EUVD-2026-29644
GHSA-qxwr-vc23-g88h
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessCraft malicious Excel spreadsheet
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DeliveryDeliver via phishing email or link
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ExploitVictim opens file and enables editing
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ExecutionTrigger heap buffer overflow in parser
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PersistHijack control flow, execute code as user
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ImpactEstablish foothold for lateral movement
Vulnerability Assessment
| Weakness |
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Heap buffer bounds checking
MITRE ATT&CK
1 technique across 1 tactic: Execution The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Exploitation Conditions | Exploitation requires the victim to open an attacker-crafted Excel/Office document in a vulnerable build - this user-interaction requirement (UI:R) is the primary limiting factor. The attacker needs no prior privileges or authentication on the target (PR:N) and the attack is local (AV:L), meaning it executes through file handling rather than a network service. Limiting factors that reduce real-world risk: Office Protected View / Mark-of-the-Web sandboxing must be bypassed or disabled by the user, the target must run an unpatched version listed above, and SSVC marks the flaw as not automatable (no mass/wormable exploitation). Office Online Server is an exception where server-side document processing can reduce the user-interaction dependency. |
| Impact | The signals are largely consistent and point to a serious-but-not-emergency issue. CVSS 7.8 (High) reflects local vector with low complexity, no privileges, but required user interaction (AV:L/AC:L/PR:N/UI:R) and total CIA impact. SSVC agrees on total technical impact but rates exploitation as 'none' and automatable as 'no' - consistent with the low EPSS (0.06%, 18th percentile) and the absence of a public POC or CISA KEV listing. In short, real impact is high (code execution) but current real-world exploitation likelihood is low because it needs a user to open a crafted file and cannot be mass-automated. One nuance to verify: PR:N in the CVSS vector formally means no authentication, yet exploitation genuinely depends on user interaction (opening the document), so this is unauthenticated in the CVSS sense but not zero-touch. Prioritize patching for high-value/targeted users, but this is not a drop-everything internet-facing worm. |
| Exploit ScenarioDerived | An attacker emails a finance employee a spreadsheet that appears to be an invoice or report; when the victim opens it (and leaves Protected View or clicks 'Enable Editing'), a crafted record overflows a heap buffer in Excel and runs shellcode as that user, giving the attacker a foothold for credential theft or lateral movement. No public POC exists at time of analysis, and the low complexity (AC:L) means a reliable exploit, once developed, would work consistently against unpatched targets. |
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Alert meAnalysisAIv1 – Jul 23, 2026
Arbitrary code execution in Microsoft Excel (and the broader Office family through Microsoft 365 Apps, Office 2019, LTSC 2021/2024, Office for Mac, and Office Online Server) is possible when a user opens a maliciously crafted spreadsheet that triggers a heap-based buffer overflow (CWE-122), running attacker code in the context of the current user. There is no public exploit identified at time of analysis and the EPSS probability is very low (0.06%, 18th percentile), but the technical impact is total (full confidentiality, integrity, and availability loss). Microsoft has released patches; exploitation requires the victim to open a file, so it is a phishing/social-engineering-driven local vulnerability rather than a remotely wormable one.
RemediationAI
Apply Microsoft's security update per the MSRC advisory (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40362): update Excel 2016 to 16.0.5552.1000, Office for Mac 2021/2024 to 16.109.26051019, and Office Online Server to 16.0.10417.20128; for Microsoft 365 Apps, Office 2019, and Office LTSC 2021/2024 install the latest channel update via https://aka.ms/OfficeSecurityReleases. Because exploitation requires opening a crafted file, effective compensating controls until patching completes include enforcing Protected View and blocking files originating from the internet/email (Mark-of-the-Web), enabling Office macro and Trust Center restrictions, and using attack-surface-reduction rules to limit Office child-process creation - trade-off is some friction for users who legitimately edit externally sourced spreadsheets. For Office Online Server, restrict and patch the rendering host promptly since server-side parsing of untrusted documents removes the per-user interaction barrier. Do not rely on email filtering alone.
Affected VersionsENISA
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 4 packages in euvd
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
The flaw is a CWE-122 heap-based buffer overflow in the file-parsing code of Microsoft's Office/Excel document engine. Excel processes complex binary and OOXML spreadsheet structures, and a malformed record can cause the parser to write past the bounds of a heap-allocated buffer, corrupting adjacent heap metadata or object pointers and enabling control-flow hijack. The CPE set confirms the shared code affects multiple delivery channels of the same Office engine: microsoft_365_apps_for_enterprise, microsoft_excel_2016, microsoft_office_2019, microsoft_office_ltsc_2021, microsoft_office_ltsc_2024, microsoft_office_ltsc_for_mac_2021, microsoft_office_ltsc_for_mac_2024, and office_online_server - meaning both Windows and macOS builds, and the server-side Office Online Server rendering component, are in scope.
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Severity by source
AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
File-open exploitation gives AV:L and UI:R with no prior privileges (PR:N); reliable heap overflow yields low complexity and total CIA impact within the user's context (S:U).
Primary rating from NVD.
CVSS VectorNVD
DescriptionCVE.org
Heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
Executive ViewAI
A heap-based buffer overflow in Microsoft Excel and Office products enables attackers to execute arbitrary code when users open malicious spreadsheets, potentially leading to data theft or system compromise. No public exploit has been identified at time of analysis; however, the vulnerability affects the majority of organizations through their Office deployments and is primarily delivered via phishing or social engineering. The broad user base and complete technical impact warrant urgent patching across all affected Office versions.
Apply vendor patch.
Threat Intelligence Overview
NVD
CVE.org
EPSS
Vulnrichment
VulDB
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.
A heap overflow occurs when a program writes data beyond the bounds of a buffer allocated in the heap memory region.
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