Sources: National Vulnerability Database, CVE.org, CISA KEV, FIRST EPSS
CVE-2026-118705 Overview
Heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code over a network.
Critical Impact
Affected Products
- Microsoft Office Excel: see the vendor advisory for the exact affected versions
Discovery Timeline
- 2026-11-10: CVE-2026-118705 published to the National Vulnerability Database by secure@microsoft.com
- 2026-11-10: last updated in the NVD database
Technical Details for CVE-2026-118705
Vulnerability Analysis
CVE-2026-118705 is a Heap Buffer Overflow weakness (CWE-122: Heap Buffer Overflow) in Microsoft Office Excel. Based on its CVSS vector, the flaw can be reached over the network, needs no login, and relies on a user taking an action. A write past the end of a heap buffer corrupts nearby memory.
With a CVSS base score of 8.8, apply the vendor fix and confirm exposure on internet facing and business critical assets first.
Root Cause
The weakness is classified as CWE-122: Heap Buffer Overflow. A write past the end of a heap buffer corrupts nearby memory.
Attack Vector
Based on the CVSS vector, the flaw can be reached over the network, needs no login, and relies on a user taking an action. Attack complexity is low complexity.
No exploitation in the wild is confirmed by CISA at the time of the last update. Check the references below for any vendor or researcher proof of concept.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Detection Methods for CVE-2026-118705
Detection Strategies
- Inventory every instance of Microsoft Office Excel and compare the running version with the affected range above.
- Check external attack surface scans for internet facing instances of the component.
- Run an authenticated vulnerability scan once your scanner ships a check for this CVE.
Monitoring Recommendations
- Forward Microsoft Office Excel application, access and audit logs to your SIEM for retrospective hunting.
- Alert on new processes, configuration changes or outbound connections from the affected service.
- Track the vendor advisory and the CISA KEV catalog for changes in exploitation status.
How to Mitigate CVE-2026-118705
Immediate Actions Required
- Apply the fixed version of Microsoft Office Excel named in the vendor advisory.
- Prioritize internet facing and business critical instances first.
- Rescan after the change to confirm the exposure is closed.
Patch Information
Use the fixed version listed in the vendor advisory for Microsoft Office Excel.
Workarounds
- If patching must wait, restrict network access to the affected service and place it behind authentication or a web application firewall rule.
CWE References
- CWE-122: Heap Buffer Overflow More CVEs with this weakness
Technical References
This entry is built directly from NVD, CISA KEV and EPSS data. Verify fixed versions in the vendor advisory before you deploy.
Frequently asked questions
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