CVE-2023-28149

Executive Summary

CVE-2023-28149 is a vulnerability in the IhisiServiceSmm module within InsydeH2O firmware, affecting multiple kernel versions. The flaw allows an attacker with local, high-privileged access to modify UEFI variables, potentially leading to persistent system compromise by altering boot configuration or firmware settings. This vulnerability resides in the System Management Mode (SMM) component, which operates at the highest privilege level (Ring -2), making detection and remediation challenging. The CVSS score is 0.0 due to incomplete data, but the impact is severe for systems using affected firmware.

Supply Chain & Package Security

This vulnerability is not related to software packages (NPM, PyPI, Go, Ruby) but is a firmware-level issue in the InsydeH2O UEFI BIOS. It affects the supply chain of hardware vendors using Insyde firmware, including many laptop and embedded system manufacturers. Organizations should verify their device firmware versions and apply patches from OEMs.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Uncalculated due to missing vector)
• Attack Vector: Local (requires physical or administrative access)
• Attack Complexity: Low
• Privileges Required: High (administrator/root)
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: High (potential to read firmware secrets)
• Integrity Impact: High (UEFI variable modification)
• Availability Impact: High (can brick system or bypass secure boot)
• Threat Level: High (persistent firmware-level compromise)

Deep Dive & Mechanics

The IhisiServiceSmm module is a System Management Mode (SMM) driver that provides services for UEFI variable management. The vulnerability stems from insufficient validation of input parameters when handling SMI (System Management Interrupt) requests. An attacker with local administrative privileges can craft a malicious SMI call to modify UEFI variables without proper authorization.

Root Cause: The SMM handler does not enforce access control checks for write operations on UEFI variables, allowing arbitrary modification.

Attack Flow:

1. Attacker gains local admin access (e.g., via OS compromise or physical access).
2. Attacker triggers an SMI via a custom driver or tool that communicates with the SMM.
3. The SMM handler processes the request and modifies UEFI variables (e.g., Secure Boot keys, boot order).
4. Changes persist across reboots, enabling bootkits or disabling security features.

Impact: An attacker can disable Secure Boot, install persistent malware, or brick the device.

Vulnerable vs. Patched Code

The vulnerability is in the SMM handler's lack of validation. Below is a conceptual comparison.

Vulnerable Code (Conceptual):

EFI_STATUS SmmHandler(EFI_HANDLE DispatchHandle, const void *Context, void *CommBuffer, UINTN *CommBufferSize) {
    // No access check
    UEFI_VARIABLE *var = (UEFI_VARIABLE *)CommBuffer;
    gRT->SetVariable(var->Name, &var->Guid, var->Attributes, var->DataSize, var->Data);
    return EFI_SUCCESS;
}

Patched Code (Conceptual):

EFI_STATUS SmmHandler(EFI_HANDLE DispatchHandle, const void *Context, void *CommBuffer, UINTN *CommBufferSize) {
    // Access control check
    if (!IsAuthorized(CommBuffer)) {
        return EFI_ACCESS_DENIED;
    }
    UEFI_VARIABLE *var = (UEFI_VARIABLE *)CommBuffer;
    gRT->SetVariable(var->Name, &var->Guid, var->Attributes, var->DataSize, var->Data);
    return EFI_SUCCESS;
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Local admin access on a system with vulnerable InsydeH2O firmware.
• A tool to communicate with SMM (e.g., chipsec or custom SMI trigger).

Exploitation Steps:

1. Identify vulnerable firmware version using dmidecode or fwupdmgr.
2. Use chipsec to enumerate SMI handlers and locate IhisiServiceSmm.
3. Craft a payload to modify a UEFI variable (e.g., disable Secure Boot):

   # Example using chipsec
   from chipsec.hal.smi import SMI
   smi = SMI()
   # Trigger SMI with crafted communication buffer
   smi.send_smi(0xEF, buffer=payload)
   

4. Verify changes with efibootmgr or mokutil.

Note: No public exploit code is available; this is a conceptual approach.

Blue Team

Detection:

• Monitor for unexpected SMI calls using kernel tracing (e.g., ftrace on Linux).
• Check UEFI variable integrity with efivar and compare against known good values.
• Use firmware integrity monitoring tools (e.g., fwupd with TPM measurements).

Hunting:

• Look for processes loading custom kernel modules that interact with SMM.
• Analyze system logs for unusual SMI activity (e.g., dmesg).

Indicators of Compromise (IOCs)

• File: Modified UEFI variables (e.g., SecureBoot set to 0, BootOrder changed).
• Registry/Config: Unusual entries in NVRAM.
• Network: None (local attack).
• Behavior: System boots with Secure Boot disabled or custom boot entries.
• Logs: SMI handler calls from non-standard sources.

Detection Engineering

YARA Rule

rule CVE_2023_28149_IhisiServiceSmm {
    meta:
        description = "Detects potential exploitation of CVE-2023-28149 via SMM communication"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-28149"
    strings:
        $smm_handler = "IhisiServiceSmm" nocase
        $smi_trigger = { EF 00 00 00 } // Example SMI trigger pattern
    condition:
        $smm_handler or $smi_trigger
}

Sigma Rule

title: CVE-2023-28149 - UEFI Variable Modification via SMM
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects attempts to modify UEFI variables via SMM, indicating exploitation of CVE-2023-28149
author: Valters IT
logsource:
    product: linux
    service: syslog
detection:
    selection:
        - EventID: 1
          Image: "*chipsec*"
        - EventID: 1
          Image: "*smi*"
    condition: selection
falsepositives:
    - Legitimate firmware updates
level: high

Suricata Rule

alert ip any any -> any any (msg:"CVE-2023-28149 - SMM Communication Detected"; content:"|EF 00 00 00|"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate:

• Update firmware to patched versions: kernel 5.2 >= 05.28.42, 5.3 >= 05.37.42, 5.4 >= 05.45.39, 5.5 >= 05.53.39, or 5.6 >= 05.60.39.
• Restrict local admin access to trusted users only.

Long-term:

• Enable Secure Boot and TPM-based attestation to detect firmware tampering.
• Implement runtime firmware integrity monitoring.
• Use hardware-backed security (e.g., Intel Boot Guard).

Workarounds:

• Disable SMM write protection if possible (may impact functionality).
• Monitor UEFI variable changes with efivar scripts.

Valters IT
DevSecOps & Cyber Threat Intelligence