Microsoft Windows Privilege Common Log File System (CLFS) Escalation Vulnerability

An elevation of privilege vulnerability exists when the Windows Common Log File System (CLFS) driver improperly handles objects in memory, aka 'Windows Common Log File System Driver Elevation of Privilege Vulnerability'.

CheckOps priority index

4.4/10 Patch within 7 days

Severity7.8

Probability0.1

Exploitation2/5

Severity = CVSS. Probability = EPSS (FIRST). Exploitation = public signals: KEV, EUVD, ransomware, EPSS above 10 %, no account required.

EPSS · today 1.4% higher than 72.8% of CVEs

CVSS 3.1 7.8 AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:

Exploited for 1,827 days 03 Nov 2021

CISA due date 03 May 2022 for US federal agencies

Exploitation probability EPSS · FIRST

EPSS probability (%)Percentile among all CVEs

Exploitation signals 2 / 5

KEV catalog (CISA)03 Nov 2021
Exploited in EUVD (ENISA)03 Nov 2021
Used by ransomwareno
EPSS above 10 %1.4%
No account, over the networkno

What to do

Fix

Apply the vendor’s fix as soon as it is available.

CISA guidance: Apply updates per vendor instructions.

Meanwhile

Take the service off the internet or restrict access to it, watch the logs and look for signs of compromise.

Manufacturers (CRA)

Exploited vulnerability in your product: early warning to ENISA within 24 h, then notification within 72 h (Article 14 of the Cyber Resilience Act). The CRA explained

Affected products

Windows ServerWindowsWindows Server, version 1903 (Server Core installation)Windows 10 Version 1903 for 32-bit SystemsWindows 10 Version 1903 for ARM64-based SystemsWindows 10 Version 1903 for x64-based Systems

Affected versions

2008 for x64-based Systems Service Pack 2 (Core installation)
2019
10 Version 1709 for ARM64-based Systems
10 for 32-bit Systems
10 for x64-based Systems
unspecified
2008 for 32-bit Systems Service Pack 2
10 Version 1809 for ARM64-based Systems
10 Version 1809 for x64-based Systems
2016 (Core installation)
RT 8.1
10 Version 1803 for 32-bit Systems

Open source packages OSV

Affected libraries according to OSV, with fixed versions.

Timeline

11 Sept 2019
Published
03 Nov 2021
Exploitation reported (ENISA)
03 Nov 2021
Added to the KEV catalog
03 May 2022
CISA remediation due date

References

Other exploited vulnerabilities from the same vendor

CVE-2026-96951Microsoft Windows Command Injection Vulnerability
5.6 · Actively exploited
CVE-2026-65660Microsoft SharePoint Code Injection Vulnerability
5.0 · Actively exploited
CVE-2026-85880Microsoft Windows Heap-Based Buffer Overflow Vulnerability
4.3 · Actively exploited
CVE-2026-81963Microsoft Windows Link Following Vulnerability
4.3 · Actively exploited
CVE-2019-1068Microsoft SQL Server Remote Code Execution Vulnerability
7.0 · Actively exploited
CVE-2026-69836Microsoft Entra
5.3 · Actively exploited