CVE-2020-0849: Windows Hard Link Elevation of Privilege Vulnerability

CVE-2020-0849 is an elevation of privilege vulnerability in Windows Hard Link, rated Important by Microsoft, with a CVSS 3.0 base score of 7.8 (High). An attacker can exploit it by an attacker with local access, with low privileges and without user interaction. Microsoft has not reported exploitation in the wild and rates exploitation as less likely. The EPSS model estimates a 0.88% probability of exploitation activity in the next 30 days, higher than 59% of all scored vulnerabilities. Microsoft released the fix on 10 March 2020 in the March 2020 Patch Tuesday, delivered through 14 security updates (KB4540689, KB4538461, KB4540673, KB4540681 and more). It affects 41 products in 2 product families (Windows, ESU).

Key facts

CVE ID: CVE-2020-0849
Severity: High CVSS 7.8
Microsoft severity: Important
Impact: Elevation of Privilege
Exploited in the wild: No
Publicly disclosed: No
Exploitation likelihood: Less Likely
EPSS: 0.88% (percentile 59%)
CISA KEV: Not listed
Released: 10 March 2020
Last updated: 10 March 2020
Patch Tuesday: March 2020 Patch Tuesday
Product families: Windows, ESU

CVSS score and vector

Microsoft scores CVE-2020-0849 at 7.8 (temporal 7) using CVSS 3.0. Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:P/RL:O/RC:C

Metric	Value
Attack vector	Local
Attack complexity	Low
Privileges required	Low
User interaction	None
Scope	Unchanged
Confidentiality impact	High
Integrity impact	High
Availability impact	High
Exploit code maturity	Proof of concept
Remediation level	Official fix
Report confidence	Confirmed

NVD scores it 7.8 (HIGH) with CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

Description

An elevation of privilege vulnerability exists when Windows improperly handles hard links. An attacker who successfully exploited this vulnerability could overwrite a targeted file leading to an elevated status.

To exploit this vulnerability, an attacker would first have to log on to the system. An attacker could then run a specially crafted application that could exploit the vulnerability and take control of an affected system.

The security update addresses the vulnerability by correcting how Windows handles hard links.

Affected products (41)

Windows

Product	Security update	Type	Restart
Windows 10 Version 1803 for 32-bit Systems	KB4540689	Security Update	Yes
Windows 10 Version 1803 for x64-based Systems	KB4540689	Security Update	Yes
Windows Server, version 1803 (Server Core Installation)	KB4540689	Security Update	Yes
Windows 10 Version 1803 for ARM64-based Systems	KB4540689	Security Update	Yes
Windows 10 Version 1809 for 32-bit Systems	KB4538461	Security Update	Yes
Windows 10 Version 1809 for x64-based Systems	KB4538461	Security Update	Yes
Windows 10 Version 1809 for ARM64-based Systems	KB4538461	Security Update	Yes
Windows Server 2019	KB4538461	Security Update	Yes
Windows Server 2019 (Server Core installation)	KB4538461	Security Update	Yes
Windows 10 Version 1909 for 32-bit Systems	KB4540673	Security Update	Yes
Windows 10 Version 1909 for x64-based Systems	KB4540673	Security Update	Yes
Windows 10 Version 1909 for ARM64-based Systems	KB4540673	Security Update	Yes
Windows Server, version 1909 (Server Core installation)	KB4540673	Security Update	Yes
Windows 10 Version 1709 for 32-bit Systems	KB4540681	Security Update	Yes
Windows 10 Version 1709 for x64-based Systems	KB4540681	Security Update	Yes
Windows 10 Version 1709 for ARM64-based Systems	KB4540681	Security Update	Yes
Windows 10 Version 1903 for 32-bit Systems	KB4540673	Security Update	Yes
Windows 10 Version 1903 for x64-based Systems	KB4540673	Security Update	Yes
Windows 10 Version 1903 for ARM64-based Systems	KB4540673	Security Update	Yes
Windows Server, version 1903 (Server Core installation)	KB4540673	Security Update	Yes
Windows 10 for 32-bit Systems	KB4540693	Security Update	Yes
Windows 10 for x64-based Systems	KB4540693	Security Update	Yes
Windows 10 Version 1607 for 32-bit Systems	KB4540670	Security Update	Yes
Windows 10 Version 1607 for x64-based Systems	KB4540670	Security Update	Yes
Windows Server 2016	KB4540670	Security Update	Yes
Windows Server 2016 (Server Core installation)	KB4540670	Security Update	Yes
Windows 8.1 for 32-bit systems	KB4541509 KB4541505	Monthly Rollup Security Only	Yes Yes
Windows 8.1 for x64-based systems	KB4541509 KB4541505	Monthly Rollup Security Only	Yes Yes
Windows RT 8.1	KB4541509	Monthly Rollup	Yes
Windows Server 2012	KB4541510 KB4540694	Monthly Rollup Security Only	Yes Yes
Windows Server 2012 (Server Core installation)	KB4541510 KB4540694	Monthly Rollup Security Only	Yes Yes
Windows Server 2012 R2	KB4541509 KB4541505	Monthly Rollup Security Only	Yes Yes
Windows Server 2012 R2 (Server Core installation)	KB4541509 KB4541505	Monthly Rollup Security Only	Yes Yes

ESU

Product	Security update	Type	Restart
Windows 7 for 32-bit Systems Service Pack 1	KB4540688 KB4541500	Monthly Rollup Security Only	Yes Yes
Windows 7 for x64-based Systems Service Pack 1	KB4540688 KB4541500	Monthly Rollup Security Only	Yes Yes
Windows Server 2008 for 32-bit Systems Service Pack 2	KB4541506 KB4541504	Monthly Rollup Security Only	Yes Yes
Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation)	KB4541506 KB4541504	Monthly Rollup Security Only	Yes Yes
Windows Server 2008 for x64-based Systems Service Pack 2	KB4541506 KB4541504	Monthly Rollup Security Only	Yes Yes
Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation)	KB4541506 KB4541504	Monthly Rollup Security Only	Yes Yes
Windows Server 2008 R2 for x64-based Systems Service Pack 1	KB4540688 KB4541500	Monthly Rollup Security Only	Yes Yes
Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation)	KB4540688 KB4541500	Monthly Rollup Security Only	Yes Yes

Security updates (14)

KB4540689 (Security Update)
KB4538461 (Security Update)
KB4540673 (Security Update)
KB4540681 (Security Update)
KB4540693 (Security Update)
KB4540670 (Security Update)
KB4540688 (Monthly Rollup)
KB4541500 (Security Only)
KB4541509 (Monthly Rollup)
KB4541505 (Security Only)
KB4541506 (Monthly Rollup)
KB4541504 (Security Only)
KB4541510 (Monthly Rollup)
KB4540694 (Security Only)

NIST NVD data

NVD status: Modified
NVD CVSS: 7.8 (HIGH)
Published to NVD: 12 March 2020
NVD last modified: 17 June 2026

Affected configurations (CPE)

Product	Vulnerable versions
windows 10	all listed versions
windows 10 1607	all listed versions
windows 10 1709	all listed versions
windows 10 1803	all listed versions
windows 10 1809	all listed versions
windows 10 1903	all listed versions
windows 10 1909	all listed versions
windows 7	all listed versions
windows 8.1	all listed versions
windows rt 8.1	all listed versions
windows server 2008	all listed versions
windows server 2008 r2 (itanium)	all listed versions
windows server 2008 r2 (x64)	all listed versions
windows server 2012	all listed versions
windows server 2012 r2	all listed versions
windows server 2016	all listed versions
windows server 2016 1803	all listed versions
windows server 2016 1903	all listed versions
windows server 2016 1909	all listed versions
windows server 2019	all listed versions

References

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-0849 (Patch, Vendor Advisory)
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-0849 (Patch, Vendor Advisory)

Acknowledgments

Georgios Baltas of MSRC Vulnerabilities & Mitigations Team
Zhiniang Peng (@edwardzpeng) of Qihoo 360 Core security & Xuefeng Li
Zhiniang Peng (@edwardzpeng) of Qihoo 360 Core security & Jiadong Lu
Zhiniang Peng (@edwardzpeng) of Qihoo 360 Core security & Xuefeng Li

Revision history

Version	Date	Description
1.0	10 March 2020	Information published.