# CVE-2026-40420: Microsoft Office Click-to-Run improper access control privilege escalation

Source: https://junglewise.ai/threats/cve-2026-40420-microsoft-office-click-to-run-improper-access-control-privilege  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-12. Updated: 2026-05-19  
License: CC BY 4.0 with a link back

CVE-2026-40420 · Severity: high · CVSS 8.8 · Published 2026-05-12

A security vulnerability in the Microsoft Office installation and update service could allow a user with limited access to gain full administrative control over a computer. This component is responsible for managing how Office applications are installed and kept up to date on Windows systems. If exploited, an attacker who already has a basic account on the machine could bypass security restrictions to access sensitive data or install malicious software.

Technologies: [Microsoft Office Click-to-Run](https://junglewise.ai/threats/technologies/office-click-to-run). Vendors: [Microsoft](https://junglewise.ai/threats/vendors/microsoft).

## Quick answers

**Is CVE-2026-40420 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-40420 being exploited in the wild.

**How severe is CVE-2026-40420?** High severity, with a CVSS score of 8.8, published 12 May 2026.

**Which products and versions are affected?** Microsoft Office Click-to-Run (C2R).

**Is there a fix for CVE-2026-40420?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-40420 attacked?** It is attacked with local access, in a network appliance.

**Am I affected by CVE-2026-40420?** Check whether you run Microsoft Office Click-to-Run. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A local privilege escalation vulnerability exists in the Microsoft Office Click-to-Run (C2R) service due to improper access control (CWE-284). An attacker with low-privileged local access can exploit this flaw to execute code with higher privileges, potentially reaching SYSTEM level. The vulnerability is characterized by a CVSS 3.1 score of 8.8, notably featuring a Scope change (S:C), indicating the impact extends beyond the immediate security scope of the Office component. No user interaction is required for exploitation. Microsoft has released security updates to address this issue via the MSRC.

## Affected products

- Microsoft Office Click-to-Run (C2R)

## Timeline

- 2026-05-12: disclosed
- 2026-05-12: advisory

## References

- [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40420](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40420)

## Related threats

- [Microsoft Office Click-to-Run privilege escalation via use-after-free](https://junglewise.ai/threats/cve-2026-47293-microsoft-office-click-to-run-privilege-escalation-via-use-after)
- [Microsoft Office Click-to-Run use after free privilege escalation](https://junglewise.ai/threats/cve-2026-40418-microsoft-office-click-to-run-use-after-free-privilege-escalation)
- [Microsoft Office Click-to-Run privilege escalation](https://junglewise.ai/threats/cve-2026-35436-microsoft-office-click-to-run-privilege-escalation)