CVE-2025-62201: Microsoft 365 Apps Buffer Overflow Flaw

CVE-2025-62201 Overview

CVE-2025-62201 is a heap-based buffer overflow vulnerability in Microsoft Office Excel that enables local code execution. The flaw is tracked under CWE-122 and affects multiple Microsoft Office products including Microsoft 365 Apps, Excel 2016, Office 2019, Office LTSC 2021, Office LTSC 2024, and Office Online Server. Exploitation requires user interaction, typically by opening a crafted Excel document. Successful exploitation grants the attacker the ability to run arbitrary code in the context of the current user, compromising confidentiality, integrity, and availability.

Critical Impact

An attacker who convinces a user to open a malicious Excel file can execute code on the local system with that user's privileges, leading to data theft, persistence, or lateral movement.

Affected Products

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

Discovery Timeline

• 2025-11-11 - CVE-2025-62201 published to NVD
• 2025-11-11 - Microsoft releases security update guidance for CVE-2025-62201
• 2025-11-17 - Last updated in NVD database

Technical Details for CVE-2025-62201

Vulnerability Analysis

The vulnerability is a heap-based buffer overflow in Microsoft Office Excel's document parsing logic. When Excel processes a specifically crafted workbook, a length or size value is not validated against the destination buffer allocated on the heap. The parser writes attacker-controlled data beyond the bounds of that buffer, corrupting adjacent heap metadata or object pointers. An attacker who shapes the heap layout in advance can convert this corruption into control-flow hijacking and execute code in the context of the user running Excel.

Because the attack vector is local and requires user interaction, the typical delivery method is a malicious .xlsx, .xls, or .xlsm file sent via email, hosted on a website, or delivered through a file share. Preview pane processing may also trigger the parsing path. Code executes with the privileges of the victim, which on workstations is often a standard or local administrator account.

Root Cause

The root cause is improper validation of input-driven size or length fields during heap buffer allocation and population. Insufficient bounds checking in the Excel file parser allows attacker-controlled data to exceed the allocated heap region, which is the classic pattern described by CWE-122: Heap-based Buffer Overflow.

Attack Vector

An attacker crafts a malicious Excel document containing the trigger structure and delivers it via phishing, drive-by download, or shared storage. When the victim opens the document — or in some cases previews it — the malformed object is parsed, the heap is corrupted, and the attacker's payload executes locally. No network authentication is required, and the attacker needs no prior access to the target system. Microsoft has not reported in-the-wild exploitation, and the CVE is not currently listed in the CISA Known Exploited Vulnerabilities catalog.

No public proof-of-concept exploit is available at this time. See the Microsoft Security Update Guide for CVE-2025-62201 for vendor technical details.

Detection Methods for CVE-2025-62201

Indicators of Compromise

• Unexpected child processes spawned by EXCEL.EXE, such as cmd.exe, powershell.exe, rundll32.exe, regsvr32.exe, or mshta.exe.
• Crashes or Windows Error Reporting events referencing EXCEL.EXE shortly after a user opens an attachment.
• Office documents written to disk from email clients or browsers, followed by outbound network connections from Excel.
• New persistence artifacts (Run keys, Scheduled Tasks, startup files) created in the user profile after opening a workbook.

Detection Strategies

• Hunt for process-lineage anomalies where EXCEL.EXE is the parent of script interpreters, LOLBins, or download utilities.
• Inspect inbound email attachments and shared workbooks for malformed BIFF records, OLE streams, or oversized embedded objects.
• Correlate Excel crash telemetry with subsequent file-write or network activity to surface post-exploitation behavior.

Monitoring Recommendations

• Enable and forward Sysmon process-creation, image-load, and network-connection events from endpoints running Microsoft Office.
• Monitor Microsoft Defender Application Guard for Office events and ASR (Attack Surface Reduction) rule triggers related to Office child processes.
• Alert on Office processes loading non-standard DLLs or making outbound connections to uncategorized destinations.

How to Mitigate CVE-2025-62201

Immediate Actions Required

• Apply the Microsoft security update for CVE-2025-62201 referenced in the MSRC advisory to all affected Office installations.
• Prioritize patching endpoints used by high-risk roles, including finance, executive assistants, and any user who routinely opens external workbooks.
• Verify update status across Microsoft 365 Apps, Office 2016/2019, and Office LTSC 2021/2024 fleets, including macOS builds.

Patch Information

Microsoft has issued security updates through the standard Microsoft 365 Apps update channels and the Microsoft Update Catalog. Refer to the Microsoft Security Update Guide for CVE-2025-62201 for the specific build numbers, KB identifiers, and macOS package versions that contain the fix.

Workarounds

• Enable Protected View and Office Protected View for files originating from the internet, email attachments, and unsafe locations.
• Configure Attack Surface Reduction rules to block Office applications from creating child processes and from injecting code into other processes.
• Disable the Outlook preview pane and Windows Explorer preview handler for Office documents until patching is complete.
• Restrict execution of macros from the internet via Group Policy and enforce signed-macro requirements for trusted workflows.

# Example: enforce key Attack Surface Reduction rules via PowerShell
# Block Office applications from creating child processes
Set-MpPreference -AttackSurfaceReductionRules_Ids D4F940AB-401B-4EFC-AADC-AD5F3C50688A `
                 -AttackSurfaceReductionRules_Actions Enabled

# Block Office applications from injecting code into other processes
Set-MpPreference -AttackSurfaceReductionRules_Ids 75668C1F-73B5-4CF0-BB93-3ECF5CB7CC84 `
                 -AttackSurfaceReductionRules_Actions Enabled

# Block Win32 API calls from Office macros
Set-MpPreference -AttackSurfaceReductionRules_Ids 92E97FA1-2EDF-4476-BDD6-9DD0B4DDDC7B `
                 -AttackSurfaceReductionRules_Actions Enabled