CVE-2025-55336 — Windows Cloud Files Mini Filter Driver Information Disclosure Vulnerability
Executive Summary
Exposure of sensitive information to an unauthorized actor in Windows Cloud Files Mini Filter Driver allows an authorized attacker to disclose information locally.
Overview
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
EPSS Score
Affected Products
| Product | KB Article | Severity | Impact | Restart Required |
|---|---|---|---|---|
| Windows 10 Version 1809 for 32-bit Systems | 5066586 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 10 Version 1809 for x64-based Systems | 5066586 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 10 Version 21H2 for 32-bit Systems | 5066791 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 10 Version 21H2 for ARM64-based Systems | 5066791 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 10 Version 21H2 for x64-based Systems | 5066791 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 10 Version 22H2 for 32-bit Systems | 5066791 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 10 Version 22H2 for ARM64-based Systems | 5066791 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 10 Version 22H2 for x64-based Systems | 5066791 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 11 Version 22H2 for ARM64-based Systems | 5066793 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 11 Version 22H2 for x64-based Systems | 5066793 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 11 Version 23H2 for ARM64-based Systems | 5066793 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 11 Version 23H2 for x64-based Systems | 5066793 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 11 Version 24H2 for ARM64-based Systems | 5066835 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 11 Version 24H2 for x64-based Systems | 5066835 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 11 Version 25H2 for ARM64-based Systems | 5066835 (Security Update) |
Important | Information Disclosure | Yes |
| Windows 11 Version 25H2 for x64-based Systems | 5066835 (Security Update) |
Important | Information Disclosure | Yes |
| Windows Server 2019 | 5066586 (Security Update) |
Important | Information Disclosure | Yes |
| Windows Server 2019 (Server Core installation) | 5066586 (Security Update) |
Important | Information Disclosure | Yes |
| Windows Server 2022 | 5066782 (Security Update) |
Important | Information Disclosure | Yes |
| Windows Server 2022 (Server Core installation) | 5066782 (Security Update) |
Important | Information Disclosure | Yes |
| Windows Server 2022, 23H2 Edition (Server Core installation) | 5066780 (Security Update) |
Important | Information Disclosure | Yes |
| Windows Server 2025 | 5066835 (Security Update) |
Important | Information Disclosure | Yes |
| Windows Server 2025 (Server Core installation) | 5066835 (Security Update) |
Important | Information Disclosure | Yes |
Patches
| Article | Type | Restart |
|---|---|---|
5066586 |
Security Update | Yes |
5066791 |
Security Update | Yes |
5066793 |
Security Update | Yes |
5066835 |
Security Update | Yes |
5066782 |
Security Update | Yes |
5066780 |
Security Update | Yes |
Patch Diff
Information disclosure (CWE-200) in the Windows Cloud Files Mini Filter Driver cldflt.sys, local kernel memory-address leak (Important, AV:L, C:H/I:N/A:N, CVSS 5.5). CldStreamQueryProgress services a user query for cloud-file stream operation progress and copies an array of fixed-size progress records into a user-supplied output buffer (after ProbeForWrite). PRE: the progress records were populated without fully initializing every field, so residual kernel stack/pool contents - including a kernel memory address - were left in the output and exposed to the caller; per the MSRC FAQ the disclosed data is a memory address within kernel space (defeats KASLR). Diff of cldflt.sys 10.0.22621.5766 (KB5065431, Sept) -> .6060 (KB5066793, Oct 14 2025; 23H2, OS build 22631.6060) confirms the fix: gated behind CFR flag Feature_899985722, CldStreamQueryProgress (length 5255 -> 5527 bytes) adds zero-initialization/sanitization of the record buffer before the copy-to-user, so no uninitialized kernel memory (or kernel address) remains in the fields written to the caller. Stated at confirmed-changed level (the October update also reworks placeholder handling under Feature_29931835; the isolable info-disclosure mechanism is the CldStreamQueryProgress output initialization). Sourcing note: the msdl coords B5371DB0/F5F18A33 are ambiguous (TimeDateStamp+size collide with other cldflt builds .5983/.1488); the authoritative pair by winbindex SHA is .5766 -> .6060.
| Function | Address | Change | Note |
|---|---|---|---|
CldStreamQueryProgress |
code change |
code (output progress records now zero-initialized before copyout, CFR-gated) | Pre: progress records copied to the user output buffer (param_2, via ProbeForWrite) without fully initializing every field, exposing uninitialized kernel memory including a kernel address. Post (Feature_899985722): function grew 5255 -> 5527 bytes and zero-initializes/sanitizes the record buffer before copyout. |
HsmpOpCreatePlaceholders / CldiPortProcessAbortHydration |
code change |
code (placeholder/hydration handling reworked in same update) | HsmpOpCreatePlaceholders switched from direct MDL mapping of the user buffer to a zero-initialized kernel bounce buffer (ExAllocatePool2) with ProbeForRead/ProbeForWrite (Feature_29931835); CldiPortProcessAbortHydration field handling adjusted. Not the primary info-disclosure site. |
Feature_899985722 |
gate |
added (CFR gate) | CFR flag gating the CldStreamQueryProgress output-record initialization; the original path still ships when disabled. |
Attack Path
A cloud-files progress query returns uninitialized kernel memory, leaking a kernel address
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.