Windows ReFS: Heap-based buffer overflow enables local privilege escalation
Summary
A heap-based buffer overflow in the Windows Resilient File System (ReFS) allows an authorized local user to elevate privileges. Exploitation requires local access and a valid low-privilege account on the system, so the risk is mainly on multi-user systems and file servers. Microsoft has released fixes for the affected Windows versions.
Affected
- Windows 10 Version 1607 and Windows Server 2016: builds below 10.0.14393.9612
- Windows 10 Version 1809 and Windows Server 2019: builds below 10.0.17763.9376
- Windows 10 Version 21H2: builds below 10.0.19044.7807
- Windows 10 Version 22H2: builds below 10.0.19045.7807
- Windows 11 Version 23H2: builds below 10.0.22631.7652
- Windows 11 Version 24H2: builds below 10.0.26100.9711
- Windows 11 Version 25H2: builds below 10.0.26200.9711
- Windows 11 Version 26H1: builds below 10.0.28000.3231
- Windows 11 Version 26H2: builds below 10.0.26300.9711
- Windows Server 2022: builds below 10.0.20348.5761
Fixed in
- Windows 10 Version 1607 and Windows Server 2016: 10.0.14393.9612
- Windows 10 Version 1809 and Windows Server 2019: 10.0.17763.9376
- Windows 10 Version 21H2: 10.0.19044.7807
- Windows 10 Version 22H2: 10.0.19045.7807
- Windows 11 Version 23H2: 10.0.22631.7652
- Windows 11 Version 24H2: 10.0.26100.9711
- Windows 11 Version 25H2: 10.0.26200.9711
- Windows 11 Version 26H1: 10.0.28000.3231
- Windows 11 Version 26H2: 10.0.26300.9711
- Windows Server 2022: 10.0.20348.5761
- KB article numbers: see the MSRC update guide.
Workaround
Unknown.
- No workaround or mitigation was found in the sources reviewed. Applying the vendor patch is the fix.
Exploitation
- Not listed in CISA KEV.
- CISA SSVC assessment: exploitation none, not automatable, total technical impact.
- EPSS score 0.00341 (below 1%).
- No public proof-of-concept found in the sources checked. This does not rule out that one exists.
Our recommendation
- Identify Windows 10 1607 hosts first, especially those using ReFS or allowing multiple local users.
- Install the fixed build for each affected version, or upgrade unsupported systems.
- Review local account hygiene and limit low-privilege accounts on shared systems and file servers.
- Confirm KB numbers and details on the MSRC page before rollout.
- Re-check public exploit sources before the patch deadline.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Elevation of privilege – 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)
- KB5127648, KB5126651, KB5126655, KB5126657, KB5126646, KB5126653
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-70048 msrc.microsoft.com
- Microsoft Security Update Guide (en-US): CVE-2026-70048 msrc.microsoft.com
- NVD record via Vulners: CVE-2026-70048 vulners.com
- OpenCVE: CVE-2026-70048 app.opencve.io
- Vulners MSCVE: MS:CVE-2026-70048 vulners.com
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, 04:28.
Original description (NVD)
Heap-based buffer overflow in Windows Resilient File System (ReFS) allows an authorized attacker to elevate privileges 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.
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