Heap-based buffer overflow in Microsoft products - CVE-2026-21259
Published: February 10, 2026
Vulnerability identifier: #VU122583
CSH Severity: High
CVSS v4: 8.4 [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]
CVE-ID: CVE-2026-21259
CWE-ID: CWE-122
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
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.
Affected software
Office Online Server
Microsoft 365 Apps for Enterprise
Microsoft Excel
Microsoft Office
Microsoft Office LTSC
Microsoft 365 Apps for Enterprise
Microsoft Excel
Microsoft Office
Microsoft Office LTSC
How to mitigate CVE-2026-21259
Install updates from vendor's website.