EUVD-2026-44219
GHSA-j39m-7jfm-44r6
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
Lifecycle Timeline
2DescriptionCVE.org
Heap-based buffer overflow in Microsoft Office OneNote allows an unauthorized attacker to execute code locally.
AnalysisAI
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.
Technical ContextAI
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.
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.
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Same weakness CWE-122 – Heap-based Buffer Overflow
View allSame technique Buffer Overflow
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External POC / Exploit Code
Leaving vuln.today