CVE-2026-40358: Microsoft Office Remote Code Execution Vulnerability
CVE-2026-40358 is a remote code execution vulnerability in Microsoft Office, rated Critical by Microsoft, with a CVSS 3.1 base score of 8.4 (High). An attacker can exploit it by an attacker with local access, without any privileges and without user interaction. Microsoft has not reported exploitation in the wild and rates exploitation as less likely. The EPSS model estimates a 0.37% probability of exploitation activity in the next 30 days, higher than 31% of all scored vulnerabilities. Microsoft released the fix on 12 May 2026 in the May 2026 Patch Tuesday, delivered through 1 security update (KB5002866). It affects 12 products in 1 product family (Microsoft Office).
Key facts
- CVE ID
- CVE-2026-40358
- Severity
- High CVSS 8.4
- Microsoft severity
- Critical
- Impact
- Remote Code Execution
- Exploited in the wild
- No
- Publicly disclosed
- No
- Exploitation likelihood
- Less Likely
- Weakness
- CWE-416
- EPSS
- 0.37% (percentile 31%)
- CISA KEV
- Not listed
- Released
- Last updated
- Patch Tuesday
- May 2026 Patch Tuesday
- Product families
- Microsoft Office
CVSS score and vector
Microsoft scores CVE-2026-40358 at 8.4 (temporal 7.3) using CVSS 3.1. Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
| Metric | Value |
|---|---|
| Attack vector | Local |
| Attack complexity | Low |
| Privileges required | None |
| User interaction | None |
| Scope | Unchanged |
| Confidentiality impact | High |
| Integrity impact | High |
| Availability impact | High |
| Exploit code maturity | Unproven |
| Remediation level | Official fix |
| Report confidence | Confirmed |
Description
Heap-based buffer overflow in Microsoft Office allows an unauthorized attacker to execute code locally.
Frequently asked questions (Microsoft)
Is the Preview Pane an attack vector for this vulnerability?
Yes, the Preview Pane is an attack vector.
According to the CVSS metric, the attack vector is local (AV:L). Why does the CVE title indicate that this is a remote code execution?
The word Remote in the title refers to the location of the attacker. This type of exploit is sometimes referred to as Arbitrary Code Execution (ACE). The attack itself is carried out locally.
For example, when the score indicates that the Attack Vector is Local and User Interaction is Required, this could describe an exploit in which an attacker, through social engineering, convinces a victim to download and open a specially crafted file from a website which leads to a local attack on their computer.
Affected products (12)
Microsoft Office
| Product | Security update | Type | Fixed build | Restart |
|---|---|---|---|---|
| Microsoft Office 2019 for 32-bit editions | Click to Run | Security Update | https://aka.ms/OfficeSecurityReleases | No |
| Microsoft Office 2019 for 64-bit editions | Click to Run | Security Update | https://aka.ms/OfficeSecurityReleases | No |
| Microsoft 365 Apps for Enterprise for 32-bit Systems | Click to Run | Security Update | https://aka.ms/OfficeSecurityReleases | No |
| Microsoft 365 Apps for Enterprise for 64-bit Systems | Click to Run | Security Update | https://aka.ms/OfficeSecurityReleases | No |
| Microsoft Office LTSC for Mac 2021 | Release Notes | Security Update | 16.109.26051019 | Maybe |
| Microsoft Office LTSC 2021 for 64-bit editions | Click to Run | Security Update | https://aka.ms/OfficeSecurityReleases | No |
| Microsoft Office LTSC 2021 for 32-bit editions | Click to Run | Security Update | https://aka.ms/OfficeSecurityReleases | No |
| Microsoft Office LTSC 2024 for 32-bit editions | Click to Run | Security Update | https://aka.ms/OfficeSecurityReleases | No |
| Microsoft Office LTSC 2024 for 64-bit editions | Click to Run | Security Update | https://aka.ms/OfficeSecurityReleases | No |
| Microsoft Office LTSC for Mac 2024 | Release Notes | Security Update | 16.109.26051019 | Maybe |
| Microsoft Office 2016 (32-bit edition) | KB5002866 | Security Update | 16.0.5552.1000 | Maybe |
| Microsoft Office 2016 (64-bit edition) | KB5002866 | Security Update | 16.0.5552.1000 | Maybe |
Security updates (1)
- KB5002866 (Security Update)
NIST NVD data
- NVD status
- Modified
- NVD CVSS
- 8.4 (HIGH)
- NVD weakness
- CWE-416
- Published to NVD
- NVD last modified
Affected configurations (CPE)
| Product | Vulnerable versions |
|---|---|
| 365 apps (x64) | all listed versions |
| 365 apps (x86) | all listed versions |
| office 2016 (x64) | all listed versions |
| office 2016 (x86) | all listed versions |
| office 2019 (x64) | all listed versions |
| office 2019 (x86) | all listed versions |
| office long term servicing channel 2021 (x64) | all listed versions |
| office long term servicing channel 2021 (x86) | all listed versions |
| office long term servicing channel 2021 | all listed versions |
| office long term servicing channel 2024 (x64) | all listed versions |
| office long term servicing channel 2024 (x86) | all listed versions |
| office long term servicing channel 2024 | all listed versions |
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40358 (Vendor Advisory)
Acknowledgments
- Anonymous
Revision history
| Version | Date | Description |
|---|---|---|
| 1.0 | Information published. |