CVE-2024-52879

Executive Summary

CVE-2024-52879 is a buffer over-read vulnerability discovered in the InsydeH2O UEFI firmware kernel, specifically within the VariableRuntimeDxe driver. The flaw resides in the SmmUpdateVariablePropertySmi() SMM callback function, which uses StrCmp() to compare variable names without proper bounds checking. This can lead to a buffer over-read, potentially allowing an attacker with local access to read sensitive memory contents or cause a denial of service. The vulnerability affects multiple kernel versions (5.2 through 5.7) and requires an update to patched versions. No public exploit code or proof-of-concept is currently available, and the CVSS score is listed as 0.0, likely due to incomplete scoring data. The EPSS score is 0.0%, indicating low exploitation activity in the wild.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in InsydeH2O, which is a UEFI BIOS implementation used by various hardware vendors. The supply chain risk is moderate, as the firmware is typically pre-installed on devices and updated through OEM channels. Organizations should verify that their hardware vendors provide patched firmware versions.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder or incomplete data. Based on the vulnerability characteristics, a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Local (L) – Requires local access to the system.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): High (H) – Requires SMM privileges or kernel-level access.
• User Interaction (UI): None (N) – No user action needed.
• Scope (S): Unchanged (U) – The vulnerable component remains the same.
• Confidentiality (C): High (H) – Potential to read sensitive memory.
• Integrity (I): None (N) – No write capability.
• Availability (A): High (H) – Could cause system crash or denial of service.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:H Estimated Base Score: 6.0 (Medium)

Threat Level: Medium. The vulnerability requires high privileges (SMM) to exploit, but the impact on confidentiality and availability is significant. The lack of public exploits and low EPSS score reduces immediate risk.

Deep Dive & Mechanics

The vulnerability is located in the VariableRuntimeDxe driver, which is part of the InsydeH2O UEFI firmware. The driver handles UEFI variable operations, including variable property updates. The vulnerable function is SmmUpdateVariablePropertySmi(), which is an SMM (System Management Mode) callback. SMM is a highly privileged execution mode in x86/x64 systems, used for power management and hardware control.

The function uses StrCmp() to compare variable names. StrCmp() is a standard string comparison function that expects null-terminated strings. If the variable name provided by the caller is not properly null-terminated or is shorter than expected, StrCmp() may read beyond the allocated buffer, causing a buffer over-read. This can lead to:

• Information Disclosure: Reading sensitive data from adjacent memory, such as cryptographic keys, passwords, or other firmware secrets.
• Denial of Service: Reading invalid memory may cause a system crash or hang, especially in SMM where error handling is limited.

The root cause is insufficient validation of the variable name length before comparison. The function should use a bounded string comparison function (e.g., StrnCmp()) or verify the length of the input string.

Vulnerable vs. Patched Code

The vulnerable code uses StrCmp() directly on user-supplied variable names without length checks:

// Vulnerable code (pseudo)
EFI_STATUS SmmUpdateVariablePropertySmi(IN VARIABLE_INFO_ENTRY *VariableInfo) {
    // ...
    if (StrCmp(VariableInfo->VariableName, L"SomeVariable") == 0) {
        // Update property
    }
    // ...
}

The patched code should use a bounded comparison or validate the string length first:

// Patched code (pseudo)
EFI_STATUS SmmUpdateVariablePropertySmi(IN VARIABLE_INFO_ENTRY *VariableInfo) {
    // ...
    UINTN NameLength = StrLen(VariableInfo->VariableName);
    if (NameLength > MAX_VARIABLE_NAME_SIZE) {
        return EFI_INVALID_PARAMETER;
    }
    if (StrnCmp(VariableInfo->VariableName, L"SomeVariable", NameLength) == 0) {
        // Update property
    }
    // ...
}

The patch ensures that the variable name length is within expected bounds before comparison, preventing buffer over-read.

Exploitation & Lab Setup

Red Team

No public exploit code is available for CVE-2024-52879. To develop a proof-of-concept, an attacker would need:

• Local access to a system with vulnerable InsydeH2O firmware.
• SMM privileges or ability to trigger the SMI (System Management Interrupt) that calls SmmUpdateVariablePropertySmi().
• Knowledge of the variable name that triggers the vulnerable code path.

A potential exploitation scenario:

1. Gain local access to the target system (e.g., through a compromised user account).
2. Use a tool like chipsec or custom UEFI runtime driver to call the vulnerable SMI handler with a crafted variable name.
3. The crafted variable name should be shorter than expected or lack null termination, causing StrCmp() to read beyond the buffer.
4. Observe the system behavior (crash, memory leak) or attempt to extract data from the over-read.

Lab Setup:

• Use a virtual machine with QEMU and OVMF (UEFI firmware) or a physical system with InsydeH2O firmware.
• Install a debugger like WinDbg or GDB with UEFI support.
• Use chipsec to interact with SMM and trigger the vulnerable function.

Blue Team

To detect exploitation attempts:

• Monitor for unexpected SMI calls or SMM-related crashes in system logs.
• Use firmware integrity monitoring tools (e.g., fwupd, CHIPSEC) to verify firmware version.
• Implement endpoint detection rules for unusual UEFI variable operations.

Detection Steps:

1. Check firmware version: wmic bios get smbiosbiosversion (Windows) or dmidecode -s bios-version (Linux).
2. Compare against patched versions listed in the advisory.
3. Monitor for SMM-related events in Windows Event Log (e.g., Event ID 41, 1001).

Indicators of Compromise (IOCs)

• Firmware Version: InsydeH2O kernel 5.2 < 05.29.50, 5.3 < 05.38.50, 5.4 < 05.46.50, 5.5 < 05.54.50, 5.6 < 05.61.50, 5.7 < 05.70.50.
• System Behavior: Unexpected system crashes or hangs during UEFI variable operations.
• Memory Artifacts: Dumps showing over-read patterns in SMM memory regions.
• Log Entries: SMI handler errors or SMM-related exceptions in firmware logs.

Detection Engineering

YARA Rule

rule CVE_2024_52879_InsydeH2O_BufferOverread {
    meta:
        description = "Detects vulnerable InsydeH2O firmware versions based on string patterns"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-52879"
    strings:
        $s1 = "InsydeH2O" ascii wide nocase
        $v1 = "05.29.50" ascii wide
        $v2 = "05.38.50" ascii wide
        $v3 = "05.46.50" ascii wide
        $v4 = "05.54.50" ascii wide
        $v5 = "05.61.50" ascii wide
        $v6 = "05.70.50" ascii wide
    condition:
        $s1 and not ($v1 or $v2 or $v3 or $v4 or $v5 or $v6)
}

Sigma Rule

title: CVE-2024-52879 - InsydeH2O Buffer Over-read in VariableRuntimeDxe
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential exploitation of CVE-2024-52879 via SMM callback anomalies
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-52879
logsource:
    product: windows
    service: system
detection:
    selection:
        EventID:
            - 41  # System crash
            - 1001 # BugCheck
        Provider_Name: 'Microsoft-Windows-Kernel-Power'
    condition: selection
falsepositives:
    - Legitimate system crashes due to hardware issues
level: medium

Suricata Rule

alert ip any any -> any any (msg:"CVE-2024-52879 - InsydeH2O Buffer Over-read Attempt"; content:"|00|"; depth:1; sid:1000001; rev:1;)

Note: Suricata rule is generic as the vulnerability is local and not network-exploitable. This rule is a placeholder for network-based detection of related firmware update traffic.

Remediation & Mitigation

1. Update Firmware: Apply the patched firmware version from your hardware vendor. The fixed versions are:

   • Kernel 5.2: version 05.29.50
   • Kernel 5.3: version 05.38.50
   • Kernel 5.4: version 05.46.50
   • Kernel 5.5: version 05.54.50
   • Kernel 5.6: version 05.61.50
   • Kernel 5.7: version 05.70.50

2. Workarounds: If patching is not immediately possible:

   • Restrict local access to the system.
   • Disable unnecessary SMI handlers if supported by firmware configuration.
   • Use hardware security modules (HSM) to protect sensitive data.

3. Monitoring: Implement the detection rules above to identify potential exploitation attempts.

4. Vendor Contact: Contact your hardware vendor (e.g., Dell, HP, Lenovo) for specific firmware updates.

Valters IT