Microsoft Windows: Heap-based buffer overflow in ReFS allows local code execution
Summary
A heap-based buffer overflow in the Windows Resilient File System (ReFS) allows an authorized local attacker to execute code. The attacker first needs a valid low-privileged account or foothold on the system, and no user interaction is required. The CNA rates the impact as high for confidentiality, integrity and availability. The MSRC title says 'Remote Code Execution', but the description and CVSS vector describe a local attack, and this entry follows the description.
Affected
- Windows 10 Version 1607 and Windows Server 2016 (including Server Core): before 10.0.14393.9612
- Windows 10 Version 1809 and Windows Server 2019 (including Server Core): before 10.0.17763.9376
- Windows 10 Version 21H2: before 10.0.19044.7807
- Windows 10 Version 22H2: before 10.0.19045.7807
- Windows 11 Version 23H2: before 10.0.22631.7652
- Windows 11 Version 24H2 and 25H2: before 10.0.26100.9711 and 10.0.26200.9711
- Windows 11 Version 26H1: before 10.0.28000.3231
- Windows 11 Version 26H2: before 10.0.26300.9711
- Windows Server 2022: before 10.0.20348.5761
Fixed in
- October 2026 cumulative updates (per Tenable plugin pages): KB5126868 for Windows 10 1607 and Server 2016, KB5126657 for Windows 10 21H2 and 22H2, KB5127648 for Windows 11 24H2 and 25H2, KB5126646 for Windows Server 2025
- Verify the build numbers on the MSRC page before deployment.
Workaround
Unknown. No vendor-documented interim mitigation was found. Apply the patch.
Exploitation
- No evidence of active exploitation found in the research. CISA SSVC: exploitation none, not automatable.
- No public proof-of-concept found.
- EPSS 0.00318 (low).
- CISA KEV status was not checked.
Our recommendation
- Identify hosts running the affected builds and prioritize multi-user systems, file servers, RDS/terminal servers and older 1607/2016 hosts.
- Install the October 2026 cumulative update.
- Limit local logon to necessary accounts and monitor for privilege escalation.
- Check whether ReFS is used at all.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Remote code execution – Windows Resilient File System (ReFS)
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Windows, Windows ESU (Extended Security Updates)
- Updates (KB)
- KB5126657, KB5126655, KB5126653, KB5127648, KB5126646, KB5127646
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- MSRC Security Update Guide: CVE-2026-102227 msrc.microsoft.com
- Vulners: NVD record CVE-2026-102227 vulners.com
- Vulners: CVE List record CVE-2026-102227 vulners.com
- Tenable Nessus plugin 365467 (Oct 2026 update for Windows 10 21H2/22H2) www.tenable.com
- Strix: CVE-2026-102227 www.strix.ai
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 2 Nov 2026, 05:08.
Original description (NVD)
Heap-based buffer overflow in Windows Resilient File System (ReFS) allows an authorized attacker to execute code locally.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
Affected? We can help.
We check whether your systems are affected, install updates and close the gap – continuously with the System Health Checker if you wish.