Microsoft Office Word: Heap-based buffer overflow enables remote code execution
Summary
A heap-based buffer overflow in Microsoft Word, part of Microsoft 365 Apps and Office LTSC 2021/2024 on Windows and Mac, allows remote code execution. An attacker can run code on the victim's system by tricking the user into opening a crafted Word document, for example from an email or a download. No privileges are required, but user interaction is needed. Microsoft rates the issue Important (CVSS 3.1: 8.8).
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 up to the fixed build (see MSRC link)
- Microsoft Office 365 for Mac: 1.0.0 to < 16.114.26101123
- Microsoft Office LTSC 2021: 16.0.1 to < 16.0.14334.20974
- Microsoft Office LTSC 2024: 16.0.0 to < 16.0.17932.21056
- Microsoft Office LTSC for Mac 2021: 16.0.1 to < 16.114.26101123
- Microsoft Office LTSC for Mac 2024: 16.0.0 to < 16.114.26101123
Fixed in
- Windows: security updates released October 13, 2026 for Office LTSC 2024 and LTSC 2021 (32-bit) per MSRC. Microsoft 365 Apps: see the MSRC table for the build per channel.
- Mac (Office 365 and LTSC for Mac 2021/2024): no fix available yet. Microsoft says updates will follow as soon as possible.
Workaround
Unknown.
Exploitation
- Not listed in CISA KEV.
- CISA SSVC: exploitation none, not automatable, total technical impact.
- MSRC exploit code maturity: unproven.
- EPSS about 0.9% in one aggregator (date unknown).
- No public proof of concept or in-the-wild exploitation found in the research.
Our recommendation
- Patch Windows installations of Microsoft 365 Apps, Office LTSC 2021 and LTSC 2024 to the build listed for your channel in the MSRC table.
- Treat Mac installations as unpatched until Microsoft releases a fixed build, and restrict opening untrusted documents on Mac.
- Enforce attachment filtering and open documents from external senders in Protected View or a sandbox.
- Monitor the MSRC page and CISA KEV for changes in exploitation status.
Information from Microsoft (Patch Tuesday October 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- MSRC Security Update Guide: CVE-2026-70301 msrc.microsoft.com
- Microsoft 365 Apps security updates learn.microsoft.com
- OpenCVE: CVE-2026-70301 app.opencve.io
- Vulners NVD record: CVE-2026-70301 vulners.com
- Strix: CVE-2026-70301 www.strix.ai
- GitHub vulnerability alert: CVE-2026-70301 github.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 31 Oct 2026, 18:42.
Original description (NVD)
Heap-based buffer overflow in Microsoft Office Word allows an unauthorized attacker to execute code over a network.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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