CVE-2026-48576: Windows 10 1607 Auth Bypass Vulnerability

CVE-2026-48576 Overview

CVE-2026-48576 is a protection mechanism failure in Windows Secure Boot that allows an authorized attacker to bypass a security feature locally. The flaw is tracked under [CWE-1329] (Reliance on Component That is Not Updateable) and affects a broad range of Windows client and server releases. An attacker with high privileges on the local system can subvert the Secure Boot integrity guarantee that protects the early boot chain. Microsoft has assigned this issue a high severity rating and published guidance through the Microsoft Security Response Center.

Critical Impact
A local attacker with administrative privileges can bypass Secure Boot, undermining boot-time integrity verification and enabling persistence below the operating system.

Affected Products

Microsoft Windows 10 (1607, 1809, 21H2, 22H2) across x86, x64, and arm64 builds
Microsoft Windows 11 (23H2, 24H2, 25H2, 26H1) across x64 and arm64 builds
Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025

Discovery Timeline

2026-06-09 - CVE-2026-48576 published to the National Vulnerability Database
2026-06-10 - Record last modified in NVD

Technical Details for CVE-2026-48576

Vulnerability Analysis

Secure Boot is the Unified Extensible Firmware Interface (UEFI) feature that validates each boot component against signatures stored in firmware. CVE-2026-48576 represents a Secure Boot bypass in which the trust chain can be circumvented by an authorized local attacker. The flaw is classified as a protection mechanism failure, meaning the verification logic exists but can be defeated under specific conditions. Successful exploitation breaks the assumption that only signed and trusted code executes before the Windows kernel loads.

The vulnerability impacts confidentiality and integrity at a high level and crosses a security scope boundary, since firmware-level trust governs the entire operating system. Microsoft has not reported active exploitation, and no public proof-of-concept exists at this time.

Root Cause

The issue maps to [CWE-1329], indicating reliance on a component that cannot be readily updated. In Secure Boot bypass scenarios of this class, the weakness typically resides in revocation handling, signature validation, or in shim and bootloader components covered by the Secure Boot policy. Because the trust anchor lives in firmware variables and the UEFI revocation list, remediating the underlying weakness requires coordinated updates to both the operating system and protected boot artifacts.

Attack Vector

Exploitation requires local access and high privileges on the target system. An attacker who already holds administrative rights can stage a vulnerable or unrevoked boot component, modify Secure Boot related variables, or chain another flaw to disable validation during the next boot. The result is the ability to load unsigned or attacker-controlled code into the pre-kernel environment, enabling bootkit-style persistence and tamper-resistant footholds. User interaction is not required.

No verified exploit code is available. Refer to the Microsoft Security Update Guide entry for CVE-2026-48576 for technical specifics released by the vendor.

Detection Methods for CVE-2026-48576

Indicators of Compromise

Unexpected modifications to UEFI variables such as db, dbx, KEK, or PK outside of authorized update windows.
Presence of bootloaders, shim binaries, or EFI applications in the EFI System Partition that do not match the vendor-signed baseline.
Secure Boot state reporting as enabled while measured boot logs show unexpected PCR values or unknown loaded images.

Detection Strategies

Validate Secure Boot status with Confirm-SecureBootUEFI and compare measured boot logs against a known-good baseline across the fleet.
Monitor for administrative actions that touch bcdedit, mountvol, or the EFI System Partition, since legitimate Secure Boot bypass requires staging files in privileged locations.
Correlate firmware attestation data, where available through TPM-backed remote attestation, to flag endpoints whose boot measurements deviate after patching.

Monitoring Recommendations

Ingest Windows Defender System Guard runtime attestation events and Microsoft-Windows-TPM-WMI logs into the SIEM for boot-integrity baselining.
Alert on creation or modification of .efi files under \EFI\Microsoft\Boot\ and on writes to the EFI System Partition outside vendor update workflows.
Track installation status of the June 2026 Microsoft security updates across Windows 10, Windows 11, and Windows Server estates to identify unpatched hosts.

How to Mitigate CVE-2026-48576

Immediate Actions Required

Apply the Microsoft security update referenced in the MSRC advisory for CVE-2026-48576 to all affected Windows 10, Windows 11, and Windows Server systems.
Restrict and audit local administrator accounts, since exploitation requires high local privileges.
Enforce BitLocker with TPM and PIN protection so that offline tampering with the EFI System Partition triggers recovery.

Patch Information

Microsoft has released fixes through its standard security update channel. Consult the Microsoft Security Update Guide entry for CVE-2026-48576 for the specific KB articles and cumulative updates that apply to each affected build, including Windows Server 2012 through Server 2025 and all listed Windows 10 and Windows 11 versions. After installation, some Secure Boot revocations may require a follow-up step to update the UEFI forbidden signatures database (dbx).

Workarounds

Limit physical and remote administrative access to endpoints, since exploitation requires an authenticated local attacker with elevated rights.
Enable Virtualization-Based Security (VBS) and Hypervisor-Protected Code Integrity (HVCI) to raise the cost of bootkit-style follow-on activity.
Use TPM-backed remote attestation and conditional access to deny network resources to devices whose boot integrity cannot be verified.

bash

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