CVE-2023-39538: AMI Aptio V Information Disclosure Flaw

CVE-2023-39538 Overview

CVE-2023-39538 is a BIOS/UEFI vulnerability in AMI AptioV that allows a local user to upload an unrestricted BMP Logo file with a dangerous type. This firmware-level vulnerability poses significant risks to system integrity, as successful exploitation can lead to a complete loss of Confidentiality, Integrity, and Availability. The vulnerability exists in the BIOS logo customization functionality, which fails to properly validate uploaded BMP image files.

Critical Impact

Local attackers with low privileges can exploit this BIOS vulnerability to potentially compromise system firmware integrity, leading to persistent threats that survive operating system reinstallation and can affect the entire boot chain.

Affected Products

• AMI AptioV (all versions prior to security patch)
• Systems using AMI AptioV BIOS firmware
• NetApp products utilizing affected AMI AptioV firmware

Discovery Timeline

• 2023-12-06 - CVE-2023-39538 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-39538

Vulnerability Analysis

This vulnerability stems from improper input validation (CWE-20) and unrestricted upload of files with dangerous types (CWE-434) within the AMI AptioV BIOS firmware. The BIOS logo customization feature allows users to upload custom BMP logo images that are displayed during the boot process. However, the implementation fails to adequately validate the contents and structure of uploaded BMP files.

The attack requires local access to the system, but only low privileges are needed to exploit it. No user interaction is required for successful exploitation. Once exploited, an attacker can achieve high impact on confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause of CVE-2023-39538 is twofold. First, improper input validation (CWE-20) means the BIOS firmware does not sufficiently validate the structure, headers, or content of BMP files before processing them. Second, unrestricted file upload (CWE-434) indicates the system accepts BMP files without proper type checking or sanitization, allowing potentially malicious file content to be processed by the firmware.

This combination allows attackers to craft malicious BMP files that, when processed by the BIOS, can trigger unintended behavior at the firmware level. Since BIOS/UEFI firmware operates at the lowest level of system software, vulnerabilities at this layer can have severe and persistent consequences.

Attack Vector

The attack vector for CVE-2023-39538 is local, meaning an attacker must have physical or local access to the target system. The exploitation process involves:

1. The attacker gains local access to the target system with low-privilege credentials
2. The attacker crafts a malicious BMP file designed to exploit the validation weakness in the BIOS logo upload functionality
3. Using BIOS configuration tools or direct firmware access, the attacker uploads the malicious BMP file as a custom boot logo
4. When the BIOS processes the malicious BMP file, it can trigger memory corruption or code execution at the firmware level

Since no verified exploit code is publicly available, the specific technical implementation remains undisclosed. For detailed technical information, refer to the AMI Security Advisory AMI-SA-2023009.

Detection Methods for CVE-2023-39538

Indicators of Compromise

• Unexpected modifications to BIOS logo settings or custom boot logo configurations
• Changes to BIOS firmware version or checksum without authorized updates
• Unusual files present in BIOS configuration storage areas
• Anomalous system behavior during boot sequence

Detection Strategies

• Implement firmware integrity monitoring to detect unauthorized changes to BIOS settings
• Enable Secure Boot and verify its configuration has not been tampered with
• Use hardware-based trusted platform module (TPM) attestation to verify firmware integrity
• Monitor for unauthorized local access attempts to BIOS configuration utilities

Monitoring Recommendations

• Deploy endpoint detection solutions that monitor firmware-level changes
• Establish baseline BIOS configurations and alert on deviations
• Implement privileged access management for local system accounts
• Conduct regular firmware integrity audits using vendor-provided tools

How to Mitigate CVE-2023-39538

Immediate Actions Required

• Review the AMI Security Advisory AMI-SA-2023009 for specific patch information
• Contact your system vendor for updated BIOS firmware that addresses this vulnerability
• Restrict local access to systems with vulnerable BIOS firmware to authorized personnel only
• Enable BIOS password protection to prevent unauthorized configuration changes

Patch Information

AMI has released security updates addressing this vulnerability. Organizations should consult the AMI Security Advisory AMI-SA-2023009 for specific patch details. NetApp customers should also review the NetApp Security Advisory NTAP-20240105-0003 for information about affected NetApp products and available updates.

System vendors who use AMI AptioV firmware will need to release BIOS updates for their specific hardware platforms. Contact your hardware vendor for firmware updates applicable to your systems.

Workarounds

• Set a strong BIOS administrator password to prevent unauthorized access to BIOS configuration
• Disable custom logo functionality in BIOS settings if not required
• Enable Secure Boot to help protect against unauthorized firmware modifications
• Restrict physical access to systems and limit local administrative privileges

# Configuration example
# Verify current BIOS version on Linux systems
sudo dmidecode -t bios | grep -E "Vendor|Version|Release"

# Check for AMI BIOS presence
sudo dmidecode -t bios | grep -i "AMI"

# Monitor BIOS settings changes (requires root)
# Document current BIOS configuration for baseline
sudo dmidecode -t 0,1,2,3 > /var/log/bios_baseline_$(date +%Y%m%d).txt