Microsoft Office Excel: Remote code execution via heap-based buffer overflow
Summary
A heap-based buffer overflow in Microsoft Office Excel allows an unauthenticated attacker to execute code over the network. The CVSS base score is 8.8 (HIGH). Exploitation requires that a user opens or otherwise processes a crafted Excel file; a secondary source indicates that the Preview Pane may be sufficient, which Microsoft's text has not confirmed. A successful attack would run with the rights of the user.
Affected
- Microsoft 365 Apps for Enterprise (16.0.1 onward, per CNA data)
- Microsoft Office LTSC 2021 and LTSC 2024
- Microsoft Office 365 for Mac and Office LTSC for Mac 2021 and 2024
- Fixed build numbers: unverified, see recommendation
Fixed in
- Apply the Microsoft Office security updates released on 13 October 2026.
- Exact fixed build numbers per channel: Unknown. The CNA data and a third-party aggregator conflict; check the MSRC build table.
Workaround
- Unknown. No workaround is documented by Microsoft in the sources reviewed.
- Unverified option: disable the Preview Pane for Excel files until patched, but only if this is supported in your environment.
Exploitation
- Not listed in CISA's Known Exploited Vulnerabilities catalog.
- CISA SSVC data: exploitation none, automatable no, technical impact total.
- EPSS 0.00722 (low).
- No public proof of concept or exploitation reports found in a limited search.
Our recommendation
- Treat as high priority.
- Deploy the October 2026 Office updates to all Microsoft 365 and Office LTSC clients, including Mac.
- Verify the exact fixed build numbers on the MSRC page before rollout.
- Prioritise staff who handle external or emailed Excel files.
- Check patch levels afterwards, for example with vulnerability scanners that support Office update checks.
- Monitor for exploitation reports and re-check this entry.
Information from Microsoft (Patch Tuesday October 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-88145 msrc.microsoft.com
- Microsoft 365 Apps security updates learn.microsoft.com
- Zero Day Initiative: October 2026 security update review www.zerodayinitiative.com
- OpenCVE: CVE-2026-88145 app.opencve.io
- Vulners: CVE-2026-88145 vulners.com
- Strix: CVE-2026-88145 www.strix.ai
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, 18:07.
Original description (NVD)
Heap-based buffer overflow in Microsoft Office Excel 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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