EUVD-2026-56432
GHSA-72mj-qw76-gff7
Severity by source
AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
AV:L because the malicious file must be locally opened; PR:N since no prior authentication is needed; UI:R because the user must open the crafted document to trigger the overflow.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
3DescriptionCVE.org
Heap-based buffer overflow in Microsoft Office allows an unauthorized attacker to execute code locally.
AnalysisAI
Heap-based buffer overflow in Microsoft Office enables arbitrary local code execution when a user opens a specially crafted document. Affected products span seven product lines across Windows and macOS, including Office 2019, Office LTSC 2021/2024, Microsoft 365 Apps for Enterprise, and their Mac counterparts, all prior to the vendor-released patch. No public exploit or CISA KEV listing has been identified at time of analysis, but the breadth of the affected install base and the low-complexity exploitation path make this a high-priority patching item.
Technical ContextAI
CWE-122 (Heap-based Buffer Overflow) describes the root cause: data written to a heap-allocated buffer exceeds its bounds, corrupting adjacent heap metadata and enabling an attacker to redirect code execution. In Microsoft Office, this class of flaw typically manifests during document parsing - processing binary or XML structures in formats such as .docx, .xlsx, or .pptx - where complex nested objects can overflow fixed-size allocations. The CVSS vector specifies a local attack vector (AV:L), consistent with exploitation being triggered at file-open time within the Office process context. Affected product lines confirmed via EUVD-2026-56432 include Microsoft Office 2019 (19.0.0 and above), Office LTSC 2021 and 2024 (from 16.0.1 and 16.0.0 respectively), Microsoft 365 Apps for Enterprise (from 16.0.1), and macOS equivalents: Office 365 for Mac (from 1.0.0), Office LTSC for Mac 2021 (from 16.0.1), and Office LTSC for Mac 2024 (from 16.0.0).
RemediationAI
The primary fix is to apply the vendor-released patch immediately. macOS users should upgrade to Office build 16.112.26081010 or later, which addresses all three affected Mac product lines (Office 365 for Mac, LTSC for Mac 2021, LTSC for Mac 2024). Windows users running Office 2019, LTSC 2021, LTSC 2024, or Microsoft 365 Apps for Enterprise should apply updates referenced at https://aka.ms/OfficeSecurityReleases; the precise Windows build number is not enumerated in the available data and should be confirmed via the MSRC advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-65664. Pending patching, administrators should enforce Office Protected View for documents received from external sources (File > Options > Trust Center > Protected View), which renders documents in a sandboxed read-only mode and prevents automatic exploit triggering - note that Protected View bypass techniques exist, so this is a mitigation, not a fix. Enabling Microsoft Defender for Endpoint Attack Surface Reduction (ASR) rule 'Block Office applications from creating child processes' (d4f940ab-401b-4efc-aadc-ad5f3c50688a) provides additional containment if exploitation succeeds. Blocking or sandboxing Office document attachments at the email gateway until patching is complete is a high-effectiveness compensating control with the trade-off of disrupting document-heavy workflows.
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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
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