Microsoft Security Update Guide · Office / Microsoft 365 Apps
Microsoft Office Outlook Remote Code Execution Vulnerability
Published · updated 30 sep 2026
What does this mean?
- Remote Code Execution. An attacker can run their own code on the system remotely. This is the most serious type: it can lead to taking over the system.
- It can be exploited over the network (including from the internet if the service is reachable there), without an account and if a user takes part, for example by opening a link or file.
- CVSS 8.8 out of 10: high. Microsoft rates it Important.
- No attacks reported; Microsoft expects exploitation to be less likely.
- What should you do? Install the security update for the version you run (or a later cumulative update):
- Microsoft Office LTSC 2024 for 64-bit editions: KBClick to Run
https://aka.ms/OfficeSecurityReleases - Microsoft Office LTSC 2024 for 32-bit editions: KBClick to Run
https://aka.ms/OfficeSecurityReleases - Microsoft 365 Apps for Enterprise for 32-bit Systems: KBClick to Run
https://aka.ms/OfficeSecurityReleases - Microsoft Office LTSC 2021 for 64-bit editions: KBClick to Run
https://aka.ms/OfficeSecurityReleases - Microsoft Office LTSC 2021 for 32-bit editions: KBClick to Run
https://aka.ms/OfficeSecurityReleases - Microsoft 365 Apps for Enterprise for 64-bit Systems: KBClick to Run
https://aka.ms/OfficeSecurityReleases
- Microsoft Office LTSC 2024 for 64-bit editions: KBClick to Run
Outlook Office / Microsoft 365 Apps
What kind of flaw is this?
- CWE-122: Heap-based Buffer Overflow
A heap buffer overflows, which can lead to running code.
Key facts
Released
23 sep 2026
Last revised
30 sep 2026 (v1.2)
Impact
Remote Code Execution
Max severity
Important
Weakness
CVSS 3.1
8.8 / 7.7 (base / temporal)
Vector string
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:CPublicly disclosed
No
Exploited
No
Exploitability assessment
Exploitation Less Likely
Customer action required
Yes
Links
CVSS metrics
| Base score metrics | |
|---|---|
| Attack Vector | Network |
| Attack Complexity | Low |
| Privileges Required | None |
| User Interaction | Required |
| Scope | Unchanged |
| Confidentiality | High |
| Integrity | High |
| Availability | High |
| Temporal score metrics | |
| Exploit Code Maturity | Unproven |
| Remediation Level | Official Fix |
| Report Confidence | Confirmed |
Affected products and updates
| Product | Update | Build |
|---|---|---|
| Microsoft Office LTSC 2024 for 64-bit editions | KBClick to Run | https://aka.ms/OfficeSecurityReleases |
| Microsoft Office LTSC 2024 for 32-bit editions | KBClick to Run | https://aka.ms/OfficeSecurityReleases |
| Microsoft 365 Apps for Enterprise for 32-bit Systems | KBClick to Run | https://aka.ms/OfficeSecurityReleases |
| Microsoft Office LTSC 2021 for 64-bit editions | KBClick to Run | https://aka.ms/OfficeSecurityReleases |
| Microsoft Office LTSC 2021 for 32-bit editions | KBClick to Run | https://aka.ms/OfficeSecurityReleases |
| Microsoft 365 Apps for Enterprise for 64-bit Systems | KBClick to Run | https://aka.ms/OfficeSecurityReleases |
FAQ
- According to the CVSS metric, user interaction is required (UI:R). What interaction would the user have to do?
- An attacker must send a user a malicious Office file and convince them to open it.
Revisions
| Version | Date | Note |
|---|---|---|
| 1.2 | 30 sep 2026 | CWE added. Informational change only. |
| 1 | 23 sep 2026 | Information published. |
| 1.1 | 23 sep 2026 | Information published. This CVE was addressed by updates that were released in September 2026, but the CVE was inadvertently omitted from the September 2026 Security Updates. This is an informational change only. Customers who have already installed the September 2026 updates do not need to take any further action. |
This is in the weekly digest for week 40 · What changed this week? →
View at Microsoft → ← All security advisories
Source: Microsoft Security Update Guide. 365Fanatic is not affiliated with Microsoft.
