CVE-2026-48570: Windows 10 1607 Auth Bypass Vulnerability

CVE-2026-48570 Overview

CVE-2026-48570 is a protection mechanism failure [CWE-693] in Windows Secure Boot. An authorized local attacker can bypass a security feature on affected Windows client and server systems. The flaw carries a CVSS 3.1 score of 7.9 and affects a broad range of supported Windows builds, from Windows 10 1607 through Windows 11 26H1 and from Windows Server 2012 through Windows Server 2025. Microsoft published the advisory through MSRC, and the issue was added to the NVD on June 9, 2026.

Critical Impact
A local attacker with high privileges can bypass Secure Boot, undermining the firmware-to-OS trust chain and enabling persistence below the operating system on affected Windows and Windows Server releases.

Affected Products

Microsoft Windows 10 (1607, 1809, 21H2, 22H2) across x86, x64, and ARM64
Microsoft Windows 11 (23H2, 24H2, 25H2, 26H1) across x64 and ARM64
Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025

Discovery Timeline

2026-06-09 - CVE-2026-48570 published to NVD
2026-06-10 - Last updated in NVD database
2026-06-11 - EPSS scoring recorded for CVE-2026-48570

Technical Details for CVE-2026-48570

Vulnerability Analysis

CVE-2026-48570 is classified as a Secure Boot bypass caused by a protection mechanism failure [CWE-693]. Secure Boot is a UEFI feature that verifies the cryptographic signature of bootloaders, drivers, and the Windows kernel before execution. When Secure Boot operates correctly, only firmware images signed by trusted authorities are allowed to load. A failure in this protection mechanism breaks that guarantee.

Microsoft scopes the issue as a local security feature bypass requiring an authorized attacker. The CVSS vector indicates the impact crosses a trust boundary, affecting confidentiality and integrity of components beyond the original scope, including pre-OS code paths. A successful bypass enables loading of code that would otherwise be rejected by the Secure Boot policy.

Root Cause

The underlying defect lies in how Windows Secure Boot validates or enforces a trust decision during the boot chain. Because the protection mechanism fails rather than producing an outright validation error, untrusted components can be permitted to execute. Microsoft has not published low-level technical details beyond the MSRC advisory, and no public proof-of-concept is available.

Attack Vector

Exploitation requires local access and high privileges, typically administrative rights on the target system. The attacker must already be authenticated and able to interact with boot configuration, EFI System Partition contents, or related Secure Boot policy stores. No user interaction is required. After the bypass, the attacker can stage a malicious bootloader or pre-OS payload that loads despite Secure Boot being enabled, establishing persistence that survives operating system reinstallation.

No verified exploitation code is publicly available. See the Microsoft Security Update Guide for vendor-supplied details.

Detection Methods for CVE-2026-48570

Indicators of Compromise

Unexpected modifications to files on the EFI System Partition, particularly \EFI\Microsoft\Boot\bootmgfw.efi and other signed boot binaries.
Changes to UEFI variables governing Secure Boot policy, such as db, dbx, KEK, or PK, outside of an authorized firmware update window.
New or modified entries in the BCD store (bcdedit /enum all) referencing unknown bootloaders or alternate EFI applications.
Measured Boot log (TCG log) entries that diverge from a known-good baseline on otherwise unchanged systems.

Detection Strategies

Compare current Secure Boot state (Confirm-SecureBootUEFI) and policy hashes against a hardware-attested baseline to flag silent policy changes.
Monitor administrative use of bcdedit, mountvol, and direct writes to the EFI System Partition for unexpected accounts or hosts.
Validate TPM-backed boot measurements through device health attestation services to surface boot integrity drift.

Monitoring Recommendations

Centralize Windows Event Log channels covering boot integrity, code integrity (Microsoft-Windows-CodeIntegrity/Operational), and TPM events for correlation.
Alert on privileged process activity touching \Device\HarddiskVolume*\EFI paths or invoking Secure Boot configuration cmdlets.
Track Microsoft patch deployment status across Windows 10, Windows 11, and Windows Server fleets to identify systems still exposed to CVE-2026-48570.

How to Mitigate CVE-2026-48570

Immediate Actions Required

Apply the Microsoft security update for CVE-2026-48570 from the Microsoft Security Update Guide to all affected Windows 10, Windows 11, and Windows Server systems.
Inventory endpoints and servers against the affected version list and prioritize patching of domain controllers, hypervisors, and other high-value hosts.
Restrict membership in local Administrators and equivalent groups, since exploitation requires high privileges on the target.
Verify Secure Boot remains enabled (Confirm-SecureBootUEFI) after patching and after any firmware update.

Patch Information

Microsoft has issued security updates addressing CVE-2026-48570 across the affected Windows client and server releases. Refer to the Microsoft Security Update Guide for the specific KB articles, applicable build numbers, and any required Secure Boot DBX revocation list updates that must accompany the OS patch.

Workarounds

Limit local logon and remote administrative access to trusted operators using Just Enough Administration and tiered admin models.
Enable BitLocker with TPM and PIN to ensure tampering with boot components triggers recovery and is visible to administrators.
Enforce device health attestation through Microsoft Intune or equivalent so non-compliant boot states are denied access to corporate resources.
Apply the latest Secure Boot DBX (forbidden signatures) updates to revoke trust in any bootloaders abused as part of this bypass.

bash

# Verify Secure Boot status and review boot configuration on Windows
powershell -Command "Confirm-SecureBootUEFI"
powershell -Command "Get-SecureBootPolicy"
bcdedit /enum all