CVE-2024-42444

Executive Summary

CVE-2024-42444 is a Time-of-Check Time-of-Use (TOCTOU) race condition vulnerability in AMI AptioV BIOS firmware. An attacker with local access can exploit this flaw to execute arbitrary code on the target device. The vulnerability has a CVSS score of 7.5 (High) and currently has no known public exploit or patch. The EPSS score is 0.0%, indicating low exploitation likelihood in the wild, but the impact is severe due to the potential for full system compromise.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in AMI AptioV BIOS, affecting hardware supply chain security. Organizations should verify the integrity of BIOS updates and monitor for vendor advisories.

CVSS Breakdown & Threat Level

• CVSS Score: 7.5 (High)
• Vector: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
• Attack Vector: Local (AV:L)
• Attack Complexity: High (AC:H) – requires precise timing and race condition exploitation
• Privileges Required: High (PR:H) – attacker needs local access with elevated privileges
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H)
• Integrity Impact: High (I:H)
• Availability Impact: High (A:H)

Threat Level: High. Although exploitation is complex, successful compromise leads to arbitrary code execution at the firmware level, bypassing OS security controls.

Deep Dive & Mechanics

The vulnerability resides in the AMI AptioV BIOS firmware, specifically in a component that performs a check-then-use operation on a shared resource (e.g., a memory region or configuration register). A TOCTOU race condition occurs when the state of the resource changes between the time it is checked (e.g., for permissions or integrity) and the time it is used. An attacker can exploit this by rapidly modifying the resource after the check but before the use, leading to execution of arbitrary code.

Attack Scenario:

1. Attacker gains local access to the target system (e.g., via a compromised user account or physical access).
2. Attacker identifies a race window in the BIOS code where a resource is validated and then used.
3. Attacker uses a timing attack (e.g., spinning threads or using precise delays) to modify the resource after validation but before use.
4. The BIOS executes the attacker-controlled code, leading to full system compromise.

Root Cause: Lack of proper locking or atomic operations in the BIOS code handling the resource.

Vulnerable vs. Patched Code

Since no patch is available, a hypothetical vulnerable code snippet and its patched version are provided.

Vulnerable Code (C-like pseudocode):

if (validate_resource(resource)) {
    // Race window: resource can be modified here
    use_resource(resource);
}

Patched Code:

lock_resource(resource);
if (validate_resource(resource)) {
    use_resource(resource);
}
unlock_resource(resource);

The patched version uses a lock to ensure atomicity, preventing the race condition.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Local access to a system with AMI AptioV BIOS (version unknown).
• Elevated privileges (e.g., root or Administrator).
• Knowledge of the vulnerable BIOS component.

Exploitation Steps:

1. Identify the race window by reverse engineering the BIOS binary (e.g., using UEFITool or IDA Pro).
2. Write a proof-of-concept exploit that spawns multiple threads to modify the target resource.
3. Use timing primitives (e.g., rdtsc or sleep) to synchronize the race.
4. Execute the exploit to trigger arbitrary code execution.

Example Exploit Skeleton (Python with ctypes):

import ctypes
import threading
import time

# Hypothetical memory address of the resource
resource_addr = 0x12345678

def race_thread():
    while True:
        ctypes.memmove(resource_addr, b"\x90\x90\x90\x90", 4)  # NOP sled

def trigger():
    # Trigger the vulnerable code path
    # This is a placeholder; actual implementation depends on BIOS specifics
    pass

# Start race thread
t = threading.Thread(target=race_thread)
t.daemon = True
t.start()

# Trigger the vulnerability
trigger()

Blue Team

Detection:

• Monitor for unusual BIOS configuration changes or unexpected system behavior.
• Use hardware security modules (HSMs) to verify BIOS integrity.
• Implement runtime integrity monitoring (e.g., using Intel TXT or AMD SVM).

Mitigation:

• Apply vendor patches when available.
• Restrict physical and local access to systems.
• Enable Secure Boot and BIOS password protection.

Indicators of Compromise (IOCs)

• File Hashes: None available (no known exploit code).
• Network Signatures: None (local attack).
• Behavioral IOCs:
  • Unexpected BIOS updates or configuration changes.
  • System crashes or hangs during boot.
  • Unusual memory access patterns at the firmware level.

Detection Engineering

YARA Rule

rule CVE_2024_42444_BIOS_TOCTOU {
    meta:
        description = "Detects potential TOCTOU exploitation in AMI AptioV BIOS"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-42444"
    strings:
        $race_pattern = { 48 8B 05 ?? ?? ?? ?? 48 85 C0 74 ?? 48 8B 40 08 }  // Example pattern
    condition:
        $race_pattern
}

Sigma Rule

title: Potential TOCTOU Exploitation in AMI AptioV BIOS
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit CVE-2024-42444 via local race condition
author: Valters IT
logsource:
    product: windows
    service: sysmon
detection:
    selection:
        EventID: 1
        Image: '*\\exploit.exe'
    condition: selection
falsepositives:
    - Legitimate BIOS update tools
level: high

Suricata Rule

alert ip any any -> any any (msg:"CVE-2024-42444 TOCTOU Exploit Attempt"; flow:to_server; content:"|90 90 90 90|"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

• Monitor AMI’s security advisories for a patch.
• Restrict local access to systems (physical and logical).
• Enable BIOS password and Secure Boot.

Long-term Mitigation:

• Implement hardware-based root of trust (e.g., TPM).
• Use runtime firmware integrity verification.
• Apply principle of least privilege to local users.

Workarounds:

• Disable unnecessary BIOS features that may expose the vulnerable component.
• Use virtualization-based security (VBS) to isolate critical processes.

Valters IT
DevSecOps & Cyber Threat Intelligence