CriticalCVE-2023-28252

Windows Common Log File System Driver Elevation of Privilege Vulnerability (CVE-2023-28252)

Published 11.04.2023In CISA KEV since 11.04.2023Sources: CVE.org, pwn.watch, SingCERT

What is affected, what to do

Windows Common Log File System Driver Elevation of Privilege Vulnerability

The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update Microsoft Windows 10 Version 1809 to version 10.0.17763.4252, Microsoft Windows Server 2019 to version 10.0.17763.4252, Microsoft Windows Server 2019 (Server Core installation) to version 10.0.17763.4252. Immediate actions, mitigation and detection rules are in the runbook below.

Affected: Microsoft Windows 10 Version 1809 lt 10.0.17763.0..10.0.17763.4252
Microsoft Windows Server 2019 lt 10.0.17763.0..10.0.17763.4252
Microsoft Windows Server 2019 (Server Core installation) lt 10.0.17763.0..10.0.17763.4252
Microsoft Windows Server 2022 lt 10.0.20348.0..10.0.20348.1668
Microsoft Windows 10 Version 20H2 lt 10.0.0..10.0.19042.2846
Microsoft Windows 11 version 21H2 lt 10.0.0..10.0.22000.1817
Microsoft Windows 10 Version 21H2 lt 10.0.19043.0..10.0.19044.2846
Microsoft Windows 11 version 22H2 lt 10.0.22621.0..10.0.22621.1555
Microsoft Windows 10 Version 22H2 lt 10.0.19045.0..10.0.19045.2846
Microsoft Windows 10 Version 1507 lt 10.0.10240.0..10.0.10240.19869
Microsoft Windows 10 Version 1607 lt 10.0.14393.0..10.0.14393.5850
Microsoft Windows Server 2016 lt 10.0.14393.0..10.0.14393.5850
Microsoft Windows Server 2016 (Server Core installation) lt 10.0.14393.0..10.0.14393.5850
Microsoft Windows Server 2008 Service Pack 2 lt 6.0.6003.0..6.0.6003.22015
Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) lt 6.0.6003.0..6.0.6003.22015
Microsoft Windows Server 2008 R2 Service Pack 1 lt 6.1.7601.0..6.1.7601.26466
Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) lt 6.1.7601.0..6.1.7601.26466
Microsoft Windows Server 2012 lt 6.2.9200.0..6.2.9200.24216
Microsoft Windows Server 2012 (Server Core installation) lt 6.2.9200.0..6.2.9200.24216
Microsoft Windows Server 2012 R2 lt 6.3.9600.0..6.3.9600.20919
Microsoft Windows Server 2012 R2 (Server Core installation) lt 6.3.9600.0..6.3.9600.20919
Fixed in: Microsoft Windows 10 Version 1809 10.0.17763.4252
Microsoft Windows Server 2019 10.0.17763.4252
Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.4252
Microsoft Windows Server 2022 10.0.20348.1668
Microsoft Windows 10 Version 20H2 10.0.19042.2846
Microsoft Windows 11 version 21H2 10.0.22000.1817
Microsoft Windows 10 Version 21H2 10.0.19044.2846
Microsoft Windows 11 version 22H2 10.0.22621.1555
Microsoft Windows 10 Version 22H2 10.0.19045.2846
Microsoft Windows 10 Version 1507 10.0.10240.19869
Microsoft Windows 10 Version 1607 10.0.14393.5850
Microsoft Windows Server 2016 10.0.14393.5850
Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.5850
Microsoft Windows Server 2008 Service Pack 2 6.0.6003.22015
Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) 6.0.6003.22015
Microsoft Windows Server 2008 R2 Service Pack 1 6.1.7601.26466
Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) 6.1.7601.26466
Microsoft Windows Server 2012 6.2.9200.24216
Microsoft Windows Server 2012 (Server Core installation) 6.2.9200.24216
Microsoft Windows Server 2012 R2 6.3.9600.20919
Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.20919

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Metrics

7.8

Priority

XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

Source: NVD, CVSS v3

7.8

CVSS v3

Severity High on the scale from 0 to 10.

Source: CVE.org, pwn.watch, SingCERT

48.9 %

EPSS score

Elevated — model estimates 10-50% exploitation likelihood.

Source: FIRST EPSS, percentile 98.9

Show all metrics

Severity: Critical
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 244.71 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: actively exploitedSource: CSA/SingCERT How we classify
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 7.8 Methodology
CVSS v3 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 7.8
EPSS score The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“. Read in glossary: 48.9 %; Elevated — model estimates 10-50% exploitation likelihood.
EPSS percentile The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking. Read in glossary: 98.9; Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: Actively exploited
Published: 11.04.2023
In CISA KEV since The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: 11.04.2023
CISA assessment (SSVC): Exploitation: active · not automatable · Technical impact: total; Source: CISA Vulnrichment, as of 30 May 2024
CWE CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect. Read in glossary: CWE-122

Response and mitigation

Why act now?

Prioritisation rationale

This is a local privilege escalation with low attack complexity. It needs only a low-privileged user context and no user interaction, which makes it the standard second stage after phishing or credential theft to gain full SYSTEM control. CISA flags it as used in ransomware campaigns, and its exploitation likelihood ranks among the highest of all known CVEs. CLFS driver bugs have also been a recurring, well-understood exploit target for years. Despite the local attack vector, organisations with large Windows client estates, RDS/VDI farms or weak initial-access controls should treat closing this gap as critical and give it top priority in the patch cycle. Any remaining unpatched or out-of-support builds should be documented as a NIS2-relevant risk.

01
Runbook step 1
Immediate response (0-24 h)
- Deploy the Microsoft April 2023 security update (Patch Tuesday, 11 April 2023) to all Windows clients. The cumulative updates carry the fix. Look up the per-build KB numbers in the Microsoft Security Update Guide entry for CVE-2023-28252. Verify builds against the reference builds in the advisory, e.g. 10.0.19045.2846 (Win10 22H2), 10.0.19044.2846 (21H2), 10.0.22621.1555 (Win11 22H2), 10.0.22000.1817 (Win11 21H2), 10.0.17763.4252 (1809), 10.0.14393.5850 (1607). Any later cumulative update also includes the fix.
- Check Windows Server editions separately. The context lists client builds only, so confirm Server applicability in the vendor advisory. Prioritise terminal servers and Citrix/RDS hosts, which carry many interactive low-privilege users.
- Inventory unpatched endpoints via Intune, SCCM/MECM or WSUS by querying the OS build or the clfs.sys/ntoskrnl.exe file version. Treat out-of-support builds (1507, 20H2) as high-risk assets and isolate or migrate them.
- Launch a retro-hunt using the detection rules below. This EoP is chained after initial access, so a hit means an attacker already has code execution on the host. In that case, isolate the host, capture memory and trigger the IR process.
- On confirmed compromise, rotate every local and domain credential cached on the affected host. SYSTEM access enables LSASS dumping.
02
Runbook step 2
Mitigation layers
- Configuration: Microsoft provides no workaround, and the CLFS driver cannot be disabled without breaking OS functionality. Patching is the only fix, so compensating controls must target the initial-access stage that precedes it.
- Endpoint hardening / application control: Use WDAC or AppLocker to block unsigned binaries from user-writable paths (%USERPROFILE%, %TEMP%, C:\Users\Public, C:\ProgramData). Exploits for this flaw are usually dropped as standalone executables in exactly those locations.
- ASR rules (Defender for Endpoint) in block mode: Enable "Block executable files from running unless they meet a prevalence, age, or trusted list criterion", "Block credential stealing from LSASS" and "Block Office applications from creating child processes". Together they break the usual access-to-escalation chain.
- IAM / least privilege: Remove local admin rights from users. Roll out Windows LAPS so that a single escalation does not yield a reusable local admin password. Enable Credential Guard and LSA protection (RunAsPPL).
- Network segmentation: Block client-to-client SMB (445/tcp), RPC (135/tcp) and WinRM (5985/5986/tcp) via host firewall policy. This contains lateral movement, which is the next step in ransomware operations after SYSTEM takeover.
- Enforce EDR tamper protection, since attackers holding SYSTEM routinely try to kill security agents.
03
Runbook step 3
Detection rules
- Sysmon EID 11 (FileCreate) for .blf files written by unusual processes: Exploits create crafted CLFS base log files, often under C:\Users\Public\ or %TEMP%. Sigma shape: TargetFilename|endswith: '.blf' AND Image|contains: ['\Users\', '\Temp\', '\ProgramData\']. Allowlist legitimate system and service consumers of CLFS.
- Privilege jump without a legitimate parent chain (Sysmon EID 1 / Security 4688): Flag any process running as NT AUTHORITY\SYSTEM with a Medium-integrity, user-context parent, such as a SYSTEM cmd.exe spawned by a binary in %TEMP%. KQL: DeviceProcessEvents | where ProcessIntegrityLevel == "System" and InitiatingProcessIntegrityLevel == "Medium" and InitiatingProcessFolderPath has_any (@"\Users\", @"\Temp\")
- Bugchecks involving clfs.sys: Failed exploit attempts crash hosts. Correlate System log Event ID 1001 (BugCheck) and Event ID 41 (Kernel-Power) on workstations, then check crash dumps for CLFS.SYS in the stack.
- Post-escalation activity: Watch for LSASS access (Sysmon EID 10, TargetImage lsass.exe, GrantedAccess 0x1010/0x1410) and for vssadmin delete shadows or wmic shadowcopy delete (4688). When these follow a .blf hit closely, ransomware staging is likely.
- Search EDR/Defender alert history for CLFS-related exploit detections. In SPL, for example: index=edr signature="*CLFS*" OR signature="*CVE-2023-28252*".

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

Windows Common Log File System Driver Elevation of Privilege Vulnerability

Source: cvelistv5, pwn.watch, NVD (NIST), CISA KEV Catalog, CVE.org (MITRE), CSA/SingCERT

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
Microsoft	Windows 10 Version 1507	`10.0.10240.0 – < 10.0.10240.19869`	`10.0.10240.19869`
Microsoft	Windows 10 Version 1607	`10.0.14393.0 – < 10.0.14393.5850`	`10.0.14393.5850`
Microsoft	Windows 10 Version 1809	`10.0.17763.0 – < 10.0.17763.4252`	`10.0.17763.4252`
Microsoft	Windows 10 Version 20H2	`10.0.0 – < 10.0.19042.2846`	`10.0.19042.2846`
Microsoft	Windows 10 Version 21H2	`10.0.19043.0 – < 10.0.19044.2846`	`10.0.19044.2846`
Microsoft	Windows 10 Version 22H2	`10.0.19045.0 – < 10.0.19045.2846`	`10.0.19045.2846`
Microsoft	Windows 11 version 21H2	`10.0.0 – < 10.0.22000.1817`	`10.0.22000.1817`
Microsoft	Windows 11 version 22H2	`10.0.22621.0 – < 10.0.22621.1555`	`10.0.22621.1555`
Microsoft	Windows Server 2008 R2 Service Pack 1	`6.1.7601.0 – < 6.1.7601.26466`	`6.1.7601.26466`
Microsoft	Windows Server 2008 R2 Service Pack 1 (Server Core installation)	`6.1.7601.0 – < 6.1.7601.26466`	`6.1.7601.26466`
Microsoft	Windows Server 2008 Service Pack 2	`6.0.6003.0 – < 6.0.6003.22015`	`6.0.6003.22015`
Microsoft	Windows Server 2008 Service Pack 2 (Server Core installation)	`6.0.6003.0 – < 6.0.6003.22015`	`6.0.6003.22015`
Microsoft	Windows Server 2012	`6.2.9200.0 – < 6.2.9200.24216`	`6.2.9200.24216`
Microsoft	Windows Server 2012 (Server Core installation)	`6.2.9200.0 – < 6.2.9200.24216`	`6.2.9200.24216`
Microsoft	Windows Server 2012 R2	`6.3.9600.0 – < 6.3.9600.20919`	`6.3.9600.20919`
Microsoft	Windows Server 2012 R2 (Server Core installation)	`6.3.9600.0 – < 6.3.9600.20919`	`6.3.9600.20919`
Microsoft	Windows Server 2016	`10.0.14393.0 – < 10.0.14393.5850`	`10.0.14393.5850`
Microsoft	Windows Server 2016 (Server Core installation)	`10.0.14393.0 – < 10.0.14393.5850`	`10.0.14393.5850`
Microsoft	Windows Server 2019	`10.0.17763.0 – < 10.0.17763.4252`	`10.0.17763.4252`
Microsoft	Windows Server 2019 (Server Core installation)	`10.0.17763.0 – < 10.0.17763.4252`	`10.0.17763.4252`
Microsoft	Windows Server 2022	`10.0.20348.0 – < 10.0.20348.1668`	`10.0.20348.1668`

Vendors and products

Affected operating systems

Affected operating systems

Windows	microsoft	windows_10_1507	—
Windows	microsoft	windows_10_1607	—
Windows	microsoft	windows_10_1809	—
Windows	microsoft	windows_10_20h2	—
Windows	microsoft	windows_10_21h2	—
Windows	microsoft	windows_10_22h2	—
Windows	microsoft	windows_11_21h2	—
Windows	microsoft	windows_11_22h2	—
Windows	microsoft	windows_server_2008	`r2`
Windows	microsoft	windows_server_2008	—
Windows	microsoft	windows_server_2012	`r2`
Windows	microsoft	windows_server_2012	—
Windows	microsoft	windows_server_2016	—
Windows	microsoft	windows_server_2019	—
Windows	microsoft	windows_server_2022	—

Weakness classes (CWE)

CWE-122Heap-based Buffer Overflow
Variant
A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().
Entry at MITRE CWE-122

Public exploit references

Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

Public exploit references

CISA KEV Catalog	CISA Known Exploited Vulnerability (opens in a new tab)cisa.gov	actively exploited	11.04.2023
CSA/SingCERT	Multiple Vulnerabilities in Microsoft Products (opens in a new tab)CSA/SingCERT	actively exploited	13.04.2023
Packet Storm	Windows Common Log File System Driver clfs.sys Privilege Escalation (opens in a new tab)packetstormsecurity.com	PoC (publicly reported)reported, not verified	—

References & sources

Microsoft Security Update GuideWindows Common Log File System Driver Elevation of Privilege VulnerabilityVendor advisory, Patch, Vendor advisory
cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2023-28252government-resource, US government resource
packetstormsecurity.comfiles/174668/Windows-Common-Log-File-System-Driver-clfs.sys-Pri…x_transferred, Exploit, Third-party advisory, Vulnerability database
pwn.watchpwn.watch: Microsoft Windows: Common Log File System (CLFS) Driver Privilege Escalation (CVE-2023-28252)pwn-watch
Microsoft Security Update GuideVendor advisory: Microsoft Windowspwn-watch
NVD (NIST)NVD: CVE-2023-28252pwn-watch
cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch

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<a href="https://intel.neosec.eu/en/cve/CVE-2023-28252"><img src="https://intel.neosec.eu/badge/cve/CVE-2023-28252.svg?lang=en" alt="CVE-2023-28252 – NEOSEC Intel" height="20"></a>

What is affected, what to do

Metrics

Response and mitigation

Prioritisation rationale

Immediate response (0-24 h)

Mitigation layers

Detection rules

Detection rules

Classification under NIS2 and CRA

Description

Affected products

Vendors and products

Affected operating systems

Weakness classes (CWE)

Public exploit references

References & sources