CVE-2024-52880

Executive Summary

CVE-2024-52880 is a critical security vulnerability in the InsydeH2O UEFI firmware kernel, specifically within the VariableRuntimeDxe driver. The flaw resides in the SecureBootHandler function, which improperly trusts caller-supplied DataSize and VariableNameSize parameters when validating buffer boundaries. This lack of validation can lead to a buffer overflow or out-of-bounds read, potentially allowing an attacker with local, high-privileged access (e.g., SYSTEM or kernel mode) to bypass Secure Boot protections, execute arbitrary code in the firmware context, or cause a denial of service. The vulnerability affects multiple kernel branches (5.2 through 5.7) and requires physical or administrative access to exploit, making it a high-severity firmware-level threat.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in the InsydeH2O UEFI BIOS, which is a critical component of the hardware supply chain. Organizations using devices with Insyde firmware should verify their kernel version and apply the vendor patch immediately.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0 in the NVD data, likely due to incomplete scoring. Based on the technical details, 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 beyond local access.
• Privileges Required (PR): High (H) – Requires administrative or kernel-level privileges.
• User Interaction (UI): None (N) – No user interaction needed.
• Scope (S): Changed (C) – Can affect components beyond the vulnerable driver (e.g., Secure Boot policy).
• Confidentiality (C): High (H) – Potential to read sensitive firmware data.
• Integrity (I): High (H) – Can modify Secure Boot variables.
• Availability (A): High (H) – Can cause system instability or denial of service.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H Estimated Base Score: 8.2 (High)

Threat Level: High. While exploitation requires high privileges, the impact on Secure Boot integrity and firmware security is severe.

Deep Dive & Mechanics

The vulnerability is in the SecureBootHandler function within the VariableRuntimeDxe driver of InsydeH2O. This driver manages UEFI variables, including those related to Secure Boot (e.g., SecureBoot, PK, KEK, db, dbx). The function is responsible for handling requests to read or write these variables.

The core issue is a lack of trust in caller-supplied parameters. When SecureBootHandler processes a request, it uses DataSize and VariableNameSize to determine if the provided data or variable name fits within the allocated buffer. However, these values are supplied by the caller (e.g., an OS kernel driver or UEFI application) and are not validated against the actual buffer size. An attacker with high privileges can craft a malicious request with oversized DataSize or VariableNameSize values, causing the function to read or write beyond the intended buffer boundaries.

This can lead to:

• Buffer Overflow: Writing attacker-controlled data to adjacent memory regions, potentially overwriting critical firmware structures or code.
• Out-of-Bounds Read: Leaking sensitive information from firmware memory, such as cryptographic keys or other Secure Boot variables.
• Secure Boot Bypass: By corrupting Secure Boot policy variables (e.g., db or dbx), an attacker could disable Secure Boot or enroll malicious certificates, allowing unsigned code to execute during boot.

The vulnerability is particularly dangerous because it resides in firmware, which operates below the OS. Successful exploitation could persist across reboots and evade traditional OS-level security controls.

Vulnerable vs. Patched Code

The vulnerable code is in the SecureBootHandler function. The exact source is not publicly available, but the logic can be inferred:

Vulnerable (pseudocode):

EFI_STATUS SecureBootHandler(
    IN UINT32 VariableNameSize,
    IN UINT32 DataSize,
    IN VOID *Buffer
) {
    // Trusts caller-supplied sizes without validation
    if (VariableNameSize > MAX_VARIABLE_NAME_SIZE) {
        return EFI_INVALID_PARAMETER;
    }
    // Copies data based on caller-supplied DataSize
    CopyMem(Buffer, SourceData, DataSize);
    // ...
}

Patched (pseudocode):

EFI_STATUS SecureBootHandler(
    IN UINT32 VariableNameSize,
    IN UINT32 DataSize,
    IN VOID *Buffer
) {
    // Validate caller-supplied sizes against actual buffer capacity
    if (VariableNameSize > MAX_VARIABLE_NAME_SIZE || VariableNameSize > ActualBufferSize) {
        return EFI_INVALID_PARAMETER;
    }
    if (DataSize > MAX_DATA_SIZE || DataSize > ActualBufferSize) {
        return EFI_INVALID_PARAMETER;
    }
    // Safe copy with bounds checking
    CopyMem(Buffer, SourceData, DataSize);
    // ...
}

The patch adds validation of VariableNameSize and DataSize against both predefined maximums and the actual buffer size (ActualBufferSize), preventing out-of-bounds access.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Local administrative access to a system with vulnerable InsydeH2O firmware.
• Knowledge of the target firmware version and memory layout.
• A tool to interact with UEFI runtime services (e.g., a custom UEFI driver or OS kernel module).

Exploitation Steps:

1. Identify Vulnerability: Use a UEFI scanner or manual analysis to confirm the vulnerable VariableRuntimeDxe driver.
2. Craft Malicious Request: Create a UEFI variable write request with an oversized DataSize parameter.
3. Trigger Overflow: Call the SetVariable runtime service with the crafted request, targeting a Secure Boot variable (e.g., db).
4. Overwrite Critical Data: The overflow corrupts adjacent memory, potentially overwriting the SecureBoot variable or other policy data.
5. Bypass Secure Boot: After the overflow, reboot and observe that Secure Boot is disabled or accepts a malicious certificate.

Example (Conceptual):

// Malicious UEFI application
EFI_STATUS Status;
UINTN DataSize = 0x1000; // Oversized
UINT8 *Data = AllocatePool(DataSize);
// Fill Data with attacker-controlled content
Status = gRT->SetVariable(
    L"db",
    &gEfiGlobalVariableGuid,
    EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_RUNTIME_ACCESS,
    DataSize,
    Data
);

Blue Team (Defense & Detection)

Detection:

• Monitor UEFI variable write operations for anomalous sizes (e.g., writes to db or dbx with sizes exceeding typical limits).
• Use firmware integrity monitoring tools (e.g., CHIPSEC) to detect unexpected changes to Secure Boot variables.
• Enable Secure Boot audit logging in the UEFI firmware if supported.

Mitigation:

• Apply the vendor patch immediately.
• Restrict physical access to systems.
• Use hardware security modules (HSMs) to protect firmware update keys.

Indicators of Compromise (IOCs)

• UEFI Variable Anomalies: Unusually large writes to Secure Boot variables (SecureBoot, PK, KEK, db, dbx).
• Firmware Memory Corruption: Unexpected changes in UEFI runtime services memory regions.
• Secure Boot Status Changes: Secure Boot being disabled or reporting an invalid state after a variable write.
• System Logs: Event logs showing UEFI variable write failures or buffer overflow errors (if firmware supports logging).

Detection Engineering

YARA Rule

rule CVE_2024_52880_SecureBootHandler_Overflow {
    meta:
        description = "Detects potential exploitation of CVE-2024-52880 in InsydeH2O firmware"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-52880"
    strings:
        $s1 = "SecureBootHandler" ascii wide nocase
        $s2 = "VariableRuntimeDxe" ascii wide nocase
        $s3 = "DataSize" ascii wide nocase
        $s4 = "VariableNameSize" ascii wide nocase
    condition:
        all of ($s*) and filesize < 10MB
}

Sigma Rule

title: CVE-2024-52880 - InsydeH2O SecureBootHandler Buffer Overflow
id: 8a3f7c2e-5d1b-4a9f-8c6e-2b1d3f4a5c6e
status: experimental
description: Detects attempts to exploit a buffer overflow in InsydeH2O SecureBootHandler via oversized UEFI variable writes.
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-52880
logsource:
    product: windows
    service: system
    category: uefi
detection:
    selection:
        EventID: 1  # Example: UEFI variable write event
        VariableName: "db" or "dbx" or "PK" or "KEK"
        DataSize: "> 1024"  # Unusually large size
    condition: selection
falsepositives:
    - Legitimate firmware updates
level: high

Suricata Rule

alert ip any any -> any any (msg:"CVE-2024-52880 - InsydeH2O SecureBootHandler Buffer Overflow Attempt"; content:"|53 65 63 75 72 65 42 6f 6f 74 48 61 6e 64 6c 65 72|"; nocase; content:"|56 61 72 69 61 62 6c 65 52 75 6e 74 69 6d 65 44 78 65|"; nocase; content:"|44 61 74 61 53 69 7a 65|"; distance:0; within:1024; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Patch Firmware: Update InsydeH2O to the patched versions:
   • 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. Verify Secure Boot: After patching, ensure Secure Boot is enabled and functioning correctly.
3. Restrict Access: Limit physical and administrative access to systems.

Long-Term Mitigations:

• Implement firmware integrity monitoring (e.g., using CHIPSEC or similar tools).
• Use UEFI Secure Boot with custom key enrollment to prevent unauthorized firmware changes.
• Regularly audit firmware versions and apply updates from vendors.

Workarounds (if patching is not immediately possible):

• Disable Secure Boot if not required (not recommended).
• Use hardware-based security modules to protect firmware variables.

Valters IT