High

Remote Code Execution in Microsoft Office Excel

IdentifiersCVE-2026-40362CWE-122· Heap-based Buffer Overflow

CVE-2026-40362 is a Microsoft Office Excel memory corruption vulnerability that can lead to code execution. Available reporting identifies the issue as a heap-based buffer overflow in Excel, while another description characterizes it as a use-after-free condition; based on the vendor-associated weakness mapping, the vulnerability is best classified as CWE-122. The flaw is triggered when Excel processes a specially crafted Office file, causing unsafe memory handling in the application and enabling attacker-controlled code execution in the context of the user who opened the file. Although described as a remote code execution vulnerability, exploitation occurs through local processing of malicious content after delivery to the target system, typically via social engineering.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation can allow arbitrary code execution in the security context of the current user. Given the stated high impacts to confidentiality, integrity, and availability, an attacker could potentially read or modify accessible data, install or run additional payloads, and disrupt system or application availability. No privileges are required prior to exploitation, but user interaction is required to open the malicious file.

Mitigation

If you can’t patch tonight, do this now.

Reduce exposure by preventing users from opening untrusted or unsolicited Office documents, especially those received through email or downloaded from the internet. Use protected document handling controls, attachment filtering, application control, and user awareness measures to limit execution of malicious Office content. The Preview Pane is not an attack vector for this vulnerability, so mitigation should focus on blocking or isolating document opening rather than preview behavior. Prioritize patch deployment because no separate vendor workaround is identified in the available information.

Remediation

Patch, then assume compromise.

Apply the Microsoft security update that addresses CVE-2026-40362 for affected Microsoft Office and Excel installations. Vendor-issued fixes were available at the time of disclosure. Ensure Office deployments are updated through the relevant Microsoft security bulletin for the release cycle in which this vulnerability was corrected.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

Microsoft Corporation365 Appsapplication

Microsoft CorporationExcelapplication

Microsoft CorporationExcel 2016application

Microsoft CorporationOfficeapplication

Microsoft CorporationOffice 2019application

Microsoft CorporationOffice 2021application

Microsoft CorporationOffice 2024application

Microsoft CorporationOffice Excelapplication

Microsoft CorporationOffice Long Term Servicing Channelapplication

Microsoft CorporationOffice Macos 2021application

Microsoft CorporationOffice Macos 2024application

Microsoft CorporationOffice Online Serverapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

3 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

3 SOURCESView more in app

msrc microsoftNews

May 12, 2026

CVE-2026-40362 - Security Update Guide - Microsoft - Microsoft Excel Remote Code Execution Vulnerability

A heap-based buffer overflow remote code execution vulnerability in Microsoft Office Excel that requires user interaction, typically by convincing a victim to open a malicious Office file.

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.

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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2026-40362

NVD

nvd.nist.gov/vuln/detail/CVE-2026-40362

MITRE CWE · CWE-122

Heap-based Buffer Overflow

Vendor Advisory

msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40362

Remote Code Execution in Microsoft Office Excel

IdentifiersCVE-2026-40362CWE-122· Heap-based Buffer Overflow