CVE-2021-3809: HP Elite Dragonfly Firmware RCE Vulnerability

CVE-2021-3809 Overview

CVE-2021-3809 is a BIOS/UEFI firmware vulnerability affecting a wide range of HP PC products that could allow arbitrary code execution. The vulnerability exists within the UEFI firmware layer, which operates at a privileged level below the operating system. An attacker with local access and low-level privileges could potentially exploit this flaw to execute arbitrary code, compromising the integrity, confidentiality, and availability of the affected system.

This vulnerability is particularly concerning because firmware-level attacks can persist across operating system reinstallations and may be difficult to detect using traditional security tools. HP has released firmware updates to address this security issue across multiple product lines.

Critical Impact

Successful exploitation enables arbitrary code execution at the firmware level, potentially allowing attackers to establish persistent access, bypass security controls, and compromise system integrity below the operating system layer.

Affected Products

• HP Elite Dragonfly (Firmware version 01.12.00)
• HP EliteBook Series (1040 G4, 1050 G1, 725 G4, 735 G5/G6, 745 G4/G5/G6, 755 G4/G5, 820 G4, 828 G4, 830 G5/G6, 836 G5/G6, 840 G4/G5/G6, 840r G4, 846 G5, 848 G4, 850 G4/G5/G6, X360 variants)
• HP ProBook Series (11 EE G2, 430 G4/G5/G6, 440 G4/G5/G6, 445 G6, 445r G6, 450 G4/G5/G6, 455 G4/G5/G6, 455r G6, 470 G4/G5, 640 G3/G4/G5, 645 G3/G4, 650 G3/G4/G5, 655 G3, X360 variants)
• HP ZBook Series (14u G4/G5/G6, 15 G4/G5/G6, 15u G4/G5/G6, 17 G4/G5/G6, Studio G4/G5, Studio X360 G5, X2 G4)
• HP EliteDesk/ProDesk Series (705 G3/G4/G5, 800 G3/G4/G5, 880 G3/G4/G5, 400 G3/G4/G5/G6, 405 G4, 480 G4/G5/G6, 600 G3/G4/G5, 680 G3/G4)
• HP Z Workstation Series (Z1 All-in-One G3, Z1 Entry Tower G5, Z2 Mini G3/G4/G5, Z2 SFF G4/G5, Z2 Tower G4/G5, Z238 Microtower, Z240 SFF/Tower)
• HP Retail Systems (Elite Slice G1/G2, Engage Flex Pro, Engage Go, Engage One, MP9 G4)

Discovery Timeline

• February 1, 2023 - CVE-2021-3809 published to NVD
• March 27, 2025 - Last updated in NVD database

Technical Details for CVE-2021-3809

Vulnerability Analysis

This vulnerability resides in the BIOS (UEFI Firmware) of numerous HP PC products. The flaw falls under CWE-269 (Improper Privilege Management), indicating that the vulnerability involves inadequate control over privileged operations within the firmware environment.

UEFI firmware operates at Ring -2 privilege level, below even the operating system kernel. Exploitation of this vulnerability requires local access to the system with low-level privileges. Once exploited, an attacker can achieve arbitrary code execution within the firmware context, which provides several concerning capabilities including the ability to modify boot processes, install persistent implants that survive OS reinstallation, and potentially disable security features such as Secure Boot.

The attack does not require user interaction, and the scope remains unchanged from the vulnerable component, meaning the impact is contained to the affected system's confidentiality, integrity, and availability—all of which can be fully compromised.

Root Cause

The root cause stems from improper privilege management within the HP UEFI firmware implementation. The specific technical details of the vulnerability have not been publicly disclosed by HP beyond the classification as enabling arbitrary code execution. The vulnerability likely involves insufficient validation or access controls within firmware system management mode (SMM) handlers or other privileged firmware components that could be abused by a local attacker.

Attack Vector

The attack requires local access to the target system. An attacker with low-privilege access to the operating system could potentially exploit this vulnerability through:

1. Gaining initial access to the target system through phishing, credential theft, or another attack vector
2. Escalating access to interact with UEFI firmware interfaces
3. Exploiting the firmware vulnerability to achieve arbitrary code execution
4. Installing persistent firmware-level malware or backdoors

The local attack vector and low privilege requirement indicate that the vulnerability can be triggered from within a standard user context, making it accessible to any attacker who has achieved initial system compromise.

Detection Methods for CVE-2021-3809

Indicators of Compromise

• Unexpected modifications to UEFI firmware or NVRAM variables
• Anomalous SMM (System Management Mode) activity or unexpected SMI (System Management Interrupt) generation
• Changes to Secure Boot configuration or disabled security features without administrator action
• Unexplained boot process modifications or unauthorized boot loader changes

Detection Strategies

• Implement firmware integrity monitoring using tools that can verify UEFI firmware against known-good baselines
• Enable and monitor Secure Boot logs for unauthorized modification attempts
• Deploy endpoint detection and response (EDR) solutions with firmware-level visibility
• Perform regular firmware version audits to ensure all systems are running patched versions

Monitoring Recommendations

• Configure hardware security module (HSM) or TPM-based attestation to detect firmware tampering
• Monitor system event logs for BIOS/UEFI update attempts outside of scheduled maintenance windows
• Implement asset inventory tracking to identify all HP devices running vulnerable firmware versions
• Enable HP Sure Start or similar firmware protection technologies where available

How to Mitigate CVE-2021-3809

Immediate Actions Required

• Inventory all HP PC products in your environment to identify affected systems
• Prioritize firmware updates for systems with sensitive data or critical business functions
• Restrict local access to affected systems until firmware updates can be applied
• Enable BIOS administrator passwords to prevent unauthorized firmware modifications

Patch Information

HP has released firmware updates to mitigate this vulnerability. Organizations should download and apply the appropriate BIOS/UEFI firmware update for each affected product from the HP Support Advisory. The security bulletin HPSBHF03788 provides a comprehensive list of affected products with their corresponding patched firmware versions.

Firmware update versions vary by product model. For example:

• HP Elite Dragonfly requires firmware version 01.12.00 or later
• HP EliteBook 1040 G4 requires firmware version 1.41 or later
• HP ProDesk 600 G5 Desktop Mini PC requires firmware version 02.11.00 or later

Consult the HP advisory for the specific minimum fixed version for your product.

Workarounds

• Enable Secure Boot to prevent execution of unauthorized firmware components where possible
• Configure BIOS/UEFI administrator passwords to restrict unauthorized firmware modifications
• Enable HP Sure Start technology if available on your devices to provide firmware attack detection and recovery
• Implement physical security controls to limit local access to affected systems until patches can be deployed

# Verify current BIOS version on Windows (run as Administrator)
wmic bios get smbiosbiosversion

# HP provides BIOS update utilities - example command-line update
# Download appropriate firmware from HP Support
# Run the BIOS update utility with silent/unattended switches
HPQFlash.exe /s /f /p:"BIOSPassword"

# Verify Secure Boot status on Windows
Confirm-SecureBootUEFI

# Check HP Sure Start status (on supported models)
Get-WmiObject -Namespace "root\HP\InstrumentedBIOS" -Class HP_BIOSSetting | Where-Object {$_.Name -like "*Sure*"}