How severe is CVE-2021-36955?

CVE-2021-36955 has a CVSS score of 7.8/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-36955?

Affected package information for CVE-2021-36955 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2021-36955?

No fixed version has been published for CVE-2021-36955 yet. Monitor the advisory for updates, apply mitigations recommended by the vendor, and use O3 Security to track when a fix becomes available in your stack.

Is CVE-2021-36955 actively exploited in the wild?

Yes. There are 3 known exploit references for CVE-2021-36955, including 2 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-36955?

CVE-2021-36955 has an EPSS (Exploit Prediction Scoring System) score of 20.7%, placing it in the 96th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score warrants monitoring and prompt remediation.

Is CVE-2021-36955 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2021-36955 (Microsoft Windows Common Log File System (CLFS) Driver Privilege Escalation Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2021-11-03. CISA required all US federal civilian agencies to remediate this vulnerability by 2021-11-17. The required action was: Apply updates per vendor instructions. This CVE has been used in known ransomware campaigns. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

Which products and versions are affected by CVE-2021-36955?

CVE-2021-36955 affects microsoft windows 7; microsoft windows 8.1; microsoft windows 10 20h2; microsoft windows 10 21h1, and 13 more product(s). Check the affected-products list on this page against your deployed version to confirm exposure.

When was CVE-2021-36955 published, and has it been updated?

CVE-2021-36955 was published on September 15, 2021 and was last updated on October 30, 2025. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CISA KEV·Added 2021-11-03 — agencies required to remediate by 2021-11-17 · Ransomware

CVE-2021-36955

HIGH

Windows Common Log File System Driver Elevation of Privilege Vulnerability

Published

Sep 15, 2021

Updated

Oct 30, 2025

Affected

0 pkgs

Patched

None yet

Exploits

3 known

EPSS Exploitation Probability

via FIRST.org ↗

20.7%probability of exploitation in next 30 days

Moderate Risk96th percentile0.00%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Description

Windows Common Log File System Driver Elevation of Privilege Vulnerability

Affected Products

17 products · 19 configurations

windows 7microsoft

all

windows 8.1microsoft

all

windows 10 20h2microsoft

< 10.0.19042.1237

range

windows 10 21h1microsoft

< 10.0.19043.1237

range

windows 10 1507microsoft

< 10.0.10240.19060

range

windows 10 1607microsoft

< 10.0.14393.4651

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

Windows Common Log File System Driver Elevation of Privilege Vulnerabili…

cisa.govCISANov 2021

Windows Common Log File System Driver Elevation of Privilege Vulnerabili…

github.comGithubJul 2022

Frequently Asked Questions

Windows Common Log File System Driver Elevation of Privilege Vulnerability

O3 Security · Impact-Aware SCA

Is CVE-2021-36955 in your stack?

O3 detects CVE-2021-36955 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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