CVE-2025-66173

Executive Summary

CVE-2025-66173 is a privilege escalation vulnerability affecting certain Hikvision DVR products. The flaw stems from improper authentication implementation for the serial port, allowing an attacker with physical access to connect to the device and gain unrestricted shell access. With a CVSS score of 6.2 (Medium), the vulnerability requires physical proximity, but once exploited, it can lead to full compromise of the device, including data exfiltration, persistent backdoor installation, and lateral movement within the network. No public proof-of-concept (PoC) or exploit code has been released, and no patch is currently available. The EPSS score is 0.0%, indicating low exploitation likelihood in the wild, but the risk remains significant for high-security environments.

CVSS Breakdown & Threat Level

• CVSS Score: 6.2 (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 or mitigations are required.
• Privileges Required (PR): None – No authentication needed to exploit.
• User Interaction (UI): None – No user action required.
• Scope (S): Unchanged – The exploit affects only the vulnerable component.
• Confidentiality (C): High – Full access to device data.
• Integrity (I): High – Ability to modify system files and configurations.
• Availability (A): High – Potential to disrupt device operation.

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

Deep Dive & Mechanics

The vulnerability exists in the serial port authentication mechanism of Hikvision DVR products. The serial port is typically used for debugging, firmware updates, or maintenance. Due to improper implementation, the authentication process can be bypassed, granting an attacker a root shell without valid credentials.

Root Cause: The serial port handler does not enforce proper authentication checks before spawning a shell. This could be due to:

• Hardcoded credentials that are easily guessable or publicly known.
• Missing or weak authentication logic in the firmware.
• A debug mode left enabled in production firmware.

Attack Vector: An attacker with physical access connects to the DVR’s serial port (e.g., via UART or RS-232) using a terminal adapter. By sending specific commands or simply pressing a key during boot, they gain a shell with elevated privileges.

Impact: Once shell access is obtained, the attacker can:

• Extract stored video footage and configuration files.
• Install persistent backdoors (e.g., cron jobs, modified binaries).
• Use the device as a pivot point to attack other network resources.
• Disable or tamper with recording functionality.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, based on the vulnerability description, the following pseudo-code illustrates the flaw:

Vulnerable Code (Serial Port Handler):

void serial_port_handler() {
    // No authentication check
    spawn_shell();
}

Patched Code (Expected):

void serial_port_handler() {
    if (authenticate_user()) {
        spawn_shell();
    } else {
        log_attempt();
        return;
    }
}

The patched version would require proper authentication (e.g., password prompt or cryptographic challenge) before granting shell access.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Physical access to the Hikvision DVR.
• Serial-to-USB adapter (e.g., FTDI) and terminal software (e.g., PuTTY, screen).
• Knowledge of serial port parameters (baud rate, data bits, etc.). Common settings: 115200 baud, 8N1.

Exploitation Steps:

1. Connect the serial adapter to the DVR’s serial port (often labeled on the PCB).
2. Open a terminal session with the correct settings.
3. Power on the device and observe boot messages.
4. Interrupt the boot process (e.g., press a key) to access the bootloader or debug shell.
5. Once a shell is obtained, escalate privileges if needed (often already root).

Example Command:

# Connect to serial port
screen /dev/ttyUSB0 115200
# After boot, you may see a prompt like:
# DVR> 
# Type commands to explore:
cat /etc/passwd
id

Note: No public exploit code exists; this is a generic methodology.

Blue Team

Detection:

• Monitor physical security logs for unauthorized access to DVR locations.
• Enable serial port logging if supported by the device.
• Use network monitoring to detect anomalous outbound connections from the DVR.

Prevention:

• Restrict physical access to DVRs (locked racks, CCTV monitoring).
• Disable unused serial ports in firmware settings if possible.
• Implement host-based intrusion detection (HIDS) on the DVR (if supported).

Hunting:

• Look for unexpected processes (e.g., netcat, telnet) running on the DVR.
• Check for modified system binaries (e.g., /bin/sh, /sbin/init).
• Review serial port logs for unauthorized access attempts.

Indicators of Compromise (IOCs)

• Network: Outbound connections from the DVR to unknown IPs on non-standard ports.
• File System: Presence of unauthorized files in /tmp or /root (e.g., backdoor scripts).
• Processes: Unusual processes like nc, bash -i, or telnetd.
• Logs: Serial port access logs showing repeated failed authentication attempts (if logging enabled).
• Hardware: Physical tampering evidence on the serial port pins.

Detection Engineering

YARA Rule

rule CVE_2025_66173_Hikvision_DVR_Backdoor {
    meta:
        description = "Detects potential backdoor files or modified binaries on Hikvision DVR"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-66173"
    strings:
        $backdoor_script = "nc -e /bin/sh" ascii wide nocase
        $modified_shell = { 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 } // ELF header
        $suspicious_cron = "* * * * * root /tmp/.backdoor" ascii wide nocase
    condition:
        any of them
}

Sigma Rule

title: Hikvision DVR Serial Port Exploitation Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects attempts to exploit CVE-2025-66173 via serial port access
author: Valters IT
date: 2025-04-10
logsource:
    product: linux
    service: auth
detection:
    selection:
        - EventID: 1  # Process creation
          CommandLine|contains: 
              - "screen /dev/ttyUSB"
              - "minicom"
              - "putty -serial"
        - EventID: 2  # File creation
          TargetFilename|contains: 
              - "/tmp/.backdoor"
              - "/root/.ssh/authorized_keys"
    condition: selection
falsepositives:
    - Legitimate administrative access
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-66173 Hikvision DVR Outbound Backdoor"; flow:to_server; content:"|2e 2f 62 61 63 6b 64 6f 6f 72|"; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Physical Security: Restrict access to DVR devices to authorized personnel only. Use locked enclosures and monitor with CCTV.
2. Disable Serial Port: If the serial port is not needed, disable it in the device firmware or physically disconnect the pins.
3. Network Segmentation: Place DVRs on a separate VLAN with strict firewall rules to limit lateral movement.

Long-Term Fix:

• Await an official firmware patch from Hikvision. Contact vendor support for updates.
• If patch is unavailable, consider replacing affected devices with models that have proper authentication.

Workaround:

• Implement a serial port password via bootloader configuration (if supported).
• Use a hardware serial port lock or tamper-evident seals.

Valters IT
Securing Digital Frontiers