CVE-2021-36955
published 2021-09-15CVE-2021-36955: Windows Common Log File System Driver Elevation of Privilege Vulnerability
PriorityP185high7.8CVSS 3.1
AVLACLPRLUINSUCHIHAH
KEVITWEXPLOITRansomware
CISA Known Exploited Vulnerabilitydue 2021-11-17
Exploited in the wild
EPSS
3.23%
86.9th percentile
Windows Common Log File System Driver Elevation of Privilege Vulnerability
Affected
49 ranges· showing 25
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| microsoft | windows_10_1507 | < 10.0.10240.19060 | 10.0.10240.19060 |
| microsoft | windows_10_1607 | < 10.0.14393.4651 | 10.0.14393.4651 |
| microsoft | windows_10_1809 | < 10.0.17763.2183 | 10.0.17763.2183 |
| microsoft | windows_10_1909 | < 10.0.18363.1801 | 10.0.18363.1801 |
| microsoft | windows_10_2004 | < 10.0.19041.1237 | 10.0.19041.1237 |
| microsoft | windows_10_20h2 | < 10.0.19042.1237 | 10.0.19042.1237 |
| microsoft | windows_10_21h1 | < 10.0.19043.1237 | 10.0.19043.1237 |
| microsoft | windows_10_version_1507 | >= 10.0.0 < 10.0.10240.19060 | 10.0.10240.19060 |
| microsoft | windows_10_version_1607 | >= 10.0.0 < 10.0.14393.4651 | 10.0.14393.4651 |
| microsoft | windows_10_version_1809 | >= 10.0.0 < 10.0.17763.2183 | 10.0.17763.2183 |
| microsoft | windows_10_version_1909 | >= 10.0.0 < 10.0.18363.1801 | 10.0.18363.1801 |
| microsoft | windows_10_version_2004 | >= 10.0.0 < 10.0.19041.1237 | 10.0.19041.1237 |
| microsoft | windows_10_version_20h2 | >= 10.0.0 < 10.0.19042.1237 | 10.0.19042.1237 |
| microsoft | windows_10_version_21h1 | >= 10.0.0 < 10.0.19043.1237 | 10.0.19043.1237 |
| microsoft | windows_7 | >= 6.1.0 < 6.1.7601.25712 | 6.1.7601.25712 |
| microsoft | windows_7_service_pack_1 | >= 6.1.0 < 6.1.7601.25712 | 6.1.7601.25712 |
| microsoft | windows_8.1 | >= 6.3.0 < 6.3.9600.20120 | 6.3.9600.20120 |
| microsoft | windows_server_2004 | < 10.0.19041.1237 | 10.0.19041.1237 |
| microsoft | windows_server_2008 | — | — |
| microsoft | windows_server_2008_r2_service_pack_1 | >= 6.0.0 < 6.1.7601.25712 | 6.1.7601.25712 |
| microsoft | windows_server_2008_r2_service_pack_1 | >= 6.1.0 < 6.1.7601.25712 | 6.1.7601.25712 |
| microsoft | windows_server_2008_service_pack_2 | >= 6.0.0 < 6.0.6003.21218 | 6.0.6003.21218 |
| microsoft | windows_server_2012 | >= 6.2.0 < 6.2.9200.23462 | 6.2.9200.23462 |
| microsoft | windows_server_2012_r2 | >= 6.3.0 < 6.3.9600.20120 | 6.3.9600.20120 |
| microsoft | windows_server_2016 | < 10.0.14393.4651 | 10.0.14393.4651 |
Detection & IOCsextracted from sources · hover to see the quote
- →CVE-2021-36955 targets the Windows Common Log File System (CLFS) Driver and results in privilege escalation; monitor for unexpected privilege elevation via clfs.sys interactions. ↗
- →The vulnerability affects a wide range of Windows OS versions from Windows 7 SP1 through Windows Server 2022; prioritize detection on older, unpatched endpoints. ↗
- →Microsoft rates exploitation as 'More Likely' for both latest and older software releases; treat any CLFS driver anomaly on unpatched systems as high-priority. ↗
- ·No public exploit code or active in-the-wild exploitation was confirmed at time of advisory; Microsoft marked it as 'Publicly Disclosed: No' and 'Exploited: No', though exploitation was rated as 'More Likely'. ↗
CVSS provenance
nvdv3.17.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
nvdv2.04.6MEDIUMAV:L/AC:L/Au:N/C:P/I:P/A:P
vulncheck7.8HIGH
cisa7.8HIGH
vendor_msrc7.8HIGH
CVEs like this are exactly what “Exploited This Week” covers.
Every Monday: what got weaponized or added to CISA KEV in the last seven days — each CVE cross-linked to its PoC, Nuclei template, and detection rule. Free, one email a week, unsubscribe in one click.
GHSA
GHSA-g26f-6mx8-j24w: Windows Common Log File System Driver Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-36963, CVE-2021-38633
ghsa_unreviewed·2022-05-24·CVSS 7.8
CVE-2021-36955 [HIGH] CWE-269 GHSA-g26f-6mx8-j24w: Windows Common Log File System Driver Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-36963, CVE-2021-38633
Windows Common Log File System Driver Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-36963, CVE-2021-38633.
GHSA
GHSA-jwrp-9w74-vqmj: Windows Common Log File System Driver Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-36955, CVE-2021-38633
ghsa_unreviewed·2022-05-24·CVSS 7.8
CVE-2021-36963 [HIGH] CWE-269 GHSA-jwrp-9w74-vqmj: Windows Common Log File System Driver Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-36955, CVE-2021-38633
Windows Common Log File System Driver Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-36955, CVE-2021-38633.
GHSA
GHSA-f76r-r2wm-fmpj: Windows Common Log File System Driver Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-36955, CVE-2021-36963
ghsa_unreviewed·2022-05-24·CVSS 7.8
CVE-2021-38633 [HIGH] CWE-269 GHSA-f76r-r2wm-fmpj: Windows Common Log File System Driver Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-36955, CVE-2021-36963
Windows Common Log File System Driver Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-36955, CVE-2021-36963.
VulnCheck
Microsoft Windows Common Log File System (CLFS) Driver Privilege Escalation Vulnerability
vulncheck·2021·CVSS 7.8
CVE-2021-36955 [HIGH] Microsoft Windows Common Log File System (CLFS) Driver Privilege Escalation Vulnerability
Microsoft Windows Common Log File System (CLFS) Driver Privilege Escalation Vulnerability
Microsoft Windows Common Log File System (CLFS) driver contains an unspecified vulnerability that allows for privilege escalation.
Affected: Microsoft Windows
Required Action: Apply updates per vendor instructions.
Known Ransomware Campaign Use: Known
Exploitation References: https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json; https://mp.weixin.qq.com/s?__biz=Mzg2NjgzNjA5NQ==&mid=2247514973&idx=2&sn=0776f8f83c032c4d7433a567270a7ee1&source=41#wechat_redirect; https://www.cisa.gov/sites/default/files/2024-07/aa24-207a-dprk-cyber-group-conducts-global-espionage-campaign.pdf; https://ctrlaltint3l.github.io/threat%20research/china-vietnam-campaign/
Exploit PoC: https:
CISA
Microsoft Windows Common Log File System (CLFS) Driver Privilege Escalation Vulnerability
cisa·2021-11-03·CVSS 7.8
CVE-2021-36955 [HIGH] Microsoft Windows Common Log File System (CLFS) Driver Privilege Escalation Vulnerability
Vulnerability: Microsoft Windows Common Log File System (CLFS) Driver Privilege Escalation Vulnerability
Affected: Microsoft Windows
Microsoft Windows Common Log File System (CLFS) driver contains an unspecified vulnerability that allows for privilege escalation.
Required Action: Apply updates per vendor instructions.
Notes: https://nvd.nist.gov/vuln/detail/CVE-2021-36955
Remediation Due Date: 2021-11-17
Microsoft
Windows Common Log File System Driver Elevation of Privilege Vulnerability
vendor_msrc·2021-09-14·CVSS 7.8
CVE-2021-36955 [HIGH] Windows Common Log File System Driver Elevation of Privilege Vulnerability
Windows Common Log File System Driver Elevation of Privilege Vulnerability
Windows Common Log File System Driver: Windows Common Log File System Driver
Microsoft: Microsoft
Impact: Elevation of Privilege
Exploit Status: Publicly Disclosed:No;Exploited:No;Latest Software Release:Exploitation More Likely;Older Software Release:Exploitation More Likely;DOS:N/A
Reference: https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5005568
Reference: https://support.microsoft.com/help/5005568
Reference: https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5005566
Reference: https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5005565
Reference: https://support.microsoft.com/help/5005565
Reference: https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5005575
R
No detection rules found.
No public exploits indexed.
Securelist
Windows CLFS and five exploits used by ransomware operators (Exploit #4 – CVE-2023-23376)
blogs_securelist·2023-12-21·CVSS 7.8
[HIGH] Windows CLFS and five exploits used by ransomware operators (Exploit #4 – CVE-2023-23376)
Authors
Boris Larin
This is part five of our study about the Common Log File System (CLFS) and five vulnerabilities in this Windows OS component that have been used in ransomware attacks throughout the year. Please read the previous parts first if you haven’t already.
You can skip to the other parts using this table of contents or using the link at the end of this part.
Part 1 – Windows CLFS and five exploits of ransomware operators
Part 2 – Windows CLFS and five exploits of ransomware operators (Exploit #1 – CVE-2022-24521)
Part 3 – Windows CLFS and five exploits of ransomware operators (Exploit #2 – September 2022)
Part 4 – Windows CLFS and five exploits of ransomware operators (Exploit #3 – October 2022)
Part 5 – Windows CLFS and five exploits of ransomware operators (Exploit #4
Securelist
Windows CLFS and five exploits used by ransomware operators (Exploit #4 – CVE-2023-23376)
blogs_securelist·2023-12-21·CVSS 7.8
CVE-2023-23376 [HIGH] Windows CLFS and five exploits used by ransomware operators (Exploit #4 – CVE-2023-23376)
Authors
- Boris Larin
This is part five of our study about the Common Log File System (CLFS) and five vulnerabilities in this Windows OS component that have been used in ransomware attacks throughout the year. Please read the previous parts first if you haven’t already.
You can skip to the other parts using this table of contents or using the link at the end of this part.
- Part 1 – Windows CLFS and five exploits of ransomware operators
- Part 2 – Windows CLFS and five exploits of ransomware operators (Exploit #1 – CVE-2022-24521)
- Part 3 – Windows CLFS and five exploits of ransomware operators (Exploit #2 – September 2022)
- Part 4 – Windows CLFS and five exploits of ransomware operators (Exploit #3 – October 2022)
- Part 5 – Windows CLFS and five exploits of ransomware operators (Ex
Qualys
Managing CISA Known Exploited Vulnerabilities with Qualys VMDR | Qualys
blogs_qualys·2022-02-23
Managing CISA Known Exploited Vulnerabilities with Qualys VMDR | Qualys
#### Table of Contents
- Situation
- Directive Scope
- CISA Catalog of Known Exploited Vulnerabilities
- Detect CISA Vulnerabilities Using Qualys VMDR
- CISA Exploited RTI
- Detailed Operational Dashboard
- Remediation
- Federal Enterprises and Agencies Can Act Now
- Summary
- Getting Started
CISA released a directive in November 2021, recommending urgent and prioritized remediation of actively exploited vulnerabilities. Both government agencies and corporations should heed this advice. This blog outlines how Qualys Vulnerability Management, Detection & Response can be used by any organization to respond to this directive efficiently and effectively.
## Situation
Last November 2021, the U.S. Cybersecurity and Infrastructure Security Agency (CISA) released a Binding Operational Directiv
Qualys
Qualys Response to CISA Alert: Binding Operational Directive 22-01
blogs_qualys·2021-11-09
Qualys Response to CISA Alert: Binding Operational Directive 22-01
## Table of Contents
Overview
Directive Scope
CISA Catalog of Known Exploited Vulnerabilities
Detect CISAs Vulnerabilities Using Qualys VMDR
Remediation
Federal Enterprises and Agencies Can Act Now
Summary
Getting Started
Start your VMDR 30-day, no-cost trial today
## Overview
On November 3, 2021, the U.S. Cybersecurity and Infrastructure Security Agency (CISA) released a Binding Operational Directive 22-01 , “Reducing the Significant Risk of Known Exploited Vulnerabilities.” This directive recommends urgent and prioritized remediation of the vulnerabilities that adversaries are actively exploiting. It establishes a CISA-managed catalog of known exploited vulnerabilities that carry significant risk to the federal government and establishes requirements for agencies to remediate
Qualys
Qualys Response to CISA Alert: Binding Operational Directive 22-01 | Qualys
blogs_qualys·2021-11-09
Qualys Response to CISA Alert: Binding Operational Directive 22-01 | Qualys
#### Table of Contents
- Overview
- Directive Scope
- CISA Catalog of Known Exploited Vulnerabilities
- Detect CISAs Vulnerabilities Using Qualys VMDR
- Remediation
- Federal Enterprises and Agencies Can Act Now
- Summary
- Getting Started
Start your VMDR 30-day, no-cost trial today
## Overview
On November 3, 2021, the U.S. Cybersecurity and Infrastructure Security Agency (CISA) released a Binding Operational Directive 22-01, “Reducing the Significant Risk of Known Exploited Vulnerabilities.” This directive recommends urgent and prioritized remediation of the vulnerabilities that adversaries are actively exploiting. It establishes a CISA-managed catalog of known exploited vulnerabilities that carry significant risk to the federal government and establishes requirements for agencies to
Qualys
Microsoft and Adobe Patch Tuesday (September 2021) – Microsoft 60 Vulnerabilities with 3 Critical, Adobe 61 Vulnerabilities
blogs_qualys·2021-09-14·CVSS 8.1
CVE-2021-40444 [HIGH] Microsoft and Adobe Patch Tuesday (September 2021) – Microsoft 60 Vulnerabilities with 3 Critical, Adobe 61 Vulnerabilities
## Microsoft Patch Tuesday – September 2021
Microsoft patched 60 vulnerabilities in their September 2021 Patch Tuesday release, and an additional 26 CVEs since September 1st. Among the 60 released in the September Patch Tuesday, 3 of them are rated as critical severity, one as moderate, and 56 as important.
## Critical Microsoft Vulnerabilities Patched
CVE-2021-40444 – Microsoft MSHTML Remote Code Execution Vulnerability
This vulnerability has been publicly disclosed and is known to be exploited. The vulnerability allows for remote code execution via MSHTML, a component used by Internet Explorer and Office. Microsoft also released a workaround to show how users can disable ActiveX controls in IE. The vendor has assigned a CVSSv3 base score of 8.8. It should be prioritized for patching.
Talos
Microsoft Patch Tuesday for Sept. 2021 — Snort rules and prominent vulnerabilities
blogs_talos·2021-09-14·CVSS 8.1
CVE-2021-40444 [HIGH] Microsoft Patch Tuesday for Sept. 2021 — Snort rules and prominent vulnerabilities
By Jon Munshaw, with contributions from Holger Unterbrink.
Microsoft released its monthly security update Tuesday, disclosing 85 vulnerabilities across the company’s firmware and software. This month’s release is headlined by an official patch for the critical remote code execution vulnerability disclosed earlier this month in MSHTML.
CVE-2021-40444 is being actively exploited in the wild, according to Microsoft, and proof-of-concept code is now available, potentially widening the potential for attacks exploiting this vulnerability. This is the first official Microsoft update to address this issue. Talos has additional protection available here.
Users should download this patch immediately. Additionally, they can disable the installation of all ActiveX controls in Internet Explorer to m
Talos
Microsoft Patch Tuesday for Sept. 2021 — Snort rules and prominent vulnerabilities
blogs_talos·2021-09-14·CVSS 8.1
CVE-2021-40444 [HIGH] Microsoft Patch Tuesday for Sept. 2021 — Snort rules and prominent vulnerabilities
## Microsoft Patch Tuesday for Sept. 2021 — Snort rules and prominent vulnerabilities
By Jon Munshaw, with contributions from Holger Unterbrink.
Microsoft released its monthly security update Tuesday, disclosing 85 vulnerabilities across the company’s firmware and software. This month’s release is headlined by an official patch for the critical remote code execution vulnerability disclosed earlier this month in MSHTML .
CVE-2021-40444 is being actively exploited in the wild, according to Microsoft, and proof-of-concept code is now available, potentially widening the potential for attacks exploiting this vulnerability. This is the first official Microsoft update to address this issue. Talos has additional protection available here .
Users should download this patch immediately. Addition
Tenable
Microsoft’s September 2021 Patch Tuesday Addresses 60 CVEs (CVE-2021-40444)
blogs_tenable·2021-09-14·CVSS 8.8
[HIGH] Microsoft’s September 2021 Patch Tuesday Addresses 60 CVEs (CVE-2021-40444)
## Cloud Exposure
Tenable Cloud Security (CNAPP) Request a demo
Tenable Cloud Vulnerability Management Request a demo
Tenable CIEM Request a demo
Secure your cloud
## Vulnerability Exposure
Tenable Vulnerability Management Try for free
Tenable Security Center Request a demo
Tenable Web App Scanning Try for free
Tenable Patch Management Request a demo
Tenable Enclave Security Request a demo
Tenable Attack Surface Management Request a demo
Tenable Nessus Try for free
## AI Exposure
Tenable AI Exposure Request a demo
## OT/IoT Exposure
Tenable OT Security Request a demo
## Identity Exposure
Tenable Identity Exposure Request a demo
## Business needs
Active Directory
AI Security Posture Management (AI-SPM)
AWS security
Azure security
Cloud Security Posture Man
Crowdstrike
September 2021 Patch Tuesday: Updates and Analysis
blogs_crowdstrike·CVSS 7.5
CVE-2026-20929 [HIGH] September 2021 Patch Tuesday: Updates and Analysis
STARDUST CHOLLIMA Likely Compromises Axios npm Package Apr 01, 2026
Falcon for IT Supports Windows Secure Boot Certificate Lifecycle Management Apr 01, 2026
Detecting CVE-2026-20929: Kerberos Authentication Relay via CNAME Abuse Mar 31, 2026
How Charlotte AI AgentWorks Fuels Security's Agentic Ecosystem Mar 25, 2026
STARDUST CHOLLIMA Likely Compromises Axios npm Package Apr 01, 2026
Falcon for IT Supports Windows Secure Boot Certificate Lifecycle Management Apr 01, 2026
Detecting CVE-2026-20929: Kerberos Authentication Relay via CNAME Abuse Mar 31, 2026
How Charlotte AI AgentWorks Fuels Security's Agentic Ecosystem Mar 25, 2026
Video Highlights the 4 Key Steps to Successful Incident Response Dec 02, 2019
Helping Non-Security Stakeholders Understand ATT&CK in 10 Minutes or Less [VI
Zscaler
Zscaler protects against Windows vulnerability | 09-14-2021
blogs_zscaler·CVSS 7.8
[HIGH] Zscaler protects against Windows vulnerability | 09-14-2021
Provide users with seamless, secure, reliable access to applications and data.
Build and run secure cloud apps, enable zero trust cloud connectivity, and protect workloads from data center to cloud.
Provide zero trust connectivity for IoT and OT devices and secure remote access to OT systems.
Provide zero trust site-to-site connectivity and reliable access to B2B apps for partners.
Industry Report
Zscaler: A Leader in the 2025 Gartner® Magic Quadrant™ for Security Service Edge (SSE)
USE CASES
INDUSTRY & MARKET SOLUTIONS
PARTNERS
TECHNOLOGY PARTNERS
Resource Center
Events & Trainings
Security Research & Services
Tools
Community & Support
CXO REVOLUTIONARIES
Amplifying the voices of real-world digital and zero trust pioneers
Discover how it began and where it’s going
Meet o
2021-09-15
Published
2021-11-03
Added to CISA KEV
Exploited in the wild