CVE-2025-62203: Microsoft 365 Apps Use-After-Free Flaw

CVE-2025-62203 Overview

CVE-2025-62203 is a use-after-free vulnerability in Microsoft Office Excel that allows an unauthorized attacker to execute code locally. The flaw affects multiple supported Office releases, including Microsoft 365 Apps, Excel 2016, Office 2019, Office LTSC 2021, Office LTSC 2024, and Office Online Server. Exploitation requires a user to open a crafted Excel document, after which arbitrary code runs in the context of the current user. Microsoft published the advisory on November 11, 2025, and the entry was last updated in the National Vulnerability Database on November 17, 2025.

Critical Impact
A successful attack yields high impact to confidentiality, integrity, and availability on the affected host, enabling code execution under the logged-on user's privileges.

Affected Products

Microsoft 365 Apps (Enterprise, x64 and x86)
Microsoft Excel 2016, Microsoft Office 2019
Microsoft Office LTSC 2021, Office LTSC 2024, and Office Online Server

Discovery Timeline

2025-11-11 - Microsoft publishes advisory for CVE-2025-62203
2025-11-11 - CVE-2025-62203 published to NVD
2025-11-17 - Last updated in NVD database

Technical Details for CVE-2025-62203

Vulnerability Analysis

The issue is classified as a use-after-free condition [CWE-416] in Microsoft Office Excel. Use-after-free defects occur when code continues to reference a memory region after it has been released, allowing an attacker to influence the contents of that memory before it is reused. In Excel, parsing of crafted spreadsheet structures can leave dangling pointers that the application later dereferences during rendering or recalculation. An attacker who controls the freed allocation can substitute attacker-shaped data, redirect execution flow, and achieve local code execution under the user's account.

Root Cause

The root cause is improper object lifetime management within Excel's document-handling code. Specific components free an internal object while other code paths retain references to it. When those references are later used, Excel operates on memory that may have been reclaimed and overwritten by attacker-controlled content embedded in a crafted XLS, XLSX, or related Office document. CWE-416 issues of this type are a common precursor to control-flow hijacking through corrupted virtual table pointers or function pointers.

Attack Vector

The attack vector is local and requires user interaction. The adversary delivers a malicious Excel file through email, web download, or a shared location and persuades the target to open it. No network access to the host is required, and the attacker does not need prior privileges. Code executes with the same rights as the user opening the document, which on workstations is typically a standard or administrative interactive account.

No public proof-of-concept code or verified exploit samples are available for this CVE at the time of writing. Refer to the Microsoft CVE-2025-62203 Advisory for vendor-supplied technical context.

Detection Methods for CVE-2025-62203

Indicators of Compromise

Excel processes (EXCEL.EXE) spawning unexpected child processes such as cmd.exe, powershell.exe, rundll32.exe, mshta.exe, or wscript.exe.
Crash dumps or Windows Error Reporting events tied to EXCEL.EXE following the opening of an Office document received from external sources.
Office documents originating from email or web downloads that contain unusual embedded objects, ActiveX controls, or malformed structured storage streams.

Detection Strategies

Hunt for parent-child process relationships where Microsoft Office binaries launch script interpreters or living-off-the-land binaries.
Alert on Office applications writing executable content (.exe, .dll, .js, .hta) to user-writable directories such as %TEMP%, %APPDATA%, or %PUBLIC%.
Inspect inbound mail attachments and downloaded files for Excel documents flagged with Mark-of-the-Web that contain suspicious OLE or embedded objects.

Monitoring Recommendations

Enable Microsoft Defender Attack Surface Reduction rules that block Office applications from creating child processes and from injecting code into other processes.
Forward Sysmon process, image-load, and file-create events from endpoints running Office to a centralized analytics platform for retrospective hunting.
Track Office telemetry for repeated crashes of EXCEL.EXE across multiple users, which can indicate active exploitation attempts.

How to Mitigate CVE-2025-62203

Immediate Actions Required

Apply the November 2025 Microsoft security updates for all affected Office and Microsoft 365 Apps channels as documented in the vendor advisory.
Prioritize patching for users who routinely process Excel files from external senders, including finance, procurement, and executive assistants.
Confirm that Microsoft 365 Apps update channels are not paused and that managed devices have received the corresponding build.

Patch Information

Microsoft has released security updates that remediate this vulnerability across the affected products. Administrators should consult the Microsoft CVE-2025-62203 Advisory for the exact build numbers and KB articles applicable to each channel, including Microsoft 365 Apps, Excel 2016, Office 2019, Office LTSC 2021, Office LTSC 2024, and Office Online Server.

Workarounds

Open untrusted Excel files only in Protected View and keep the Block macros from running in Office files from the Internet policy enabled.
Configure File Block policies to prevent legacy Excel binary formats from opening or to force them through Protected View.
Restrict end users from running Excel with administrative privileges to limit the impact of successful exploitation.

bash

# Example Group Policy registry settings to enforce Protected View for Excel files from the Internet and from unsafe locations
reg add "HKCU\Software\Microsoft\Office\16.0\Excel\Security\ProtectedView" /v DisableInternetFilesInPV /t REG_DWORD /d 0 /f
reg add "HKCU\Software\Microsoft\Office\16.0\Excel\Security\ProtectedView" /v DisableUnsafeLocationsInPV /t REG_DWORD /d 0 /f
reg add "HKCU\Software\Microsoft\Office\16.0\Excel\Security\ProtectedView" /v DisableAttachmentsInPV /t REG_DWORD /d 0 /f