, Excel processes the embedded content, reaches the vulnerable code path, and reuses attacker-controlled data in place of the freed object.

Exploitation results in arbitrary code execution within the Excel process. The attacker inherits the privileges of the current user, which is sufficient for persistence, credential theft, and lateral movement in most enterprise environments.

Root Cause

The root cause is improper object lifetime management inside Excel's file parsing routines. Excel releases an internal object during handling of specially crafted spreadsheet elements but continues to hold a reference to the freed memory. Reuse of that stale pointer permits controlled memory corruption.

Attack Vector

The attack requires local access with user interaction. An attacker delivers the malicious Excel file through phishing, a compromised web download, or a shared network location. The victim must open the document in a vulnerable version of Excel for the exploit to execute. The Preview Pane is not a documented attack vector for this CVE.

The vulnerability manifests during Excel's parsing of crafted document structures. See the Microsoft Security Update CVE-2024-49027 advisory for vendor-supplied technical details.

Detection Methods for CVE-2024-49027

Indicators of Compromise

Excel process (EXCEL.EXE) spawning unusual child processes such as cmd.exe, powershell.exe, wscript.exe, or rundll32.exe
Excel process making outbound network connections to unrecognized domains shortly after opening a document
Unexpected writes to %APPDATA%, %TEMP%, or Startup folders originating from EXCEL.EXE
Crash dumps for EXCEL.EXE referencing heap corruption or access violations during document open

Detection Strategies

Hunt for child-process anomalies where Office applications spawn script interpreters or LOLBins
Correlate email gateway telemetry with endpoint file-open events for Excel documents sourced externally
Apply YARA rules targeting known malicious spreadsheet structures and OLE stream anomalies
Alert on Excel-initiated persistence artifacts including Run key modifications and scheduled task creation

Monitoring Recommendations

Enable Microsoft Defender Attack Surface Reduction rules that block Office child-process creation
Ingest Sysmon Event IDs 1 (process create), 3 (network), and 11 (file create) for Office binaries into your SIEM
Baseline normal Excel behavior per business unit to reduce false positives on macro-heavy workflows
Track document provenance via Mark-of-the-Web (MOTW) and Zone.Identifier alternate data streams

How to Mitigate CVE-2024-49027

Immediate Actions Required

Apply the November 2024 Microsoft security updates to all affected Excel and Office installations without delay
Verify patch deployment across Microsoft 365 Apps, Office 2016, Office 2019, and Office LTSC 2021 and 2024 on Windows and macOS
Enforce Protected View and Block Macros From The Internet policies for Office documents originating outside the organization
Prioritize patching for users who routinely receive external spreadsheets, such as finance and procurement teams

Patch Information

Microsoft released fixes concurrent with the November 12, 2024 disclosure. Refer to the Microsoft Security Update CVE-2024-49027 advisory for the specific build numbers per channel and platform. Microsoft 365 Apps receives updates through the standard Click-to-Run channel; volume-licensed Office 2016/2019 and LTSC editions require the corresponding security update packages.

Workarounds

Configure Excel to open documents from the internet in Protected View and disable trust for network locations
Use Group Policy or Intune to block Excel from creating child processes via Attack Surface Reduction rules
Restrict opening of Excel attachments at the email gateway when patches cannot be applied immediately
Educate users to avoid opening unsolicited spreadsheet files, particularly those requesting content activation

bash

# Example: Enable ASR rule to block Office apps from creating child processes (PowerShell)
Add-MpPreference -AttackSurfaceReductionRules_Ids D4F940AB-401B-4EFC-AADC-AD5F3C50688A `
                 -AttackSurfaceReductionRules_Actions Enabled