Microsoft Windows UEFI: Secure Boot security feature bypass
Summary
Microsoft has fixed a vulnerability in the UEFI firmware component of Windows. An authorized local attacker with a low-privileged account can bypass the UEFI Secure Boot security feature. No user interaction is required. Because UEFI runs before the operating system, a successful bypass can undermine boot-time protections such as BitLocker's trusted boot chain. No in-the-wild exploitation or public proof of concept is known.
Affected
- Windows 10 Version 1607 (10.0.14393.0 to below 10.0.14393.9612)
- Windows 10 Version 1809 (below 10.0.17763.9376)
- Windows 10 Version 21H2 (below 10.0.19044.7807)
- Windows 10 Version 22H2 (below 10.0.19045.7807)
- Windows 11 Version 23H2 (below 10.0.22631.7652)
- Windows 11 Version 24H2 (below 10.0.26100.9711)
- Windows 11 Version 25H2 (below 10.0.26200.9711)
- Windows 11 Version 26H1 (below 10.0.28000.3231)
- Windows 11 Version 26H2 (below 10.0.26300.9711)
- Windows Server 2012 and 2012 R2 (below 6.2.9200.26434 and 6.3.9600.23470)
- Windows Server 2016 (below 10.0.14393.9612)
Fixed in
- Windows 10 Version 1607 and Windows Server 2016: 10.0.14393.9612
- Windows 10 Version 1809: 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 and 26H2: 10.0.26200.9711 and 10.0.26300.9711
- Windows 11 Version 26H1: 10.0.28000.3231
- Windows Server 2012 and 2012 R2: 6.2.9200.26434 and 6.3.9600.23470
- Knowledge base numbers: KB5126651 (Windows 10 1809, Server 2019), KB5126653 (Windows 11 23H2), KB5126646 (Windows Server 2025). No KB for Windows 10 1607 confirmed; check the MSRC Security Update Guide.
Workaround
No workaround documented. Installing the vendor update is the mitigation.
- Verify that Secure Boot is enabled and enforced on all managed Windows systems.
Exploitation
- CISA SSVC assessment: exploitation none, not automatable, total technical impact.
- Not listed in CISA KEV.
- No public proof of concept found; this does not prove none exists.
- No reports of exploitation in the wild found.
Our recommendation
- Inventory all Windows systems, including Windows 10 1607 and Server 2016, and check their build numbers.
- Install the fixed cumulative update for each version as listed above.
- Confirm that Windows 10 1607 still receives security updates or whether Extended Security Updates are required.
- Verify Secure Boot status across the fleet and monitor for firmware or boot-chain integrity alerts.
- Priority is high for systems still on Windows 10 1607 or Server 2016 and for devices relying on Secure Boot; medium for fully patched fleets.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Security feature bypass – Windows UEFI
- 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-2026-49785 msrc.microsoft.com
- SentinelOne vulnerability database: CVE-2026-49785 www.sentinelone.com
- Vulners: CVE-2026-49785 (CVE record) vulners.com
- Vulners: CVE-2026-49785 (CVElist) vulners.com
- Vulners: MSRC data for CVE-2026-49785 vulners.com
- Strix: CVE-2026-49785 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, 04:58.
Original description (NVD)
Improper resource shutdown or release in Windows UEFI allows an authorized attacker to bypass a security feature 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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