EUVD-2026-44219
GHSA-j39m-7jfm-44r6
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessCraft malicious OneNote file
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DeliveryDeliver via phishing or shared link
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ExploitVictim opens document in OneNote
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ExecutionTrigger heap buffer overflow in parser
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PersistCorrupt heap and hijack control flow
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ImpactExecute arbitrary code as current user
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 a victim to open an attacker-supplied malicious OneNote file on an affected build (Microsoft 365 Apps for Enterprise or Office for Mac 2021/2024/365) - the CVSS UI:R metric confirms mandatory user interaction, which is the key limiting factor. No prior authentication or elevated privileges are needed (PR:N), and no special product configuration is called out in the description, but the AV:L vector means the attacker cannot trigger this purely over the network: the malicious file must reach and be opened locally by the user. Code executes in the context of the opening user, so a low-privilege victim limits blast radius absent further privilege escalation. |
| Impact | Signals are moderately consistent and point to real-but-not-emergency priority. The CVSS 3.1 vector (AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H, base 7.8) reflects a client-side file-open flaw: no privileges needed but user interaction is required, so mass automated exploitation is unlikely. This aligns with CISA SSVC, which rates Exploitation: none and Automatable: no while Technical Impact: total - meaning full compromise is possible if triggered, but not at scale. No EPSS score was provided in the input, and there is no KEV listing and no public exploit identified at time of analysis, so this is not confirmed under active exploitation. The primary caveat: PR:N combined with UI:R means 'unauthenticated' in the CVSS sense but exploitation still hinges on social engineering the victim into opening a malicious file - treat it as a phishing-delivered client RCE rather than a wormable network bug. |
| Exploit ScenarioDerived | An attacker emails or shares a crafted OneNote document that triggers the heap overflow when parsed; a targeted user opens the file, and the malformed structure corrupts the heap to execute the attacker's code in the user's security context. Because the vector is local with required user interaction (AV:L/UI:R), the attack is realistically delivered via phishing or a watering-hole download rather than remotely without victim action. No public exploit is identified at time of analysis. |
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Alert meAnalysisAIv1 – Jul 14, 2026
Local code execution in Microsoft Office OneNote (Microsoft 365 Apps for Enterprise and Office for Mac editions) arises from a heap-based buffer overflow (CWE-122) that lets an attacker run arbitrary code in the context of the current user when a victim opens a maliciously crafted OneNote file. The CVSS 3.1 score is 7.8 with a local attack vector requiring user interaction (AV:L/UI:R), and impact is total across confidentiality, integrity, and availability. There is no public exploit identified at time of analysis, and CISA SSVC lists exploitation status as none.
RemediationAI
Patch available per vendor advisory: apply the Microsoft Office/OneNote security update referenced at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55133 for your channel - Microsoft 365 Apps for Enterprise, Office 365 for Mac, and Office LTSC for Mac 2021/2024. The exact fixed build was not provided in the input, so pull the specific version from the MSRC update guide and roll it via your normal Office update channel (Click-to-Run/AutoUpdate for Mac). Until patched, the practical compensating control is to block delivery and opening of untrusted OneNote files: filter .one/.onepkg attachments at the mail gateway, restrict OneNote file associations, and instruct users not to open OneNote documents from untrusted sources - the trade-off is reduced convenience for legitimate OneNote sharing. Endpoint protection and macro/attachment policies reduce phishing delivery but do not remove the underlying heap overflow, so patching remains the only complete fix.
Affected VersionsENISA
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 3 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 vulnerability is a heap-based buffer overflow (CWE-122), a memory-safety flaw where OneNote's parser allocates a heap buffer and then writes past its bounds while processing attacker-controlled data - likely embedded objects or malformed structures inside a crafted OneNote (.one/.onepkg) document. Corrupting adjacent heap metadata or object pointers can be leveraged to hijack control flow and achieve arbitrary code execution in the process context. Per the CPE data the affected code ships in cpe:2.3:a:microsoft:microsoft_365_apps_for_enterprise, microsoft_office_365_for_mac, microsoft_office_ltsc_for_mac_2021, and microsoft_office_ltsc_for_mac_2024, indicating the defect is in the shared OneNote component across both the Windows-oriented Microsoft 365 Apps channel and the macOS Office builds.
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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 client RCE: local vector and required user interaction (AV:L/UI:R), no privileges needed (PR:N), full code execution yields total C/I/A impact.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
DescriptionCVE.org
Heap-based buffer overflow in Microsoft Office OneNote allows an unauthorized attacker to execute code locally.
Executive ViewAI
Microsoft Office OneNote (Microsoft 365 Apps for Enterprise and Office for Mac) contains a heap-based buffer overflow vulnerability (CVE-2026-55133) that enables arbitrary code execution when users open maliciously crafted files. Any employee receiving a crafted OneNote file could have their workstation compromised, exposing sensitive data and creating a malware installation vector across the organization. Patch deployment is critical to mitigate this user-facing endpoint risk.
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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Exploit-DB