CVE-2021-36276: Dell DBUtilDrv2.sys Privilege Escalation

CVE-2021-36276 Overview

CVE-2021-36276 is an insufficient access control vulnerability in the Dell DBUtilDrv2.sys driver, affecting versions 2.5 and 2.6. The driver ships with Dell client platform firmware update utilities and exposes privileged operations to unprivileged callers. A local authenticated user can abuse the driver to escalate privileges, cause denial of service, or disclose kernel information. The flaw is classified under [CWE-285] Improper Authorization.

Critical Impact

Local authenticated attackers can leverage the signed DBUtilDrv2.sys driver to gain SYSTEM-level privileges on affected Windows endpoints, enabling full compromise of confidentiality, integrity, and availability.

Affected Products

• Dell DBUtilDrv2.sys driver version 2.5
• Dell DBUtilDrv2.sys driver version 2.6
• Dell client platforms shipping the affected firmware update utility

Discovery Timeline

• 2021-08-09 - CVE-2021-36276 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-36276

Vulnerability Analysis

The DBUtilDrv2.sys kernel driver is distributed by Dell to support firmware and BIOS update operations. The driver registers IOCTL handlers that perform privileged kernel operations, including arbitrary memory read and write primitives. The vulnerability stems from the driver failing to restrict access to these IOCTL handlers based on caller privileges or integrity level.

A local authenticated user can open a handle to the driver device and issue IOCTL requests that the driver will service without verifying authorization. Because the driver runs in kernel mode and is signed by Dell, calls executed through it bypass user-mode privilege boundaries. This enables an attacker to read sensitive kernel memory, write to arbitrary kernel addresses, or trigger conditions that crash the system.

The issue is tracked as [CWE-285] Improper Authorization. It is functionally similar to other vulnerable driver classes that have been weaponized in Bring Your Own Vulnerable Driver (BYOVD) attacks.

Root Cause

The root cause is missing authorization checks on the IOCTL dispatch routines exposed by DBUtilDrv2.sys. The driver creates a device object accessible to non-administrative users and does not validate the requester's security context before performing privileged memory operations.

Attack Vector

Exploitation requires local authenticated access to a Windows endpoint where DBUtilDrv2.sys is loaded or where an attacker can load the signed driver. The attacker opens a handle to the driver's device object and issues crafted IOCTL requests to invoke the privileged primitives. No user interaction is required beyond the initial local logon. Refer to the Dell Security Advisory DSA-2021-152 for vendor technical details.

Detection Methods for CVE-2021-36276

Indicators of Compromise

• Presence of DBUtilDrv2.sys versions 2.5 or 2.6 on disk, particularly in user-writable directories or temporary paths.
• Unexpected service or driver load events referencing DBUtilDrv2 from non-Dell update workflows.
• Creation of the driver's device object handle by processes unrelated to Dell firmware utilities.

Detection Strategies

• Hunt for kernel driver load events (Windows Event ID 6 in Sysmon) where the image name matches DBUtilDrv2.sys and the file hash corresponds to the vulnerable versions.
• Monitor for CreateFile calls targeting the driver's named device object followed by DeviceIoControl invocations from non-Dell processes.
• Correlate driver loads with subsequent token manipulation, process privilege changes, or LSASS access events.

Monitoring Recommendations

• Enable Microsoft's vulnerable driver blocklist and Windows Defender Application Control (WDAC) policies to log and block loads of known-vulnerable drivers.
• Forward kernel driver load telemetry and Sysmon events to a centralized SIEM for retrospective hunting.
• Maintain an inventory of installed Dell client utilities and flag systems still carrying legacy DBUtilDrv2.sys builds.

How to Mitigate CVE-2021-36276

Immediate Actions Required

• Inventory all endpoints for DBUtilDrv2.sys versions 2.5 and 2.6 and remove or replace the vulnerable binary.
• Apply the remediation steps outlined in Dell Security Advisory DSA-2021-152.
• Enable the Microsoft recommended driver blocklist on Windows 10, Windows 11, and Windows Server systems.

Patch Information

Dell published Dell Security Advisory DSA-2021-152, which provides updated Dell client platform firmware update utilities containing a patched DBUtilDrv2.sys driver. Administrators should apply the fixed Dell client utilities and remove any cached copies of the vulnerable driver from endpoints.

Workarounds

• Remove the DBUtilDrv2.sys file from affected systems if firmware update utilities are not actively required.
• Restrict local logon rights and enforce least privilege to limit which users can interact with kernel device objects.
• Deploy Windows Defender Application Control or Hypervisor-Protected Code Integrity (HVCI) with the Microsoft vulnerable driver blocklist enabled.

# Example: enumerate and remove the vulnerable driver on Windows (PowerShell)
Get-ChildItem -Path C:\ -Recurse -Filter DBUtilDrv2.sys -ErrorAction SilentlyContinue |
    ForEach-Object {
        Write-Host "Found: $($_.FullName) Version: $($_.VersionInfo.FileVersion)"
        Remove-Item -Path $_.FullName -Force
    }

# Verify Microsoft vulnerable driver blocklist is enabled
Get-MpPreference | Select-Object -Property AttackSurfaceReductionRules_Ids