365 Apps CVE-2026-21259
HIGHCVSS VectorNVD
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Lifecycle Timeline
2DescriptionNVD
Heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to elevate privileges locally.
AnalysisAI
Privilege escalation in Microsoft Office Excel (including 365 Apps and Long Term Servicing Channel) via heap-based buffer overflow allows local attackers with user interaction to gain elevated system privileges. The vulnerability affects multiple Office product lines and currently lacks a security patch. …
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RemediationAI
Within 24 hours: Inventory all systems running affected Microsoft Office Excel versions and assess user access patterns. Within 7 days: Implement network segmentation to restrict lateral movement from compromised endpoints; disable Excel macros via Group Policy where operationally feasible; restrict local administrator privileges. …
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