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Vulnerabilities

Vulnerability · CVE-2026-66804

ZDI-26-617: Microsoft Windows MIDI Service Incorrect Permission Assignment Local Privilege Escalation Vulnerability

Published Sep 8, 2026 · ZDI-26-617: Microsoft Windows MIDI

Check if you run it

No confirmed exploitation is on record for CVE-2026-66804. EPSS is 0.30%. Act only if a listed version of ZDI-26-617: Microsoft Windows MIDI is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (ZDI-26-617: Microsoft Windows MIDI).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High7.8
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.30%
Remediation
Not established
Affected products
See sources for product scope

Research mention from Google Project Zero. This is not vendor confirmation or proof of exploitation. This short blog post is about abusing a privilege escalation bug that Microsoft recently fixed in Windows, CVE-2026-66804, that I and 14 others reported. This issue is an incomplete fix for CVE-2026-50343, a bug dubbed “Dark Elevator” by Calif. The root cause of the bug was a dangling COM object registration for the CrossDevice COM object with the CLSID {E9F83CF2-E0C0-4CA7-AF01-E90C70BEF496}. A COM registration typically needs two parts: a server executable, which for in-process components is a DLL and a CLSID entry under the HKEY_CLASSES_ROOT registry key which points to that DLL.

No affected version ranges are stored yet. Use the vendor advisory before you decide this record does not apply.

How to fix CVE-2026-66804

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-66804. EPSS is 0.30%. Act only if a listed version of ZDI-26-617: Microsoft Windows MIDI is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.30%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Technology hubs

Windows security

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Sep 8, 2026 · Catalog

    Detected

    This vulnerability allows local attackers to escalate privileges on affected installations of Microsoft Windows. An attacker must first obtain the ability to execute low-privileged code on the target system in order to exploit this vulnerability. The ZDI has assigned a CVSS rating of 7.8. The following CVEs are assigned: CVE-2026-66804.

Sources

  • CVE.orgVulnerability recordCVE-2026-66804

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-66804

    30-day exploitation probability 0.3%

    first.org
  • Google Project ZeroThreat researchCVE-2026-66804

    Research mention from Google Project Zero. Not confirmation of exploitation.

    projectzero.google
  • Zero Day InitiativeCoordinated disclosureZDI-26-617

    This vulnerability allows local attackers to escalate privileges on affected installations of Microsoft Windows. An attacker must first obtain the ability to execute low-privileged code on the target system in order to exploit this vulnerability. The ZDI has assigned a CVSS rating of 7.8. The following CVEs are assigned: CVE-2026-66804.

    zerodayinitiative.com

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.