CVE-2026-97768: Microsoft Excel Buffer Overflow Vulnerability

CVE-2026-97768 Overview

CVE-2026-97768 is a heap-based buffer overflow vulnerability [CWE-122] in Microsoft Office Excel. An unauthorized attacker can execute arbitrary code over a network by convincing a user to open a crafted Excel document. The flaw carries a CVSS 3.1 base score of 8.8 and requires user interaction to trigger. Successful exploitation yields high impact to confidentiality, integrity, and availability within the context of the current user.

Critical Impact
Remote attackers can execute arbitrary code on target systems when a user opens a malicious Excel file, potentially leading to full compromise of the user's session and lateral movement within enterprise environments.

Affected Products

Microsoft Office Excel (see Microsoft Security Update Guide for specific build and channel coverage)
Microsoft 365 Apps distributions of Excel as listed in the Microsoft advisory
Standalone Microsoft Office installations of Excel as listed in the Microsoft advisory

Discovery Timeline

2026-10-13 - CVE-2026-97768 published to the National Vulnerability Database (NVD)
2026-10-13 - Last updated in NVD database

Technical Details for CVE-2026-97768

Vulnerability Analysis

The vulnerability is a heap-based buffer overflow in Microsoft Office Excel. Excel allocates a buffer on the heap when parsing structured data within a spreadsheet file. The parser writes beyond the allocated bounds when processing crafted record fields, corrupting adjacent heap metadata and application objects. Attackers can shape the heap layout to overwrite function pointers or virtual table entries referenced during subsequent operations.

Exploitation redirects execution to attacker-controlled code within the Excel process. The resulting code runs with the privileges of the user who opened the document. In enterprise environments, this often grants access to user credentials, mapped shares, and local data. Attackers can chain this foothold with privilege escalation or credential theft techniques to expand access.

Root Cause

The root cause is improper validation of input size prior to a heap write operation inside Excel's file parsing logic. Excel does not confirm that user-supplied record lengths fit within the destination buffer. This classifies the issue under [CWE-122] Heap-based Buffer Overflow. Microsoft has not published the specific parser component in public documentation.

Attack Vector

The attack vector is Network with low attack complexity and no required privileges, but user interaction is required. A typical attack scenario delivers a weaponized .xlsx, .xls, or .xlsb file through email, cloud storage links, or a compromised web resource. When the victim opens the file, Excel parses the malicious record and triggers the overflow. Preview Pane rendering may expand the exposure surface depending on the installed version and configuration.

No verified public exploit code is available at the time of publication. Refer to the Microsoft Security Update Guide for authoritative technical references.

Detection Methods for CVE-2026-97768

Indicators of Compromise

Unexpected child processes spawned by EXCEL.EXE, such as cmd.exe, powershell.exe, rundll32.exe, or mshta.exe.
Excel initiating outbound network connections to uncommon domains or IP addresses shortly after a document is opened.
Creation of executable files, scripts, or scheduled tasks by the Excel process in user-writable directories such as %APPDATA% or %TEMP%.
Crash events or Windows Error Reporting entries referencing EXCEL.EXE with access violations in heap-related modules.

Detection Strategies

Hunt for process lineage anomalies where EXCEL.EXE is the parent of interpreters, LOLBins, or signed binaries used for proxy execution.
Inspect Office documents received via email for malformed records, embedded objects, or unusually large binary structures.
Correlate document open events with subsequent file writes, registry modifications, and network beaconing patterns.
Deploy YARA rules that identify crafted Excel structures referenced by vendor and community research as parsing exploits emerge.

Monitoring Recommendations

Centralize Microsoft Office telemetry, Sysmon events, and EDR process data for cross-source correlation.
Alert on Office applications loading unexpected DLLs or injecting code into other processes.
Monitor email gateways for spreadsheets originating from external senders with macros, external links, or embedded OLE objects.

How to Mitigate CVE-2026-97768

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft Security Update Guide to all affected Excel installations.
Prioritize patch deployment for workstations handling untrusted documents, including executive assistants, finance, HR, and support teams.
Validate that Microsoft 365 Apps update channels are current and that offline or air-gapped systems receive patches through managed deployment.
Block inbound Excel attachments from untrusted external senders at the email gateway until patching is confirmed.

Patch Information

Microsoft has published fixes through its regular security update process. Review the Microsoft Security Update Guide entry for CVE-2026-97768 for the exact KB numbers, affected build ranges, and channel-specific guidance. Enterprises managing Office through Microsoft Intune, Configuration Manager, or WSUS should include the applicable updates in their next approved deployment ring.

Workarounds

Enable Protected View for files originating from the internet and other untrusted locations.
Enforce Microsoft Office macro and ActiveX restrictions through Group Policy to limit code paths available to malicious documents.
Disable the Preview Pane in Outlook and Windows Explorer for spreadsheet file types to reduce automatic parsing exposure.
Apply Attack Surface Reduction (ASR) rules that block Office applications from creating child processes and from injecting code into other processes.

bash

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

# Verify ASR rule state
Get-MpPreference | Select-Object -ExpandProperty AttackSurfaceReductionRules_Ids