Windows Network Load Balancing: Use-after-free leads to code execution
Summary
Use-after-free vulnerability in the Windows Network Load Balancing (NLB) component. According to the CVE record, an unauthenticated attacker on an adjacent network can execute code without user interaction. Affected are Windows 10 Version 1607 and 1809 as well as several Windows Server releases with NLB. Some third-party sources list a network vector with CVSS 9.8, so the exposure should be verified.
Affected
- Windows 10 Version 1607: 10.0.14393.0 to before 10.0.14393.9612
- Windows 10 Version 1809: 10.0.17763.0 to before 10.0.17763.9376
- Windows Server 2012 and 2012 R2 (including Server Core): before 6.2.9200.26434 and before 6.3.9600.23470
- Windows Server 2016, 2019 (including Server Core): before 10.0.14393.9612 and before 10.0.17763.9376
- Windows Server 2022: before 10.0.20348.5761
- Windows Server 2025 (including Server Core): before 10.0.26100.33650
Fixed in
- Windows 10 1607 and Server 2016: build 10.0.14393.9612 (KB5126868)
- Windows 10 1809 and Server 2019: build 10.0.17763.9376
- Windows Server 2022: build 10.0.20348.5761
- Windows Server 2025: build 10.0.26100.33650
- Windows Server 2012 and 2012 R2: builds per the CVE record (6.2.9200.26434 and 6.3.9600.23470)
- Whether Windows 10 1607 receives further updates after this build is unknown.
Workaround
Unknown.
- Not from the vendor: restrict which hosts can reach NLB virtual IPs and cluster ports, and segment the NLB subnet.
Exploitation
- CISA SSVC: Exploitation none, Automatable yes.
- No exploitation in the wild known; not listed in CISA KEV.
- No public proof of concept found.
- EPSS about 0.4 percent, low predicted exploitation probability.
Our recommendation
- Check whether NLB is in use and which hosts are affected.
- Apply the October 2026 security update to the affected systems as a high priority where NLB is used and reachable from other segments.
- Restrict access to NLB virtual IPs and cluster ports until patched.
- Verify the CVSS vector and the Windows 10 1607 lifecycle on the Microsoft pages and plan an upgrade if support has ended.
- Document systems where NLB is not used.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Remote code execution – Windows Network Load Balancing
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Windows, Windows ESU (Extended Security Updates)
- Updates (KB)
- KB5126651, KB5126655, KB5126646, KB5126868, KB5126835, KB5126836
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-83862 msrc.microsoft.com
- KB5126868: Windows 10 1607 security update support.microsoft.com
- OpenCVE: CVE-2026-83862 app.opencve.io
- Vulners NVD: CVE-2026-83862 vulners.com
- Strix: CVE-2026-83862 www.strix.ai
- VulDB: CVE-2026-83862 vuldb.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 31 Oct 2026, 18:28.
Original description (NVD)
Use after free in Windows Network Load Balancing allows an unauthorized attacker to execute code over an adjacent network.
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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