CVE-2025-8645

Executive Summary

CVE-2025-8645 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 during firmware updates, enabling system call injection. With a CVSS score of 6.8 (Medium), the attack vector is physical, but the impact is severe due to full system compromise. No patch is currently available, and no public exploit code or proof-of-concept has been released.

CVSS Breakdown & Threat Level

• CVSS Score: 6.8 (Medium)
• Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Attack Vector (AV): Physical – The attacker must have physical access to the device.
• Attack Complexity (AC): Low – No special conditions required.
• Privileges Required (PR): None – No authentication needed.
• User Interaction (UI): None – No user action required.
• Scope (S): Unchanged – The vulnerability affects only the device.
• Confidentiality (C): High – Full data access possible.
• Integrity (I): High – Arbitrary code execution.
• Availability (A): High – Potential denial of service or device bricking.

Threat Level: High for physical access scenarios (e.g., car audio systems, kiosks). Remote exploitation is not possible.

Deep Dive & Mechanics

The vulnerability exists in the firmware update mechanism of the Kenwood DMX958XR. The device processes firmware update files (likely via USB or SD card) and executes system commands based on user-supplied strings (e.g., file names, metadata, or update parameters). Due to insufficient input sanitization, an attacker can inject arbitrary shell commands into these strings. When the device processes the update, the injected commands are executed with root privileges, allowing full control over the device.

Root Cause: The firmware update function uses a system call (e.g., system(), exec(), or popen()) with user-controlled input without proper escaping or validation. For example, a file name like update;malicious_command.sh could trigger command injection.

Attack Scenario:

1. Attacker gains physical access to the device (e.g., via USB port).
2. Attacker prepares a malicious firmware update file with crafted strings.
3. Device processes the update, executing injected commands.
4. Attacker achieves root-level code execution.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

void process_firmware_update(char *filename) {
    char cmd[256];
    snprintf(cmd, sizeof(cmd), "firmware_tool --update %s", filename);
    system(cmd);  // Vulnerable: no input validation
}

Patched Code (Conceptual):

void process_firmware_update(char *filename) {
    // Validate filename: only allow alphanumeric, dots, underscores, hyphens
    if (!is_valid_filename(filename)) {
        log_error("Invalid filename");
        return;
    }
    char cmd[256];
    snprintf(cmd, sizeof(cmd), "firmware_tool --update %s", filename);
    system(cmd);  // Still risky; better to use execve with sanitized args
}

Note: No official patch exists. The above is a recommended fix.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Physical access to Kenwood DMX958XR device.
• USB drive or SD card.
• Basic knowledge of shell scripting.

Exploitation Steps:

1. Create a malicious firmware update file (e.g., update.bin).
2. Embed command injection in the file name or metadata (e.g., update;id > /tmp/pwned.bin).
3. Insert the USB drive into the device.
4. Initiate the firmware update process via the device menu.
5. The injected command executes with root privileges.

Example Payload (File Name):

# File name: update;echo "pwned" > /tmp/flag.bin
# When processed, the device runs: firmware_tool --update update;echo "pwned" > /tmp/flag.bin

No public exploit code available.

Blue Team (Defense & Detection)

Detection:

• Monitor for unexpected USB/SD card insertions.
• Log all firmware update attempts and file names.
• Use file integrity monitoring on firmware update directories.

Mitigation:

• Disable automatic firmware update execution.
• Require cryptographic signature verification for updates.
• Implement strict input validation (allowlist only).

Indicators of Compromise (IOCs)

• File Names: Suspicious strings containing shell metacharacters (;, |, &, $, `, \n).
• Process Execution: Unexpected system commands spawned by the firmware update process.
• Network Traffic: Outbound connections from the device to unknown IPs (if attacker establishes reverse shell).
• File System Changes: New files in /tmp or /root with unusual names.
• Log Entries: Firmware update logs showing malformed file names.

Detection Engineering

YARA Rule

rule CVE_2025_8645_Kenwood_Command_Injection {
    meta:
        description = "Detects command injection attempts targeting Kenwood DMX958XR firmware update"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-8645"
    strings:
        $cmd_inject1 = /[;|&`$(){}]/
        $firmware_ext = ".bin" nocase
        $update_keyword = "update" nocase
    condition:
        $firmware_ext and $update_keyword and #cmd_inject1 > 0
}

Sigma Rule

title: Kenwood DMX958XR Firmware Update Command Injection Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects suspicious file names during firmware update on Kenwood DMX958XR
author: Valters IT
date: 2025-04-10
logsource:
    product: linux
    category: process_creation
detection:
    selection:
        Image|endswith: '/firmware_tool'
        CommandLine|contains:
            - ';'
            - '|'
            - '&'
            - '`'
            - '$('
    condition: selection
falsepositives:
    - Legitimate firmware updates with unusual characters (rare)
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-8645 Kenwood DMX958XR Command Injection Attempt"; flow:to_server; content:"firmware_tool"; nocase; pcre:"/[;|&`$(){}]/"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable automatic firmware updates on affected devices.
2. Restrict physical access to the device (e.g., lock USB ports).
3. Monitor logs for suspicious firmware update attempts.

Long-Term Fix:

• Kenwood must release a firmware update that:
  • Implements strict input validation (allowlist only).
  • Uses cryptographic signature verification for update files.
  • Avoids using system() or similar functions with user input.

Workaround:

• If patching is not possible, use a hardware write-protect switch on USB ports or disable the firmware update feature entirely.

Valters IT