OnlyPatch
Windows Common Log File System Driver

CVE-2021-43224 — Windows Common Log File System Driver Information Disclosure Vulnerability

Important CVSS 5.5 EPSS 0.03872 🔬 Patch diffed 2021-12 archive

Executive Summary

None

Overview

5.5
CVSS MEDIUM
Important
MS Severity
Not Exploited
MS Exploit Status
Less Likely
MS Exploit Likelihood
Category Information Disclosure
Released Dec 14 2021
Last Updated Dec 14 2021
Publicly Disclosed No
CISA KEV Not Listed
Known Exploits None Known
EPSS Score 0.03872 — 0.89269 percentile
NVD CVSS 5.5 MEDIUM — matches MSRC

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C
ATTACK VECTOR
Local
ATTACK COMPLEXITY
Low
PRIVILEGES REQUIRED
Low
USER INTERACTION
None
SCOPE
Unchanged
CONFIDENTIALITY
High
INTEGRITY
None
AVAILABILITY
None
EXPLOIT CODE MATURITY
Unproven
REMEDIATION LEVEL
Official Fix
REPORT CONFIDENCE
Confirmed
Temporal Score: 4.8

EPSS Score

0.03872
probability of exploitation in the next 30 days
0.89269 percentile - updated 2026-08-14
View on FIRST.org

Affected Products

32 affected products
Product KB Article Severity Impact Restart Required
Windows 10 for 32-bit Systems 5008230 (Security Update) Important Information Disclosure Yes
Windows 10 for x64-based Systems 5008230 (Security Update) Important Information Disclosure Yes
Windows 10 Version 1607 for 32-bit Systems 5008207 (Security Update) Important Information Disclosure Yes
Windows 10 Version 1607 for x64-based Systems 5008207 (Security Update) Important Information Disclosure Yes
Windows 10 Version 1809 for 32-bit Systems 5008218 (Security Update) Important Information Disclosure Yes
Windows 10 Version 1809 for ARM64-based Systems 5008218 (Security Update) Important Information Disclosure Yes
Windows 10 Version 1809 for x64-based Systems 5008218 (Security Update) Important Information Disclosure Yes
Windows 10 Version 1909 for 32-bit Systems 5008206 (Security Update) Important Information Disclosure Yes
Windows 10 Version 1909 for ARM64-based Systems 5008206 (Security Update) Important Information Disclosure Yes
Windows 10 Version 1909 for x64-based Systems 5008206 (Security Update) Important Information Disclosure Yes
Windows 10 Version 2004 for 32-bit Systems 5008212 (Security Update) Important Information Disclosure Yes
Windows 10 Version 2004 for ARM64-based Systems 5008212 (Security Update) Important Information Disclosure Yes
Windows 10 Version 2004 for x64-based Systems 5008212 (Security Update) Important Information Disclosure Yes
Windows 10 Version 20H2 for 32-bit Systems 5008212 (Security Update) Important Information Disclosure Yes
Windows 10 Version 20H2 for ARM64-based Systems 5008212 (Security Update) Important Information Disclosure Yes
Windows 10 Version 21H1 for 32-bit Systems 5008212 (Security Update) Important Information Disclosure Yes
Windows 10 Version 21H1 for ARM64-based Systems 5008212 (Security Update) Important Information Disclosure Yes
Windows 10 Version 21H1 for x64-based Systems 5008212 (Security Update) Important Information Disclosure Yes
Windows 10 Version 21H2 for 32-bit Systems 5008212 (Security Update) Important Information Disclosure Yes
Windows 10 Version 21H2 for ARM64-based Systems 5008212 (Security Update) Important Information Disclosure Yes
Windows 10 Version 21H2 for x64-based Systems 5008212 (Security Update) Important Information Disclosure Yes
Windows 11 version 21H2 for ARM64-based Systems 5008215 (Security Update) Important Information Disclosure Yes
Windows 11 version 21H2 for x64-based Systems 5008215 (Security Update) Important Information Disclosure Yes
Windows 7 for 32-bit Systems Service Pack 1 5008244 (Monthly Rollup) 5008282 (Security Only) Important Information Disclosure 5007236 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.1.7601.25796 Yes 5008244 5008282 Windows 7 for x64-based Systems Service Pack 1 5008244 (Monthly Rollup) 5008282 (Security Only) Important Information Disclosure 5007236 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.1.7601.25796 Yes 5008244 5008282 Windows 8.1 for 32-bit systems 5008263 (Monthly Rollup) 5008285 (Security Only) Important Information Disclosure 5007247 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.3.9600.20207 Yes 5008263 5008285 Windows 8.1 for x64-based systems 5008263 (Monthly Rollup) 5008285 (Security Only) Important Information Disclosure 5007247 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.3.9600.20207 Yes 5008263 5008285 Windows RT 8.1 5008263 (Monthly Rollup) Important Information Disclosure Yes
Windows Server 2008 for 32-bit Systems Service Pack 2 5008274 (Monthly Rollup) 5008271 (Security Only) Important Information Disclosure 5007263 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.0.6003.21309 Yes 5008274 5008271 Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation) 5008274 (Monthly Rollup) 5008271 (Security Only) Important Information Disclosure 5007263 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.0.6003.21309 Yes 5008274 5008271 Windows Server 2008 for x64-based Systems Service Pack 2 5008274 (Monthly Rollup) 5008271 (Security Only) Important Information Disclosure 5007263 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.0.6003.21309 Yes 5008274 5008271 Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation) 5008274 (Monthly Rollup) 5008271 (Security Only) Important Information Disclosure 5007263 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.0.6003.21309 Yes 5008274 5008271 Windows Server 2008 R2 for x64-based Systems Service Pack 1 5008244 (Monthly Rollup) 5008282 (Security Only) Important Information Disclosure 5007236 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.1.7601.25796 Yes 5008244 5008282 Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation) 5008244 (Monthly Rollup) 5008282 (Security Only) Important Information Disclosure 5007236 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.1.7601.25796 Yes 5008244 5008282 Windows Server 2012 5008277 (Monthly Rollup) 5008255 (Security Only) Important Information Disclosure 5007260 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.2.9200.23545 6.2.9200.23540 Yes 5008277 5008255 Windows Server 2012 (Server Core installation) 5008277 (Monthly Rollup) 5008255 (Security Only) Important Information Disclosure 5007260 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.2.9200.23545 6.2.9200.23540 Yes 5008277 5008255 Windows Server 2012 R2 5008263 (Monthly Rollup) 5008285 (Security Only) Important Information Disclosure 5007247 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.3.9600.20207 Yes 5008263 5008285 Windows Server 2012 R2 (Server Core installation) 5008263 (Monthly Rollup) 5008285 (Security Only) Important Information Disclosure 5007247 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.3.9600.20207 Yes 5008263 5008285 Windows Server 2016 5008207 (Security Update) Important Information Disclosure Yes
Windows Server 2016 (Server Core installation) 5008207 (Security Update) Important Information Disclosure Yes
Windows Server 2019 5008218 (Security Update) Important Information Disclosure Yes
Windows Server 2019 (Server Core installation) 5008218 (Security Update) Important Information Disclosure Yes
Windows Server 2022 5008223 (Security Update) Important Information Disclosure Yes
Windows Server 2022 (Server Core installation) 5008223 (Security Update) Important Information Disclosure Yes
Windows Server, version 2004 (Server Core installation) 5008212 (Security Update) Important Information Disclosure Yes
Windows Server, version 20H2 (Server Core Installation) 5008212 (Security Update) Important Information Disclosure Yes

Patches

8 patches
Article Type Restart
5008230 Security Update Yes
5008207 Security Update Yes
5008218 Security Update Yes
5008206 Security Update Yes
5008212 Security Update Yes
5008215 Security Update Yes
5008263 Monthly Rollup Yes
5008223 Security Update Yes

Patch Diff

ghidriff · clfs.sys (KB5008212)

Stack buffer overwrite in CClfsLogFcbPhysical::QueryLogFileInfo. User-supplied infoSize passed unclamped to memset() on a 0x78-byte stack buffer — any size >0x78 zeroes past the buffer, corrupting the stack cookie and return address → BSOD. Patch clamps input to sizeof(CLFS_INFORMATION). Reachable via GetLogFileInformation() from any local user.

Pre-patch version 10.0.22000.258 Download
Post-patch version 10.0.22000.376 Download
Function Address Change Note
CClfsLogFcbPhysical::QueryLogFileInfo code (size clamp added) memset size clamped to sizeof(CLFS_INFORMATION) (0x78) before zeroing the stack buffer — prevents overwrite past the 0x78-byte CLFS_INFORMATION structure.
View full diff report View RCA report Download PoC

Attack Path

Stack buffer overwrite via an unclamped memset size in QueryLogFileInfo

Attack path for CVE-2021-43224 Stack buffer overwrite via an unclamped memset size in QueryLogFileInfo 01 — ENTRY Any local user calls GetLogFileInformation() on a log handle CLFS is always present and log handles are obtainable without elevation. 02 — CONTROLLED INPUT The caller supplies infoSize, which is passed straight through No clamping is applied between the user-mode call and the kernel memset. 03 — PATH CClfsLogFcbPhysical::QueryLogFileInfo zeroes a stack buffer The destination is a 0x78-byte CLFS_INFORMATION structure on the kernel stack. 04 — MISSING CHECK memset length is the user-supplied size, not sizeof(CLFS_INFORMATION) Any infoSize greater than 0x78 zeroes past the buffer. The patch clamps the length to sizeof(CLFS_INFORMATION) before the memset. 05 — PRIMITIVE Kernel stack overwrite with zeroes - cookie and return address destroyed Zero-fill rather than controlled content, so the reliable outcome is a bugcheck; corrupting the stack cookie and return address is what makes it more than a hang.

Derived from the patch delta: the checks added by the vendor identify which fields crossed a trust boundary unvalidated. Reachability and privilege are taken from the call chain in the RCA report.

Known Exploits

Acknowledgments

Anonymous
HyungSeok Han

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