OnlyPatch
Microsoft Streaming Service

CVE-2025-59514 — Microsoft Streaming Service Proxy Elevation of Privilege Vulnerability

Important CVSS 7.8 EPSS 0.00359 🔬 Patch diffed 2025-11 archive

Executive Summary

Improper privilege management in Microsoft Streaming Service allows an authorized attacker to elevate privileges locally.

Overview

7.8
CVSS HIGH
Important
MS Severity
Not Exploited
MS Exploit Status
Exploitation Unlikely
MS Exploit Likelihood
Category Elevation of Privilege
Weakness CWE-269: Improper Privilege Management
Released Nov 11 2025
Last Updated Nov 11 2025
Publicly Disclosed No
CISA KEV Not Listed
Known Exploits None Known
EPSS Score 0.00359 — 0.28869 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

0.00359
probability of exploitation in the next 30 days
0.28869 percentile - updated 2026-08-14
View on FIRST.org

Affected Products

21 affected products
Product KB Article Severity Impact Restart Required
Windows 10 Version 1607 for 32-bit Systems 5068864 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1607 for x64-based Systems 5068864 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1809 for 32-bit Systems 5068791 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1809 for x64-based Systems 5068791 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 21H2 for 32-bit Systems 5068781 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 21H2 for ARM64-based Systems 5068781 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 21H2 for x64-based Systems 5068781 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 22H2 for 32-bit Systems 5068781 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 22H2 for ARM64-based Systems 5068781 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 22H2 for x64-based Systems 5068781 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 23H2 for ARM64-based Systems 5068865 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 23H2 for x64-based Systems 5068865 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 24H2 for ARM64-based Systems 5068861 (Security Update) 5068966 (Security Hotpatch Update) Important Elevation of Privilege 5066835 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 10.0.26100.7171 10.0.26100.7092 Yes None Windows 11 Version 24H2 for x64-based Systems 5068861 (Security Update) 5068966 (Security Hotpatch Update) Important Elevation of Privilege 5066835 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 10.0.26100.7171 10.0.26100.7092 Yes None Windows 11 Version 25H2 for ARM64-based Systems 5068861 (Security Update) 5068966 (Security Hotpatch Update) Important Elevation of Privilege 5066835 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 10.0.26200.7171 10.0.26200.7092 Yes None Windows 11 Version 25H2 for x64-based Systems 5068861 (Security Update) 5068966 (Security Hotpatch Update) Important Elevation of Privilege 5066835 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 10.0.26200.7171 10.0.26200.7092 Yes None Windows Server 2008 for 32-bit Systems Service Pack 2 5068906 (Monthly Rollup) 5068909 (Security Only) Important Elevation of Privilege 5066874 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 6.0.6003.23624 Yes None Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation) 5068906 (Monthly Rollup) 5068909 (Security Only) Important Elevation of Privilege 5066874 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 6.0.6003.23624 Yes None Windows Server 2008 for x64-based Systems Service Pack 2 5068906 (Monthly Rollup) 5068909 (Security Only) Important Elevation of Privilege 5066874 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 6.0.6003.23624 Yes None Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation) 5068906 (Monthly Rollup) 5068909 (Security Only) Important Elevation of Privilege 5066874 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 6.0.6003.23624 Yes None Windows Server 2008 R2 for x64-based Systems Service Pack 1 5068904 (Monthly Rollup) 5068908 (Security Only) Important Elevation of Privilege 5066872 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 6.1.7601.28021 Yes None Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation) 5068904 (Monthly Rollup) 5068908 (Security Only) Important Elevation of Privilege 5066872 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 6.1.7601.28021 Yes None Windows Server 2012 5068907 (Monthly Rollup) Important Elevation of Privilege Yes
Windows Server 2012 (Server Core installation) 5068907 (Monthly Rollup) Important Elevation of Privilege Yes
Windows Server 2012 R2 5068905 (Monthly Rollup) Important Elevation of Privilege Yes
Windows Server 2012 R2 (Server Core installation) 5068905 (Monthly Rollup) Important Elevation of Privilege Yes
Windows Server 2016 5068864 (Security Update) Important Elevation of Privilege Yes
Windows Server 2016 (Server Core installation) 5068864 (Security Update) Important Elevation of Privilege Yes
Windows Server 2019 5068791 (Security Update) Important Elevation of Privilege Yes
Windows Server 2019 (Server Core installation) 5068791 (Security Update) Important Elevation of Privilege Yes
Windows Server 2022 5068787 (Security Update) 5068840 (Security Hotpatch Update) Important Elevation of Privilege 5066782 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 10.0.20348.4405 10.0.20348.4346 Yes None Windows Server 2022 (Server Core installation) 5068787 (Security Update) 5068840 (Security Hotpatch Update) Important Elevation of Privilege 5066782 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 10.0.20348.4405 10.0.20348.4346 Yes None Windows Server 2022, 23H2 Edition (Server Core installation) 5068779 (Security Update) Important Elevation of Privilege Yes

Patches

7 patches
Article Type Restart
5068864 Security Update Yes
5068791 Security Update Yes
5068781 Security Update Yes
5068865 Security Update Yes
5068907 Monthly Rollup Yes
5068905 Monthly Rollup Yes
5068779 Security Update Yes

Patch Diff

ghidriff · mskssrv.sys (KB5068861)

Registry-symlink local EoP (CWE-269/CWE-285) in the Microsoft Kernel Streaming service driver mskssrv.sys ('Microsoft Streaming Service Proxy'). A KSPROPERTY_SERVICE_BUILDCACHE request invokes PropertySrv -> UpdateMediumCache, which walks a device's pins and, for non-standard Medium types, caches data under HKLM\SYSTEM\CurrentControlSet\Control\MediumCache. It creates those keys with ZwCreateKey WITHOUT OBJ_FORCE_ACCESS_CHECK, so the create runs with the driver's SYSTEM authority and does not check the caller. A standard user (who has create-subkey rights under MediumCache) creates a subkey they own, plants a registry symbolic link, and the SYSTEM driver follows it to create/modify the default value of an arbitrary HKLM key -> EoP. Requires a device with custom Medium pins (excluding KSMEDIUMSETID_Standard). IN-HOUSE ghidriff of mskssrv.sys 10.0.26100.7019 -> .7171 (Nov 11 2025) confirms the fix: UpdateMediumCachePassive / UpdateMediumCachePassive_Do (the Medium-cache registry path) are reworked, gated behind CFR flag Feature_3602159931 (expected change: add OBJ_FORCE_ACCESS_CHECK to the ZwCreateKey object attributes). Credit: t0zhang.

Pre-patch version 10.0.26100.7019 Download
Post-patch version 10.0.26100.7171 Download
Function Address Change Note
UpdateMediumCachePassive_Do code change code (access-check on registry create, CFR-gated) Worker that creates the Medium-cache HKLM keys. Pre: ZwCreateKey without OBJ_FORCE_ACCESS_CHECK, so a user-planted registry symlink under MediumCache is followed with SYSTEM authority. Post (Feature_3602159931 enabled): access-checked / non-symlink-followable create.
UpdateMediumCachePassive code change code (caller of the fixed worker) Reworked alongside UpdateMediumCachePassive_Do under the same flag.
Feature_3602159931 new flag added (CFR gate) New Controlled Feature Rollout flag introduced by this patch, gating the MediumCache access-check fix. Both branches ship in .7171.
View full diff report View RCA report

Attack Path

A KS Medium-cache registry create without OBJ_FORCE_ACCESS_CHECK follows a user symlink to write arbitrary HKLM keys as SYSTEM

Attack path for CVE-2025-59514 A KS Medium-cache registry create without OBJ_FORCE_ACCESS_CHECK follows a user symlink to write arbitrary HKLM keys as SYSTEM 01 — ENTRY Low-privileged user sends a KS KSPROPERTY_SERVICE_BUILDCACHE request mskssrv.sys (kernel, SYSTEM) services KS property requests reachable by ordinary users. BUILDCACHE reaches PropertySrv -> UpdateMediumCache. 02 — CONTROLLED INPUT Uses a device with custom (non-standard) Medium pins so the cache path runs For Medium types other than KSMEDIUMSETID_Standard, UpdateMediumCache caches under HKLM\SYSTEM\CurrentControlSet\Control\MediumCache. 03 — PATH The driver creates a subkey under MediumCache with ZwCreateKey MediumCache grants standard users create-subkey rights; the user owns the subkey they create and can set its DACL and plant a registry symbolic link. 04 — MISSING CHECK ZwCreateKey is called without OBJ_FORCE_ACCESS_CHECK The create runs with the driver's SYSTEM authority and does not evaluate the caller or refuse the user-planted symlink (CWE-269/CWE-285). 05 — PRIMITIVE SYSTEM follows the symlink -> arbitrary HKLM key/value create -> EoP The symlink redirects the SYSTEM create to a protected HKLM location, giving an attacker-directed registry write and elevation. The Nov 2025 fix access-checks the create - gated behind CFR flag Feature_3602159931.

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

T0

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