Heap-based buffer overflow in Microsoft products - CVE-2026-21259
Published: February 10, 2026
Vulnerability identifier: #VU122583
CSH Severity: High
CVSS v4.0: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber
CVE-ID: CVE-2026-21259
CWE-ID: CWE-122
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Microsoft
Affected software:
Office Online Server
Microsoft Office
Microsoft Excel
Microsoft 365 Apps for Enterprise
Microsoft Office LTSC
Office Online Server
Microsoft Office
Microsoft Excel
Microsoft 365 Apps for Enterprise
Microsoft Office LTSC
Detailed vulnerability description
The vulnerability allows a remote attacker to escalate privileges on the target system.
The vulnerability exists due to a boundary error in Microsoft Excel. A remote attacker can pass specially crafted data to the application, trigger a heap-based buffer overflow and gain elevated privileges on the system.
How to mitigate CVE-2026-21259
Install updates from vendor's website.