Microsoft Office Excel: Remote code execution via integer overflow
Summary
An integer overflow (CWE-190) in Microsoft Office Excel allows an unauthenticated attacker to execute code over the network. The attack requires that a user opens a crafted Excel file, most likely delivered by email or download. A successful attack runs code in the context of the user, and the CVSS 3.1 base score is 8.8 (High). Office Online Server is server-side, so on-premises instances need separate attention.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 up to the fixed release (exact fixed build unknown from the sources; see the MSRC advisory)
- Office 365 for Mac: 1.0.0 to before 16.114.26101123
- Office LTSC 2021: 16.0.1 to before 16.0.14334.20974
- Office LTSC 2024: 16.0.0 to before 16.0.17932.21056
- Office LTSC for Mac 2021: 16.0.1 to before 16.114.26101123
- Office LTSC for Mac 2024: 16.0.0 to before 16.114.26101123
- Office Online Server: 16.0.0.0 to before 16.0.10417.20228
Fixed in
- Office LTSC 2021: 16.0.14334.20974 (per CVE record; verify with MSRC)
- Office LTSC 2024: 16.0.17932.21056 (unverified, only from a third-party aggregator)
- Office 365 for Mac: 16.114.26101123 (per CVE record; confirm in Microsoft release notes)
- Office Online Server: 16.0.10417.20228 (per CVE record)
- Microsoft 365 Apps for Enterprise: build unknown
- Office LTSC for Mac 2021/2024: build unknown
Workaround
Unknown. Microsoft has not published an official workaround; patching is the fix.
Exploitation
- Microsoft rates exploitation as less likely.
- Microsoft's exploit code maturity is Unproven.
- CISA SSVC (ADP record): exploitation none, automatable no.
- No public proof-of-concept found in the research; this does not prove that none exists.
- No CISA KEV listing found in the searches; check the KEV catalog directly.
Our recommendation
- Install the October 2026 security updates for all Microsoft Office and Excel installations, prioritising Office Online Server and on-premises systems.
- Verify the fixed build for each product in the MSRC advisory before rollout.
- Until patched, block or quarantine Excel files from untrusted email and downloads.
- Check whether Office Online Server is in use on-premises.
- Monitor for exploitation reports and the CISA KEV catalog.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Critical
- Impact
- Remote code execution – Microsoft Office Excel
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Microsoft Office
- Updates (KB)
- KB5002928
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-97778 msrc.microsoft.com
- Microsoft Security Update Guide: CVE-2026-97778 advisory msrc.microsoft.com
- Action1: Patch Tuesday October 2026 www.action1.com
- Qualys: Microsoft Patch Tuesday October 2026 review threatprotect.qualys.com
- Microsoft Office for Mac release notes learn.microsoft.com
- Vulners: CVE-2026-97778 vulners.com
- OpenCVE: CVE-2026-97778 app.opencve.io
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, 17:23.
Original description (NVD)
Integer overflow or wraparound 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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