Vulnerability · Published Sep 8, 2026 · Assigned by microsoft
CVE-2026-78509Microsoft Office Outlook Remote Code Execution Vulnerability
Critical 9.8
In plain English
A critical-severity heap buffer overflow in Microsoft 365 Apps for Enterprise from Microsoft. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 1.0% (higher than 62% of all known vulnerabilities).
Severity (CVSS 3.1)9.8Critical
Exploit odds (30 days)1.0%top 37.8% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
Heap-based buffer overflow in Microsoft Office Outlook allows an unauthorized attacker to execute code over a network.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Microsoft | Microsoft 365 Apps for Enterprise | 16.0.1 – before 16.0.20326.20138 |
| Microsoft | Microsoft Office 2019 | 19.0.0 – before 16.0.10417.20207 |
| Microsoft | Microsoft Office 365 for Mac | 1.0.0 – before 16.113.26091433 |
| Microsoft | Microsoft Office LTSC 2021 | 16.0.1 – before 16.0.14334.20906 |
| Microsoft | Microsoft Office LTSC 2024 | 16.0.0 – before 16.0.17932.20976 |
| Microsoft | Microsoft Office LTSC for Mac 2021 | 16.0.1 – before 16.113.26091433 |
| Microsoft | Microsoft Office LTSC for Mac 2024 | 16.0.0 – before 16.113.26091433 |
| Microsoft | Microsoft Word 2016 | 16.0.1 – before 16.0.5569.1000 |
Weakness: CWE-122 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
References
- Microsoft Office Outlook Remote Code Execution Vulnerability vendor-advisory, patch