High

Local Code Execution in Microsoft Office Excel

IdentifiersCVE-2026-26109CWE-125· Out-of-bounds Read

CVE-2026-26109 is an Important vulnerability in Microsoft Office Excel caused by an out-of-bounds read. According to the provided content, the flaw allows an unauthorized attacker to execute code locally. The available information identifies the weakness class as CWE-125 and provides a CVSS v3.1 vector of AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H, indicating low attack complexity and no privileges required, but local attack vector. No specific vulnerable function, file format parser, or code path is identified in the provided material.

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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 result in local code execution in the context of the vulnerable Excel environment. Based on the provided CVSS vector, the impact to confidentiality, integrity, and availability is high, meaning an attacker may be able to run arbitrary code and potentially read, modify, or disrupt data and system state accessible from the compromised context.

Mitigation

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

If immediate patching is not possible, reduce exposure by limiting local access to systems running vulnerable Microsoft Excel, restricting execution of untrusted files and content, and applying application control or endpoint protection policies to prevent unauthorized code execution from Office-related processes. Because the provided content does not specify a document-based or remote delivery vector, no more specific mitigation is currently available from the supplied material.

Remediation

Patch, then assume compromise.

Apply Microsoft's March 2026 security update for Microsoft Office Excel that addresses CVE-2026-26109. The provided content references Microsoft's MSRC Update Guide entry for this vulnerability, which should be used to identify the exact patched Office/Excel builds applicable to the affected deployment.

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 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

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

4 SOURCESView more in app

thecyberexpress com vulnerabilitiesNews

Mar 11, 2026

Microsoft Patch Tuesday March 2026: Two Zero-Days and Critical RCE Bugs Fixed - The Cyber Express

An out-of-bounds read vulnerability in Microsoft Excel that could lead to local code execution and system compromise.

cvefeed high severityNews

Mar 10, 2026

CVE-2026-26109 - Microsoft Excel Remote Code Execution Vulnerability

An out-of-bounds read vulnerability in Microsoft Office Excel that can lead to local code execution.

talos intelligence blogNews

Mar 10, 2026

Microsoft Patch Tuesday for March 2026 - Snort rules and prominent vulnerabilities

An important Microsoft Office Excel remote code execution vulnerability caused by an out-of-bounds read that could allow local code execution.

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 activity1

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

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2026-26109

NVD

nvd.nist.gov/vuln/detail/CVE-2026-26109

MITRE CWE · CWE-125

Out-of-bounds Read

Vendor Advisory

msrc.microsoft.com/update-guide/vulnerability/CVE-2026-26109