CVE-2024-38658

Executive Summary

CVE-2024-38658 is an Out-of-Bounds Read vulnerability affecting Fuji Electric V-Server and V-Server Lite versions up to and including v4.0.19.0. This flaw allows an attacker to craft a malicious file that, when opened by a user, can lead to information disclosure and potentially arbitrary code execution. The vulnerability resides in the parsing logic of the application, where insufficient bounds checking on user-supplied data can cause the application to read beyond allocated memory buffers. This can expose sensitive data or corrupt memory, enabling code execution under the context of the logged-in user. No public proof-of-concept (PoC) or exploit code has been released, and the vendor has not yet provided a patch. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk remains significant for organizations using these products in industrial control system (ICS) environments.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects a proprietary Windows-based application from Fuji Electric used in SCADA/HMI environments. Supply chain risk is limited to the direct distribution of the vulnerable software by Fuji Electric.

CVSS Breakdown & Threat Level

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

• Attack Vector (AV): Local (L) – requires user to open a file.
• Attack Complexity (AC): Low (L) – no special conditions.
• Privileges Required (PR): None (N) – no authentication needed.
• User Interaction (UI): Required (R) – victim must open the file.
• Scope (S): Unchanged (U) – vulnerability does not cross trust boundaries.
• Confidentiality (C): High (H) – information disclosure possible.
• Integrity (I): High (H) – arbitrary code execution possible.
• Availability (A): High (H) – crash or code execution can disrupt service.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H Estimated Base Score: 7.8 (High)

Threat Level: High. While no active exploitation is reported, the potential for remote code execution in an ICS context makes this a critical concern for asset owners.

Deep Dive & Mechanics

The vulnerability is an Out-of-Bounds Read (CWE-125) in the file parsing component of V-Server and V-Server Lite. These applications are used for monitoring and controlling industrial processes. They support various file formats for project data, configuration, and visualization.

Root Cause: The application fails to validate the size of data read from a file before copying it into a fixed-size buffer. When a specially crafted file is opened, the application reads beyond the intended buffer boundary, accessing adjacent memory regions.

Attack Vector: An attacker must convince a user to open a malicious file, typically via social engineering (e.g., email attachment, malicious download). The file is likely a project file (e.g., .vpr, .vsc, or similar) that the application parses.

Impact:

1. Information Disclosure: The out-of-bounds read can leak sensitive data from memory, such as credentials, encryption keys, or other process data.
2. Arbitrary Code Execution: By carefully crafting the file, an attacker can overwrite critical data structures (e.g., function pointers, return addresses) to redirect execution flow to attacker-controlled shellcode. This allows full compromise of the affected system.

Prerequisites:

• Victim must have V-Server or V-Server Lite installed (v4.0.19.0 or earlier).
• Victim must open the malicious file.
• No special privileges required.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, based on the vulnerability type, the fix would involve adding bounds checking before memory copy operations.

Vulnerable Code Pattern (C/C++ example):

void parse_file_data(char *file_buffer, int file_size) {
    char local_buffer[256];
    // No bounds check - vulnerable to out-of-bounds read
    memcpy(local_buffer, file_buffer, file_size);
}

Patched Code Pattern:

void parse_file_data(char *file_buffer, int file_size) {
    char local_buffer[256];
    // Bounds check added
    if (file_size > sizeof(local_buffer)) {
        // Handle error, reject file
        return;
    }
    memcpy(local_buffer, file_buffer, file_size);
}

The patched version would validate that the input size does not exceed the destination buffer size before performing the copy.

Exploitation & Lab Setup

Red Team (Offensive)

Objective: Craft a malicious file to trigger out-of-bounds read and achieve code execution.

Lab Environment:

• Windows 10/11 VM with V-Server v4.0.19.0 installed.
• Python 3.x for file crafting.
• Debugger (x64dbg) for analysis.

Steps:

1. Identify File Format: Reverse engineer the file format (e.g., .vpr) using a hex editor and debugger to understand header structures and data offsets.
2. Craft Malicious File: Create a file with a manipulated size field that exceeds the expected buffer length.

   # Example Python script to craft a malicious file
   import struct
   
   # Assume file header contains a 4-byte size field at offset 0x10
   header = b'\x00' * 0x10
   size_field = struct.pack('<I', 0xFFFFFFFF)  # Large size to trigger overflow
   payload = b'A' * 0x1000  # Arbitrary data
   
   malicious_file = header + size_field + payload
   with open('malicious.vpr', 'wb') as f:
       f.write(malicious_file)
   

3. Deliver File: Send the file to the victim via email or download.
4. Trigger Exploit: Victim opens the file in V-Server. The application reads beyond the buffer, potentially leaking memory or executing shellcode if the payload is crafted to overwrite a function pointer.

Note: No public exploit exists; this is a theoretical approach.

Blue Team (Defensive)

Objective: Detect and prevent exploitation.

Detection:

• Monitor for unusual file opens by V-Server processes.
• Use endpoint detection and response (EDR) to flag memory access violations.
• Deploy application whitelisting to block unknown executables.

Prevention:

• Restrict user privileges to prevent installation of untrusted software.
• Use email filtering to block suspicious attachments.
• Implement file integrity monitoring (FIM) for critical system files.

Hunting:

• Search for crash dumps or application errors related to V-Server.
• Analyze network traffic for unusual outbound connections from V-Server hosts.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (No known malicious files yet)
• Process Names: V-Server.exe, V-ServerLite.exe
• Registry Keys: HKLM\SOFTWARE\Fuji Electric\V-Server
• Network Indicators: Unusual outbound connections from V-Server processes to unknown IPs.
• Memory Artifacts: Large memory allocations or access violations in V-Server process memory.
• File Artifacts: Files with .vpr, .vsc, or other project extensions that are unusually large or malformed.

Detection Engineering

YARA Rule

rule CVE_2024_38658_VServer_OOB_Read {
    meta:
        description = "Detects malicious files targeting CVE-2024-38658 in Fuji Electric V-Server"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-38658"
    strings:
        $magic = { 56 2D 53 65 72 76 65 72 } // "V-Server" in hex
        $size_field = { FF FF FF FF } // Potential oversized size field
    condition:
        $magic at 0 and $size_field
}

Sigma Rule

title: CVE-2024-38658 - Fuji Electric V-Server Out-of-Bounds Read
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects potential exploitation of CVE-2024-38658 via file open events
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\V-Server.exe'
            - '\V-ServerLite.exe'
        CommandLine|contains: '.vpr'
    condition: selection
falsepositives:
    - Legitimate use of V-Server project files
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-38658 - Fuji Electric V-Server Out-of-Bounds Read"; flow:to_server,established; content:"V-Server"; nocase; content:"|FF FF FF FF|"; distance:0; within:4; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate Affected Systems: Disconnect V-Server hosts from untrusted networks if possible.
2. User Awareness: Train users not to open unsolicited files from unknown sources.
3. Application Control: Use AppLocker or similar to restrict execution of V-Server to authorized users only.

Long-Term Fix:

• Vendor Patch: Await an official patch from Fuji Electric. Monitor their security advisory page.
• Upgrade: If a patched version becomes available, upgrade immediately.
• Workaround: If patching is not possible, consider using a sandbox or virtualized environment to open project files.

Compensating Controls:

• Deploy endpoint protection with behavioral analysis.
• Enable Windows Defender Exploit Guard (e.g., Control Flow Guard, Data Execution Prevention).
• Implement strict file upload filters on email and web gateways.

Valters IT
Securing Your Digital Frontier