CriticalCVE-2023-21674

Windows Advanced Local Procedure Call (ALPC) Elevation of Privilege Vulnerability (CVE-2023-21674)

Published 10.01.2023In CISA KEV since 10.01.2023Sources: pwn.watch, CVE.org

Actively exploited

What is affected, what to do

Windows Advanced Local Procedure Call (ALPC) Elevation of Privilege Vulnerability

The vulnerability is being actively exploited; treat it as a priority. Update Microsoft Windows 10 Version 1809 to version 10.0.17763.3887, Microsoft Windows Server 2019 to version 10.0.17763.3887, Microsoft Windows Server 2019 (Server Core installation) to version 10.0.17763.3887. Immediate actions, mitigation and detection rules are in the runbook below.

Affected: Microsoft Windows 10 Version 1809 lt 10.0.17763.0..10.0.17763.3887
Microsoft Windows Server 2019 lt 10.0.17763.0..10.0.17763.3887
Microsoft Windows Server 2019 (Server Core installation) lt 10.0.17763.0..10.0.17763.3887
Microsoft Windows Server 2022 lt 10.0.20348.0..10.0.20348.1487
Microsoft Windows 10 Version 20H2 lt 10.0.0..10.0.19042.2486
Microsoft Windows 11 version 21H2 lt 10.0.0..10.0.22000.1455
Microsoft Windows 10 Version 21H2 lt 10.0.19043.0..10.0.19044.2486
Microsoft Windows 11 version 22H2 lt 10.0.22621.0..10.0.22621.1105
Microsoft Windows 10 Version 22H2 lt 10.0.19045.0..10.0.19045.2486
Microsoft Windows 10 Version 1507 lt 10.0.10240.0..10.0.10240.19685
Microsoft Windows 10 Version 1607 lt 10.0.14393.0..10.0.14393.5648
Microsoft Windows Server 2016 lt 10.0.14393.0..10.0.14393.5648
Microsoft Windows Server 2016 (Server Core installation) lt 10.0.14393.0..10.0.14393.5648
Microsoft Windows 8.1 lt 6.3.0..6.3.9600.20778
Microsoft Windows Server 2012 R2 lt 6.3.9600.0..6.3.9600.20778
Microsoft Windows Server 2012 R2 (Server Core installation) lt 6.3.9600.0..6.3.9600.20778
Fixed in: Microsoft Windows 10 Version 1809 10.0.17763.3887
Microsoft Windows Server 2019 10.0.17763.3887
Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.3887
Microsoft Windows Server 2022 10.0.20348.1487
Microsoft Windows 10 Version 20H2 10.0.19042.2486
Microsoft Windows 11 version 21H2 10.0.22000.1455
Microsoft Windows 10 Version 21H2 10.0.19044.2486
Microsoft Windows 11 version 22H2 10.0.22621.1105
Microsoft Windows 10 Version 22H2 10.0.19045.2486
Microsoft Windows 10 Version 1507 10.0.10240.19685
Microsoft Windows 10 Version 1607 10.0.14393.5648
Microsoft Windows Server 2016 10.0.14393.5648
Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.5648
Microsoft Windows 8.1 6.3.9600.20778
Microsoft Windows Server 2012 R2 6.3.9600.20778
Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.20778

Not sure whether and how you are affected? Ask a question about this vulnerability

Metrics

8.8

Priority

XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

Source: NVD, CVSS v3

8.8

CVSS v3

Severity High on the scale from 0 to 10.

Source: pwn.watch, CVE.org

34.2 %

EPSS score

Elevated — model estimates 10-50% exploitation likelihood.

Source: FIRST EPSS, percentile 98.4

Show all metrics

Severity: Critical
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 223.46 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: actively exploited
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 8.8 Methodology
CVSS v3 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 8.8
EPSS score The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“. Read in glossary: 34.2 %; Elevated — model estimates 10-50% exploitation likelihood.
EPSS percentile The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking. Read in glossary: 98.4; Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: Actively exploited
Published: 10.01.2023
In CISA KEV since The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: 10.01.2023
CISA assessment (SSVC): Exploitation: active · not automatable · Technical impact: total; Source: CISA Vulnrichment, as of 24 July 2024
CWE CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect. Read in glossary: CWE-416

Response and mitigation

Why act now?

Prioritisation rationale

This flaw was added to KEV on its disclosure day as an exploited zero-day. Any low-privileged local user can reach SYSTEM without user interaction, and the changed scope makes it suitable for escaping sandboxed processes. Attackers use it as the second stage of a chain, turning a constrained foothold from a browser exploit or phishing payload into full control of the endpoint. CISA lists no known ransomware use, but exploitation likelihood is rated very high and the patch has been available for a long time. Treat it as high priority wherever you run large client fleets, terminal servers or VDI, and expect any remaining unpatched hosts to be flagged as a clear patch-management gap in a NIS2 audit.

01
Runbook step 1
Immediate response (0-24 h)
- Deploy the January 2023 security update (Patch Tuesday, 2023-01-10) or any later cumulative update. Minimum builds: Windows 10 1507 → 10.0.10240.19685, 1607 → 10.0.14393.5648, 1809 → 10.0.17763.3887, 20H2 → 10.0.19042.2486, 21H2 → 10.0.19044.2486, 22H2 → 10.0.19045.2486; Windows 11 21H2 → 10.0.22000.1455, 22H2 → 10.0.22621.1105. Look up the KB number for each build in the Microsoft Security Update Guide.
- Find unpatched hosts via Intune, SCCM/MECM or EDR by querying for builds below these thresholds, e.g. DeviceInfo | where OSBuild < 19044.2486, adjusted per branch. Patch admin workstations, jump hosts and RDS/VDI hosts first.
- Fast-track multi-user systems: Terminal servers, Citrix/AVD session hosts and kiosks are the highest-value targets, because any logged-on standard user on them can reach SYSTEM.
- Contain unsupported builds: Restrict network access for EOL feature releases that cannot receive the fix, and schedule their replacement.
- Hunt retroactively on endpoints that stayed unpatched after January 2023 and also have browser or Office exploit alerts on record (see Detection rules).
02
Runbook step 2
Mitigation layers
- No vendor workaround exists: ALPC is core Windows IPC and cannot be disabled. Compensating controls therefore focus on preventing initial code execution and limiting what an attacker can do with SYSTEM.
- Application control: Enforce WDAC or AppLocker to block unsigned binaries and DLLs from user-writable paths (%TEMP%, %APPDATA%, Downloads, C:\Users\Public). Local exploits almost always drop their own payload.
- Attack surface reduction: Enable the Defender ASR rules "Block executable files from running unless they meet a prevalence, age, or trusted list criterion", "Block credential stealing from LSASS", and the Office/script rules. Keep browsers current with their sandbox enabled, since ALPC LPEs are typically used as sandbox escapes in exploit chains.
- IAM / least privilege: Manage local admin accounts with Windows LAPS, enforce admin tiering so no domain admins log on to clients, and enable Credential Guard so that SYSTEM access doesn't directly yield reusable domain credentials.
- Network segmentation: Block client-to-client SMB (445/tcp), RPC (135/tcp), WinRM (5985/5986/tcp) and RDP (3389/tcp) via host firewall GPO to slow lateral movement after an escalation.
- EDR tamper protection: Enforce it, because attackers with SYSTEM routinely try to disable security tooling first.
03
Runbook step 3
Detection rules
- Integrity-level jump in process ancestry (EDR / Sysmon EID 1): A Low- or Medium-integrity parent spawns a SYSTEM-integrity child outside normal service or UAC paths. KQL: DeviceProcessEvents | where InitiatingProcessIntegrityLevel in ("Low","Medium") and ProcessIntegrityLevel == "System" and InitiatingProcessFileName !in~ ("services.exe","svchost.exe","consent.exe")
- SYSTEM shells from user context (Security 4688 / Sysmon EID 1): cmd.exe, powershell.exe, pwsh.exe or rundll32.exe running as NT AUTHORITY\SYSTEM with a parent image under \Users\ or a browser/Office process. Sigma shape: selection: IntegrityLevel: System, ParentImage|contains: '\Users\'.
- Low-prevalence binaries in user paths (Sysmon EID 11 then EID 1): Newly written EXE or DLL files in %TEMP% or %APPDATA% that execute within minutes of being written.
- Failed-exploit crash artefacts (Application 1000/1001, WER): Clusters of crashes in system processes or RPC services on a single client, correlated with recent user activity.
- Post-escalation behaviour: New services (System 7045, Security 4697), LSASS access (Sysmon EID 10 with TargetImage lsass.exe), and Defender configuration changes (Defender 5001/5007).

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

Windows Advanced Local Procedure Call (ALPC) Elevation of Privilege Vulnerability

Source: pwn.watch, NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
Microsoft	Windows 10 Version 1507	`10.0.10240.0 – < 10.0.10240.19685`	`10.0.10240.19685`
Microsoft	Windows 10 Version 1607	`10.0.14393.0 – < 10.0.14393.5648`	`10.0.14393.5648`
Microsoft	Windows 10 Version 1809	`10.0.17763.0 – < 10.0.17763.3887`	`10.0.17763.3887`
Microsoft	Windows 10 Version 20H2	`10.0.0 – < 10.0.19042.2486`	`10.0.19042.2486`
Microsoft	Windows 10 Version 21H2	`10.0.19043.0 – < 10.0.19044.2486`	`10.0.19044.2486`
Microsoft	Windows 10 Version 22H2	`10.0.19045.0 – < 10.0.19045.2486`	`10.0.19045.2486`
Microsoft	Windows 11 version 21H2	`10.0.0 – < 10.0.22000.1455`	`10.0.22000.1455`
Microsoft	Windows 11 version 22H2	`10.0.22621.0 – < 10.0.22621.1105`	`10.0.22621.1105`
Microsoft	Windows 8.1	`6.3.0 – < 6.3.9600.20778`	`6.3.9600.20778`
Microsoft	Windows Server 2012 R2	`6.3.9600.0 – < 6.3.9600.20778`	`6.3.9600.20778`
Microsoft	Windows Server 2012 R2 (Server Core installation)	`6.3.9600.0 – < 6.3.9600.20778`	`6.3.9600.20778`
Microsoft	Windows Server 2016	`10.0.14393.0 – < 10.0.14393.5648`	`10.0.14393.5648`
Microsoft	Windows Server 2016 (Server Core installation)	`10.0.14393.0 – < 10.0.14393.5648`	`10.0.14393.5648`
Microsoft	Windows Server 2019	`10.0.17763.0 – < 10.0.17763.3887`	`10.0.17763.3887`
Microsoft	Windows Server 2019 (Server Core installation)	`10.0.17763.0 – < 10.0.17763.3887`	`10.0.17763.3887`
Microsoft	Windows Server 2022	`10.0.20348.0 – < 10.0.20348.1487`	`10.0.20348.1487`

Vendors and products

Affected operating systems

Affected operating systems

Windows	microsoft	windows_10_1507	—
Windows	microsoft	windows_10_1607	—
Windows	microsoft	windows_10_1809	—
Windows	microsoft	windows_10_20h2	—
Windows	microsoft	windows_10_21h2	—
Windows	microsoft	windows_10_22h2	—
Windows	microsoft	windows_11_21h2	—
Windows	microsoft	windows_11_22h2	—
Windows	microsoft	windows_rt_8.1	—
Windows	microsoft	windows_server_2012	`r2`
Windows	microsoft	windows_server_2016	—
Windows	microsoft	windows_server_2019	—
Windows	microsoft	windows_server_2022	—

Weakness classes (CWE)

CWE-416Use After Free
Variant
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
Entry at MITRE CWE-416

Public exploit references

Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

Public exploit references

CISA KEV Catalog	CISA Known Exploited Vulnerability (opens in a new tab)cisa.gov	actively exploited	10.01.2023

References & sources

Microsoft Security Update GuideWindows Advanced Local Procedure Call (ALPC) Elevation of Privilege VulnerabilityVendor advisory, Patch, Vendor advisory
cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2023-21674government-resource, US government resource
pwn.watchpwn.watch: Microsoft Windows: Advanced Local Procedure Call (ALPC) Privilege Escalation (CVE-2023-21674)pwn-watch
Microsoft Security Update GuideVendor advisory: Microsoft Windowspwn-watch
NVD (NIST)NVD: CVE-2023-21674pwn-watch
cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch

Embed badge

Show the severity and KEV status of this vulnerability on your site – with a link back here. The image is updated hourly.

<a href="https://intel.neosec.eu/en/cve/CVE-2023-21674"><img src="https://intel.neosec.eu/badge/cve/CVE-2023-21674.svg?lang=en" alt="CVE-2023-21674 – NEOSEC Intel" height="20"></a>

What is affected, what to do

Metrics

Response and mitigation

Prioritisation rationale

Immediate response (0-24 h)

Mitigation layers

Detection rules

Detection rules

Classification under NIS2 and CRA

Description

Affected products

Vendors and products

Affected operating systems

Weakness classes (CWE)

Public exploit references

References & sources