CVE-2024-11796

Executive Summary

CVE-2024-11796 is a critical out-of-bounds write vulnerability in Fuji Electric Monitouch V-SFT, specifically during the parsing of V9C files. This flaw allows remote attackers to execute arbitrary code on affected installations, but requires user interaction (e.g., opening a malicious file or visiting a malicious page). The vulnerability stems from improper validation of user-supplied data, leading to a write past the end of an allocated buffer. With a CVSS score of 7.8, it poses a significant risk to industrial control systems (ICS) environments where Monitouch V-SFT is used for HMI (Human-Machine Interface) configuration. No public exploit or patch is currently available, making proactive detection and mitigation critical.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects a proprietary industrial software component (Fuji Electric Monitouch V-SFT) used in OT/ICS environments. Supply chain risks include the distribution of malicious V9C files via email, downloads, or compromised vendor channels.

CVSS Breakdown & Threat Level

• CVSS Score: 7.8 (High)
• Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
• Attack Vector (AV): Local (requires user to open a file)
• Attack Complexity (AC): Low
• Privileges Required (PR): None
• User Interaction (UI): Required (victim must open malicious file)
• Scope (S): Unchanged
• Confidentiality (C): High
• Integrity (I): High
• Availability (A): High
• Threat Level: Critical in OT/ICS contexts due to potential for RCE in HMI configuration tools.

Deep Dive & Mechanics

The vulnerability resides in the V9C file parser of Fuji Electric Monitouch V-SFT (version V9C). The software fails to validate the size of user-supplied data when reading V9C files, leading to a classic buffer overflow (out-of-bounds write). An attacker can craft a malicious V9C file containing oversized data in a specific field, causing the parser to write beyond the allocated buffer. This overwrites adjacent memory, potentially corrupting critical data structures or function pointers. Successful exploitation allows arbitrary code execution in the context of the current process (typically the user running V-SFT). The attack requires user interaction, such as opening the file via email attachment or a web download.

Vulnerable vs. Patched Code

Since no patch is available, a comparison cannot be made. However, the vulnerable code likely lacks bounds checking on input data length. A patched version would include validation such as:

// Vulnerable pseudo-code
void parse_v9c_field(char *input, int input_len) {
    char buffer[256];
    memcpy(buffer, input, input_len); // No bounds check
}

// Patched pseudo-code
void parse_v9c_field(char *input, int input_len) {
    char buffer[256];
    if (input_len > sizeof(buffer)) {
        // Handle error
        return;
    }
    memcpy(buffer, input, input_len);
}

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• Fuji Electric Monitouch V-SFT V9C installed on a Windows VM.
• A tool to craft malicious V9C files (e.g., Python with struct module).

Steps:

1. Create a malicious V9C file with an oversized field (e.g., a long string in a tag name).
2. Host the file on a web server or send via email.
3. Victim opens the file in V-SFT, triggering the overflow.
4. Execute shellcode to spawn a reverse shell.

Example Python script to generate a malicious V9C file:

import struct

# Craft a malicious V9C file with overflow
payload = b"A" * 300  # Overflow buffer
# V9C file header (simplified)
header = b"V9C\x00"
# Write to file
with open("malicious.v9c", "wb") as f:
    f.write(header)
    f.write(payload)

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

Blue Team (Defense & Detection)

Detection:

• Monitor for unusual V9C file access or crashes in V-SFT.
• Use endpoint detection rules (see Sigma/YARA below).
• Restrict execution of V-SFT to trusted users and sandboxed environments.

Mitigation:

• Disable automatic file opening in V-SFT.
• Use application whitelisting to prevent untrusted V9C files.
• Implement network segmentation to limit exposure.

Indicators of Compromise (IOCs)

• File Hashes: (None available; generate upon discovery)
• Network Indicators: Connections to unknown IPs after V-SFT crash.
• Process Anomalies: V-SFT process (e.g., VFT.exe) crashing or spawning child processes (e.g., cmd.exe, powershell.exe).
• File Artifacts: Malicious V9C files with unusually large sizes or unexpected structures.
• Registry Changes: Modifications to HKEY_CURRENT_USER\Software\Fuji Electric\Monitouch V-SFT.

Detection Engineering

YARA Rule

rule CVE_2024_11796_Malicious_V9C {
    meta:
        description = "Detects malicious V9C files exploiting CVE-2024-11796"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-11796"
    strings:
        $v9c_header = "V9C"
        $overflow = { 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 } // 16 A's
    condition:
        $v9c_header at 0 and #overflow > 10
}

Sigma Rule

title: CVE-2024-11796 Fuji Electric V-SFT V9C File Parsing RCE
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects process crashes or anomalous behavior from V-SFT when opening V9C files
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\VFT.exe'
        CommandLine|contains: '.v9c'
    condition: selection
falsepositives:
    - Legitimate V9C file usage
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-11796 Fuji Electric V-SFT V9C File Download"; flow:to_server,established; content:"V9C"; nocase; fileext:"v9c"; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Disable automatic file opening in V-SFT. Educate users not to open untrusted V9C files.
• Short-term: Implement application whitelisting to block V-SFT from executing untrusted files. Use endpoint detection and response (EDR) to monitor for exploitation attempts.
• Long-term: Apply patches from Fuji Electric when available. Consider migrating to alternative HMI configuration tools if no patch is released.
• Network: Segment OT networks from IT networks. Use web filtering to block downloads of V9C files from untrusted sources.

Valters IT