OnlyPatch
Windows Kernel

CVE-2020-17087 — Windows Kernel Local Elevation of Privilege Vulnerability

Important CVSS 7.8 EPSS 0.05431 ⚠️ Exploited in the wild 📢 Publicly disclosed 🔬 Patch diffed 2020-11 archive

Executive Summary

None

Overview

7.8
CVSS HIGH
Important
MS Severity
Exploited
MS Exploit Status
Exploitation Detected
MS Exploit Likelihood
Category Elevation of Privilege
Released Nov 10 2020
Last Updated Nov 10 2020
Publicly Disclosed Yes
CISA KEV Not Listed
Known Exploits None Known
EPSS Score 0.05431 — 0.92005 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:F/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
Functional
REMEDIATION LEVEL
Official Fix
REPORT CONFIDENCE
Confirmed
Temporal Score: 7.2

EPSS Score

0.05431
probability of exploitation in the next 30 days
0.92005 percentile - updated 2026-08-14
View on FIRST.org

Affected Products

30 affected products
Product KB Article Severity Impact Restart Required
Windows 10 for 32-bit Systems 4586787 (Security Update) Important Elevation of Privilege Yes
Windows 10 for x64-based Systems 4586787 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1607 for 32-bit Systems 4586830 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1607 for x64-based Systems 4586830 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1803 for 32-bit Systems 4586785 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1803 for ARM64-based Systems 4586785 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1803 for x64-based Systems 4586785 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1809 for 32-bit Systems 4586793 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1809 for ARM64-based Systems 4586793 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1809 for x64-based Systems 4586793 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1903 for 32-bit Systems 4586786 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1903 for ARM64-based Systems 4586786 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1903 for x64-based Systems 4586786 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1909 for 32-bit Systems 4586786 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1909 for ARM64-based Systems 4586786 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1909 for x64-based Systems 4586786 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 2004 for 32-bit Systems 4586781 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 2004 for ARM64-based Systems 4586781 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 2004 for x64-based Systems 4586781 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 20H2 for 32-bit Systems 4586781 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 20H2 for ARM64-based Systems 4586781 (Security Update) Important Elevation of Privilege Yes
Windows 7 for 32-bit Systems Service Pack 1 4586827 (Monthly Rollup) 4586805 (Security Only) Important Elevation of Privilege 4580345 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C Yes 4586827 4586805 Windows 7 for x64-based Systems Service Pack 1 4586827 (Monthly Rollup) 4586805 (Security Only) Important Elevation of Privilege 4580345 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C Yes 4586827 4586805 Windows 8.1 for 32-bit systems 4586845 (Monthly Rollup) 4586823 (Security Only) Important Elevation of Privilege 4580347 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C Yes 4586845 4586823 Windows 8.1 for x64-based systems 4586845 (Monthly Rollup) 4586823 (Security Only) Important Elevation of Privilege 4580347 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C Yes 4586845 4586823 Windows RT 8.1 4586845 (Monthly Rollup) Important Elevation of Privilege Yes
Windows Server 2008 for 32-bit Systems Service Pack 2 4586807 (Monthly Rollup) 4586817 (Security Only) Important Elevation of Privilege 4580378 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C Yes 4586807 4586817 Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation) 4586807 (Monthly Rollup) 4586817 (Security Only) Important Elevation of Privilege 4580378 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C Yes 4586807 4586817 Windows Server 2008 for x64-based Systems Service Pack 2 4586807 (Monthly Rollup) 4586817 (Security Only) Important Elevation of Privilege 4580378 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C Yes 4586807 4586817 Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation) 4586807 (Monthly Rollup) 4586817 (Security Only) Important Elevation of Privilege 4580378 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C Yes 4586807 4586817 Windows Server 2008 R2 for x64-based Systems Service Pack 1 4586827 (Monthly Rollup) 4586805 (Security Only) Important Elevation of Privilege 4580345 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C Yes 4586827 4586805 Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation) 4586827 (Monthly Rollup) 4586805 (Security Only) Important Elevation of Privilege 4580345 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C Yes 4586827 4586805 Windows Server 2012 4598278 (Monthly Rollup) 4598297 (Security Only) Important Elevation of Privilege 4592468 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C Yes 4598278 4598297 Windows Server 2012 (Server Core installation) 4598278 (Monthly Rollup) 4598297 (Security Only) Important Elevation of Privilege 4592468 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C Yes 4598278 4598297 Windows Server 2012 R2 4586845 (Monthly Rollup) 4586823 (Security Only) Important Elevation of Privilege 4580347 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C Yes 4586845 4586823 Windows Server 2012 R2 (Server Core installation) 4586845 (Monthly Rollup) 4586823 (Security Only) Important Elevation of Privilege 4580347 Base: 7.8 Temporal: 7.2 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C Yes 4586845 4586823 Windows Server 2016 4586830 (Security Update) Important Elevation of Privilege Yes
Windows Server 2016 (Server Core installation) 4586830 (Security Update) Important Elevation of Privilege Yes
Windows Server 2019 4586793 (Security Update) Important Elevation of Privilege Yes
Windows Server 2019 (Server Core installation) 4586793 (Security Update) Important Elevation of Privilege Yes
Windows Server, version 1903 (Server Core installation) 4586786 (Security Update) Important Elevation of Privilege Yes
Windows Server, version 1909 (Server Core installation) 4586786 (Security Update) Important Elevation of Privilege Yes
Windows Server, version 2004 (Server Core installation) 4586781 (Security Update) Important Elevation of Privilege Yes
Windows Server, version 20H2 (Server Core Installation) 4586781 (Security Update) Important Elevation of Privilege Yes

Patches

7 patches
Article Type Restart
4586787 Security Update Yes
4586830 Security Update Yes
4586785 Security Update Yes
4586793 Security Update Yes
4586786 Security Update Yes
4586781 Security Update Yes
4586845 Monthly Rollup Yes

Patch Diff

ghidriff + headless Ghidra decompile verification · cng.sys (KB4586781)

Pool buffer overflow (CWE-190 integer truncation) in cng.sys IOCTL 0x390400 handling: cng!CfgAdtpFormatPropertyBlock computes the output allocation as SrcLen*6 in 16-bit arithmetic but writes SrcLen*6 bytes of Unicode hex dump, giving a controlled-length linear NonPagedPoolNx overflow with a XX 00 XX 00 20 00 byte pattern. Reachable by any local user via DeviceIoControl on \\.\GLOBALROOT\Device\Cng (or BCryptSetContextFunctionProperty). Exploited ITW as the sandbox-escape stage of a Chrome chain (with CVE-2020-15999); full public technique via Segment Heap BlockSize attack + named-pipe DQE abuse + quota ProcessBilled decrement -> SeDebugPrivilege (PixiePoint). Patch (KB4586781, cng.sys 10.0.19041.630) replaces the inline multiply with new helper RtlUShortMult and rejects on overflow; VERIFIED 2026-07-22 via ghidriff + headless decompile (single code-changed function).

Pre-patch version 10.0.19041.264 Download
Post-patch version 10.0.19041.630 Download
Function Address Change Note
cng!CfgAdtpFormatPropertyBlock 0x1c006245c (both builds) code (verified via headless decompile 2026-07-22) 16-bit truncation: BCryptAlloc((USHORT)(SrcLen*6)) while the hex-format loop writes SrcLen*6 bytes -> NonPagedPoolNx linear overflow ('Cngb' tag), content pattern XX 00 XX 00 20 00. SrcLen>=0x2AAB triggers ((ushort)(0x2AAB*6)=2 allocated, 0x10002 written). Length also truncated to 16-bit at the CfgAdtReportFunctionPropertyOperation call site. Fix: RtlUShortMult(len,6,&out) with error-on-overflow before allocation + BCryptFree cleanup path.
cng!RtlUShortMult added Safe 16-bit multiply returning error on overflow; the entire fix
cng!BCryptFree modified (no code changes) metadata-only churn
View full diff report View RCA report Download PoC

Attack Path

Sandbox escape to SYSTEM via a 16-bit truncation in the cng.sys IOCTL property dump - the Windows half of a Chrome exploit chain

Attack path for CVE-2020-17087 Sandbox escape to SYSTEM via a 16-bit truncation in the cng.sys IOCTL property dump - the Windows half of a Chrome exploit chain 01 — ENTRY Any local user, including code inside a browser sandbox, opens the CNG device DeviceIoControl on \\.\GLOBALROOT\Device\Cng, IOCTL 0x390400, or the same path via BCryptSetContextFunctionProperty. No privileges required - this is what made it usable as a Chrome sandbox escape. 02 — CONTROLLED INPUT Attacker chooses SrcLen so that SrcLen * 6 exceeds 16 bits The source length is fully caller-controlled through the IOCTL input buffer. 03 — PATH The IOCTL handler formats the property block as a Unicode hex dump cng!CfgAdtpFormatPropertyBlock computes the output allocation and then writes the dump into it. 04 — MISSING CHECK The allocation size is computed as SrcLen * 6 in 16-bit arithmetic, the write is not The multiply truncates to 16 bits for the allocation, but the formatting loop writes the full SrcLen * 6 bytes. CWE-190 integer truncation. The patch widens the size computation. 05 — PRIMITIVE Controlled-length linear NonPagedPoolNx overflow with a fixed byte pattern Overflow bytes follow the XX 00 XX 00 20 00 hex-dump pattern. Public technique pairs a Segment Heap BlockSize attack with named-pipe data queue entries. Chained with CVE-2020-15999 in the wild.

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

Microsoft would like to thank Qualys for co-ordinated vulnerability disclosure on identifying a regression for the Windows Server 2012 version of this security update.
Mateusz Jurczyk and Sergei Glazunov of Google Project Zero

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