Windows 10 1607: Local privilege escalation in SysMain service
Summary
Windows 10 version 1607 and Windows Server 2016 contain an out-of-bounds read in the Windows SysMain service. An authorized local user can exploit it to elevate privileges, with high impact on confidentiality, integrity and availability. CISA's SSVC assessment lists no exploitation and marks the flaw as not automatable.
Affected
- Microsoft Windows 10 Version 1607 (builds below 10.0.14393.9612)
- Microsoft Windows Server 2016 and Server Core installation (builds below 10.0.14393.9612)
Fixed in
- Build 10.0.14393.9612 or later, according to the CNA data.
- Secondary sources name KB5126868 as the fix, but this mapping is not confirmed on the MSRC page. Verify it before rollout.
Workaround
- Unknown. No vendor workaround was identified; apply the update.
Exploitation
- No public exploitation or proof of concept identified at the time of analysis.
- CISA SSVC: exploitation none, automatable no, technical impact total.
Our recommendation
- Verify the KB for CVE-2026-96306 in the MSRC Security Updates table, then apply the October 2026 cumulative update to Windows 10 1607 and Server 2016.
- Confirm ESU eligibility for Windows 10 1607 and the end-of-support status of Server 2016 with Microsoft.
- Review the reported Exchange mail issue after KB5126868 before rollout.
- Restrict local logon to trusted users on affected systems and monitor for unexpected privilege changes.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Elevation of privilege – Windows Sysmain Service
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Windows, Windows ESU (Extended Security Updates)
- Updates (KB)
- KB5126868, KB5126651, KB5126657, KB5126653, KB5127648, KB5127646
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- MSRC Security Update Guide: CVE-2026-96306 msrc.microsoft.com
- Vulners: CVE-2026-96306 vulners.com
- Microsoft Update Catalog: KB5126868 www.catalog.update.microsoft.com
- Microsoft Learn: Windows 10 1607 and Server 2016 release health learn.microsoft.com
- AskWoody: October 2026 Windows patches out www.askwoody.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, 00:55.
Original description (NVD)
Out-of-bounds read in Windows Sysmain Service 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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