# CVE-2026-40410: Microsoft Windows SMB Client use after free privilege escalation

Source: https://junglewise.ai/threats/cve-2026-40410-microsoft-windows-smb-client-use-after-free-privilege-escalation  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-12. Updated: 2026-05-14  
License: CC BY 4.0 with a link back

CVE-2026-40410 · Severity: high · CVSS 7 · Published 2026-05-12

A security vulnerability exists in the Windows SMB Client, a component used by Windows computers to connect to file shares and printers over a network. An attacker who already has basic access to a system could exploit this flaw to gain full administrative control. This could allow them to steal sensitive data, install malicious software, or disrupt business operations on the affected machine.

Technologies: [Microsoft Windows SMB Client](https://junglewise.ai/threats/technologies/windows-smb-client). Vendors: [Microsoft](https://junglewise.ai/threats/vendors/microsoft).

## Quick answers

**Is CVE-2026-40410 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-40410 being exploited in the wild.

**How severe is CVE-2026-40410?** High severity, with a CVSS score of 7, published 12 May 2026.

**Which products and versions are affected?** Microsoft Windows SMB Client.

**Is there a fix for CVE-2026-40410?** 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-2026-40410 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-40410?** Check whether you run Microsoft Windows SMB Client. 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 use-after-free vulnerability (CWE-416) exists within the Microsoft Windows SMB Client driver. The flaw is triggered when the system incorrectly manages memory objects during SMB communication, allowing an attacker to reuse a memory pointer after it has been freed. To exploit this, an attacker must first have local access to the system with low-level privileges. Successful exploitation allows the attacker to execute arbitrary code with elevated system privileges. Microsoft has assigned a CVSS score of 7.0, noting high complexity for successful exploitation.

## Affected products

- Microsoft Windows SMB Client

## Timeline

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

## References

- [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40410](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40410)

## Related threats

- [Windows SMB Client privilege escalation via untrusted pointer dereference](https://junglewise.ai/threats/cve-2026-119870-untrusted-pointer-dereference-in-windows-smb-client-allows-an)
- [Windows SMB Client heap-based buffer overflow](https://junglewise.ai/threats/cve-2026-112971-heap-based-buffer-overflow-in-windows-smb-client-allows-an)
- [Microsoft Windows SMB Client use-after-free remote code execution](https://junglewise.ai/threats/cve-2026-72936-microsoft-windows-smb-client-use-after-free-remote-code-execution)
- [Microsoft Windows SMB Client out-of-bounds read](https://junglewise.ai/threats/cve-2026-69618-microsoft-windows-smb-client-out-of-bounds-read)
- [Microsoft Windows SMB Client buffer over-read](https://junglewise.ai/threats/cve-2026-65794-microsoft-windows-smb-client-buffer-over-read)