CVE-2026-78509

CRITICAL

Heap-based buffer overflow in Microsoft Office Outlook allows an unauthorized attacker to execute code over a network.

CVSS v3.1 Score

9.8
CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
HIGH
Published: 9/8/2026Modified: 9/9/2026

Related Intelligence (1)

CRITICALRansomware

Patch Tuesday - September 2026

Microsoft is publishing 974 own-product vulnerabilities on September 2026 Patch Tuesday , including 723 vulnerabilities in Windows. Along with Microsoft fixes for 25 non-Microsoft CVEs, that brings the total number of vulnerabilities on the table today to 999. Whether this is the biggest Patch Tuesday ever depends on how we count, but this is by far the most CVEs that Microsoft has ever published

CVE-2026-85880CVE-2026-81963
Rapid7

References (1)

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-78509PatchVendor Advisory