CVE-2021-3394Public exploit

SYSTEM privilege escalation via writable service binaries

Published Feb 9, 2021 · Updated Aug 3, 2024

Incorrect permissions in Millennium Millewin 13.39.028, 13.39.28.3342, and 13.39.146.1 allow local users to gain SYSTEM privileges. The Millewin installation directory grants Users and Everyone full control, permitting replacement of executables launched by MillewinTaskService, PDS Server, or MilleLiveUpdate. Low-privileged access to the Windows host is required; a substituted file executes as SYSTEM when an affected service starts or the application launches after reboot.

CVSS severity8.8
High
EPSS probability5.79%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect permissions in Millennium Millewin 13.39.028, 13.39.28.3342, and 13.39.146.1 allow local users to gain SYSTEM privileges. The Millewin installation directory grants Users and Everyone full control, permitting replacement of executables launched by MillewinTaskService, PDS Server, or MilleLiveUpdate. Low-privileged access to the Windows host is required; a substituted file executes as SYSTEM when an affected service starts or the application launches after reboot.

The record

CVE
CVE-2021-3394
Published
Feb 9, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-276, T1574.010
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 9, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

8.8NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
6.5NVDAV:N/AC:L/Au:S/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-276Incorrect Default Permissions
T1574.010Hijack Execution Flow: Services File Permissions Weakness

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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