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Windows Cloud Files Mini Filter Driver

CVE-2025-50170 — Windows Cloud Files Mini Filter Driver Elevation of Privilege Vulnerability

Important CVSS 7.8 EPSS 0.00396 🔬 Patch diffed 2025-08 archive

Executive Summary

Improper handling of insufficient permissions or privileges in Windows Cloud Files Mini Filter Driver allows an authorized attacker to elevate privileges locally.

Overview

7.8
CVSS HIGH
Important
MS Severity
Not Exploited
MS Exploit Status
Less Likely
MS Exploit Likelihood
Category Elevation of Privilege
Weakness CWE-280: Improper Handling of Insufficient Permissions or Privileges
Released Aug 12 2025
Last Updated Aug 12 2025
Publicly Disclosed No
CISA KEV Not Listed
Known Exploits None Known
EPSS Score 0.00396 — 0.327 percentile
NVD CVSS 7.8 HIGH — matches MSRC

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
ATTACK VECTOR
Local
ATTACK COMPLEXITY
Low
PRIVILEGES REQUIRED
Low
USER INTERACTION
None
SCOPE
Unchanged
CONFIDENTIALITY
High
INTEGRITY
High
AVAILABILITY
High
EXPLOIT CODE MATURITY
Unproven
REMEDIATION LEVEL
Official Fix
REPORT CONFIDENCE
Confirmed
Temporal Score: 6.8

EPSS Score

0.00396
probability of exploitation in the next 30 days
0.327 percentile - updated 2026-08-14
View on FIRST.org

Affected Products

15 affected products
Product KB Article Severity Impact Restart Required
Windows 10 Version 1809 for 32-bit Systems 5063877 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1809 for x64-based Systems 5063877 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 21H2 for 32-bit Systems 5063709 (SecurityUpdate) Important Elevation of Privilege Yes
Windows 10 Version 21H2 for ARM64-based Systems 5063709 (SecurityUpdate) Important Elevation of Privilege Yes
Windows 10 Version 21H2 for x64-based Systems 5063709 (SecurityUpdate) Important Elevation of Privilege Yes
Windows 10 Version 22H2 for 32-bit Systems 5063709 (SecurityUpdate) Important Elevation of Privilege Yes
Windows 10 Version 22H2 for ARM64-based Systems 5063709 (SecurityUpdate) Important Elevation of Privilege Yes
Windows 10 Version 22H2 for x64-based Systems 5063709 (SecurityUpdate) Important Elevation of Privilege Yes
Windows 11 Version 22H2 for ARM64-based Systems 5063875 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 22H2 for x64-based Systems 5063875 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 23H2 for ARM64-based Systems 5063875 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 23H2 for x64-based Systems 5063875 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 24H2 for ARM64-based Systems 5063878 (Security Update) 5064010 (SecurityHotpatchUpdate) Important Elevation of Privilege 5062553 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.26100.4946 10.0.26100.4851 Yes None Windows 11 Version 24H2 for x64-based Systems 5063878 (Security Update) 5064010 (SecurityHotpatchUpdate) Important Elevation of Privilege 5062553 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.26100.4946 10.0.26100.4851 Yes None Windows Server 2019 5063877 (Security Update) Important Elevation of Privilege Yes
Windows Server 2019 (Server Core installation) 5063877 (Security Update) Important Elevation of Privilege Yes
Windows Server 2022 5063880 (SecurityUpdate) 5063812 (SecurityHotpatchUpdate) Important Elevation of Privilege 5062572 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.20348.4052 10.0.20348.3989 Yes None Windows Server 2022 (Server Core installation) 5063880 (SecurityUpdate) 5063812 (SecurityHotpatchUpdate) Important Elevation of Privilege 5062572 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.20348.4052 10.0.20348.3989 Yes None Windows Server 2022, 23H2 Edition (Server Core installation) 5063899 (SecurityUpdate) Important Elevation of Privilege Yes

Patches

4 patches
Article Type Restart
5063877 Security Update Yes
5063709 SecurityUpdate Yes
5063875 Security Update Yes
5063899 SecurityUpdate Yes

Patch Diff

ghidriff · cldflt.sys (KB5063878)

Arbitrary file corruption via IoReadAccess/write mismatch in HsmpOpCreatePlaceholders. Usermode buffer probed with IoReadAccess but written to by kernel, allowing attacker to map read-only victim file and have kernel overwrite it. Fix changes MmProbeAndLockPages to IoWriteAccess via Feature_2594491707.

Pre-patch version 10.0.26100.4484 Download
Post-patch version 10.0.26100.4946 Download
Function Address Change Note
HsmpOpCreatePlaceholders code, length, sig, called MmProbeAndLockPages access mode changed from IoReadAccess to IoWriteAccess via Feature_2594491707
View full diff report View RCA report Download PoC

Attack Path

Kernel writes into a read-only user mapping because the placeholder buffer is locked for read but written back

Attack path for CVE-2025-50170 Kernel writes into a read-only user mapping because the placeholder buffer is locked for read but written back 01 — ENTRY Attacker calls the Cloud Files placeholder-creation API CfCreatePlaceholders() / DeviceIoControl(FSCTL_HSM_CONTROL). cldflt.sys loads by default wherever OneDrive or any Cloud Files consumer runs. Standard user. 02 — CONTROLLED INPUT Supplies a buffer backed by a read-only section mapping of a target file The attacker maps the file they want corrupted read-only - which most system files permit - and hands that address in as the placeholder descriptor buffer. 03 — PATH The FSCTL dispatch locks and maps the buffer into kernel space HsmFltPreFILE_SYSTEM_CONTROL -> HsmFltProcessHSMControl -> HsmFltProcessCreatePlaceholders -> HsmpOpCreatePlaceholders -> IoAllocateMdl -> ProbeForRead -> MmProbeAndLockPages -> MmMapLockedPagesSpecifyCache. 04 — MISSING CHECK Probed and locked for read access, then written to ProbeForRead and MmProbeAndLockPages(UserMode, IoReadAccess=0) establish read-only intent, but the descriptor loop writes per-entry status back through the kernel mapping. Copy-on-write never applies to the kernel VA, so the write lands in the underlying file's pages. 05 — PRIMITIVE Attacker-directed corruption of a file they only have read access to The written bytes are placeholder metadata - timestamps, USN, flags - not fully controlled. Enough to corrupt a DLL or config file, which is a code-execution path in the right target.

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

Chen Le Qi (@cplearns2h4ck)

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