CVE-2023-21549: Windows SMB Witness Service Elevation of Privilege Vulnerability

CVE-2023-21549 is an elevation of privilege vulnerability in Windows SMB Witness Service, rated Important by Microsoft, with a CVSS 3.1 base score of 8.8 (High). An attacker can exploit it remotely over the network, with low privileges and without user interaction. Microsoft has not reported exploitation in the wild and rates exploitation as less likely. It was publicly disclosed before the fix was released. The EPSS model estimates a 1.39% probability of exploitation activity in the next 30 days, higher than 73% of all scored vulnerabilities. Microsoft released the fix on 10 January 2023 in the January 2023 Patch Tuesday, delivered through 11 security updates (KB5022286, KB5022291, KB5022282, KB5022287 and more). It affects 32 products in 2 product families (Windows, ESU).

Key facts

CVE ID: CVE-2023-21549
Severity: High CVSS 8.8
Microsoft severity: Important
Impact: Elevation of Privilege
Exploited in the wild: No
Publicly disclosed: Yes
Exploitation likelihood: Less Likely
Weakness: CWE-285; CWE-269
EPSS: 1.39% (percentile 73%)
CISA KEV: Not listed
Released: 10 January 2023
Last updated: 23 January 2023
Patch Tuesday: January 2023 Patch Tuesday
Product families: Windows, ESU

CVSS score and vector

Microsoft scores CVE-2023-21549 at 8.8 (temporal 7.7) using CVSS 3.1. Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

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

Frequently asked questions (Microsoft)

How could an attacker exploit the vulnerability?

To exploit this vulnerability, an attacker could execute a specially crafted malicious script which executes an RPC call to an RPC host. This could result in elevation of privilege on the server.

What privileges could be gained by an attacker who successfully exploited the vulnerability?

An attacker who successfully exploited this vulnerability could execute RPC functions that are restricted to privileged accounts only.

Affected products (32)

Windows

Product	Security update	Type	Fixed build	Restart
Windows 10 Version 1809 for 32-bit Systems	KB5022286	Security Update	10.0.17763.3887	Yes
Windows 10 Version 1809 for x64-based Systems	KB5022286	Security Update	10.0.17763.3887	Yes
Windows 10 Version 1809 for ARM64-based Systems	KB5022286	Security Update	10.0.17763.3887	Yes
Windows Server 2019	KB5022286	Security Update	10.0.17763.3887	Yes
Windows Server 2019 (Server Core installation)	KB5022286	Security Update	10.0.17763.3887	Yes
Windows Server 2022	KB5022291	Security Update	10.0.20348.1487	Yes
Windows Server 2022 (Server Core installation)	KB5022291	Security Update	10.0.20348.1487	Yes
Windows 10 Version 20H2 for 32-bit Systems	KB5022282	Security Update	10.0.19042.2486	Yes
Windows 10 Version 20H2 for ARM64-based Systems	KB5022282	Security Update	10.0.19042.2486	Yes
Windows 11 version 21H2 for x64-based Systems	KB5022287	Security Update	10.0.22000.1455	Yes
Windows 11 version 21H2 for ARM64-based Systems	KB5022287	Security Update	10.0.22000.1455	Yes
Windows 10 Version 21H2 for 32-bit Systems
Windows 10 Version 21H2 for ARM64-based Systems
Windows 10 Version 21H2 for x64-based Systems
Windows 11 Version 22H2 for ARM64-based Systems	KB5022303	Security Update	10.0.22621.1105	Yes
Windows 11 Version 22H2 for x64-based Systems	KB5022303	Security Update	10.0.22621.1105	Yes
Windows 10 Version 22H2 for x64-based Systems
Windows 10 Version 22H2 for ARM64-based Systems
Windows 10 Version 22H2 for 32-bit Systems
Windows 10 for 32-bit Systems	KB5022297	Security Update	10.0.10240.19685	Yes
Windows 10 for x64-based Systems	KB5022297	Security Update	10.0.10240.19685	Yes
Windows 10 Version 1607 for 32-bit Systems	KB5022289	Security Update	10.0.14393.5648	Yes
Windows 10 Version 1607 for x64-based Systems	KB5022289	Security Update	10.0.14393.5648	Yes
Windows Server 2016	KB5022289	Security Update	10.0.14393.5648	Yes
Windows Server 2016 (Server Core installation)	KB5022289	Security Update	10.0.14393.5648	Yes
Windows 8.1 for 32-bit systems	KB5022352 KB5022346	Monthly Rollup Security Only	6.3.9600.20778 6.3.9600.20778	Yes Yes
Windows 8.1 for x64-based systems	KB5022352 KB5022346	Monthly Rollup Security Only	6.3.9600.20778 6.3.9600.20778	Yes Yes
Windows RT 8.1	KB5022346	Security Only	6.3.9600.20778	Yes

ESU

Product	Security update	Type	Fixed build	Restart
Windows Server 2012	KB5022348 KB5022343	Monthly Rollup Security Only	6.2.9200.24075 6.2.9200.24075	Yes Yes
Windows Server 2012 (Server Core installation)	KB5022348 KB5022343	Monthly Rollup Security Only	6.2.9200.24075 6.2.9200.24075	Yes Yes
Windows Server 2012 R2	KB5022352 KB5022346	Monthly Rollup Security Only	6.3.9600.20778 6.3.9600.20778	Yes Yes
Windows Server 2012 R2 (Server Core installation)	KB5022352 KB5022346	Monthly Rollup Security Only	6.3.9600.20778 6.3.9600.20778	Yes Yes

Security updates (11)

KB5022286 (Security Update)
KB5022291 (Security Update)
KB5022282 (Security Update)
KB5022287 (Security Update)
KB5022303 (Security Update)
KB5022297 (Security Update)
KB5022289 (Security Update)
KB5022352 (Monthly Rollup)
KB5022346 (Security Only)
KB5022348 (Monthly Rollup)
KB5022343 (Security Only)

NIST NVD data

NVD status: Modified
NVD CVSS: 8.8 (HIGH)
NVD weakness: CWE-285; CWE-269
Published to NVD: 10 January 2023
NVD last modified: 17 June 2026

Affected configurations (CPE)

Product	Vulnerable versions
windows 10 1607 (x64)	all listed versions
windows 10 1607 (x86)	all listed versions
windows 10 1809 (arm64)	all listed versions
windows 10 1809 (x64)	all listed versions
windows 10 1809 (x86)	all listed versions
windows 10 20h2 (arm64)	all listed versions
windows 10 20h2 (x64)	all listed versions
windows 10 20h2 (x86)	all listed versions
windows 10 21h2 (arm64)	all listed versions
windows 10 21h2 (x64)	all listed versions
windows 10 21h2 (x86)	all listed versions
windows 10 22h2 (arm64)	all listed versions
windows 10 22h2 (x64)	all listed versions
windows 10 22h2 (x86)	all listed versions
windows 11 21h2 (arm64)	all listed versions
windows 11 21h2 (x64)	all listed versions
windows 11 22h2 (arm64)	all listed versions
windows 11 22h2 (x64)	all listed versions
windows 7 (x86)	all listed versions
windows 8.1 (x64)	all listed versions
windows rt 8.1	all listed versions
windows server 2012	all listed versions
windows server 2012 r2	all listed versions
windows server 2016	all listed versions
windows server 2019	all listed versions
windows server 2022	all listed versions

References

Acknowledgments

Stiv Kupchik and Ophir Harpaz with Akamai

Revision history

Version	Date	Description
1.0	10 January 2023	Information published.
1.1	17 January 2023	Updated CVE Tag. This is an informational change only.
2.0	23 January 2023	Revised the Security Updates table to include Windows 8.1 for 32-bit systems because it is affected by CVE-2023-21524 and removed Windows 7 for 32-bit Systems Service Pack 1 as it is not affected. Microsoft recommends that customers running Windows 8.1 for 32-bit systems should install security update 5022338 to be protected from this vulnerability.