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Insecure Use of Dangerous Function

This vulnerability category covers the following issues:

Fixing Command Injection​

About Command Injection

What is command injection?​

Command injection is a type of security vulnerability that allows an attacker to execute arbitrary commands on a target system. It occurs when an application accepts user input as part of a command or query that is executed by the system without proper validation or sanitization.

For example, consider a web application that allows users to search for products by entering a product name. If the application does not properly sanitize user input and passes the input directly to the operating system's command shell, an attacker can insert malicious code into the input that could be executed by the command shell.

This could result in the attacker gaining unauthorized access to the system or performing other malicious actions.

Check out this video for a high-level explanation:

What is the impact of command injection?​

A successful command injection attack can have a wide-ranging impact, depending on the system and the attacker's goals. Here are a few potential impacts:

  • Unauthorized access: An attacker may be able to gain unauthorized access to a system or application, giving them access to sensitive data or functionality.
  • Data theft: An attacker may be able to steal data from the system, including personally identifiable information, financial data, or other sensitive data.
  • Malware installation: An attacker may be able to install malware on the system, allowing them to further compromise the system or use it as a launching point for other attacks.
  • Denial of service: An attacker may be able to launch a denial-of-service attack by executing commands that overwhelm the system's resources, or deleting important system files.
  • System compromise: In some cases, a successful command injection attack can lead to complete compromise of the system, allowing the attacker to take full control.

How to prevent command injection?​

Some measures that can help prevent command injection attacks are:

  • Input validation and sanitization: Ensure that user input is validated and sanitized before it is used in any system command. Use regular expressions or input filters to remove or encode any special characters that could be used to execute arbitrary commands.
  • Use parameterized queries: When executing commands that include user input, use parameterized queries instead of string concatenation.
  • Limit permissions: Limit the permissions of the user account that runs the application to only those that are necessary to perform its functions.
  • Perform regular security audits: Regularly audit your system and application for security vulnerabilities, including command injection vulnerabilities. Use automated tools and manual testing to identify potential issues and fix them before they can be exploited.
  • Educate your development team: Educate your development team about the risks of command injection attacks and the measures that can be taken to prevent them.

References​

Taxonomies​

Explanation & Prevention​

Training​

Option A: Use operating system APIs securely​

  1. Go through the issues that GuardRails identified in the PR/MR.

  2. Locate the dangerous function. For example:

    def index(conn, %{"test" => test}) do
      System.cmd(test, [])
    end

    or:

    def index(conn, %{"test" => test}) do
      os.cmd(test, [])
    end

  3. Take one of the following actions:

    • If the functionality is not required, then remove it
    • Ensure that no user input is processed by the function
    • If user input is processed, ensure that no special characters are allowed. E.g. validate that the user input only contains alphanumeric values.
    • Use an indirect list of allowed commands. E.g. as shown below:
    def index(conn, %{"test" => test}) do
      case test do
        "command1" -> :os.cmd('command1', [])
        "command2" -> :os.cmd('command2', [])
        _ -> {:error, "Invalid command"}
      end
    end

  4. Test it and ensure the functionality works as expected

  5. Ship it 🚢 and relax 🌴

Fixing Code Injection​

About Code Injection

What is code injection?​

Code injection is a security vulnerability that occurs when an application generates code dynamically and does not properly validate or sanitize user input before using it to generate the code.

The main difference between command injection and code injection is that command injection focuses on executing arbitrary system commands, while code injection focuses on injecting and executing arbitrary code within a program or system.

Code Injection is limited by the functionality of the injected language itself.

Check out this video for a high-level explanation:

What is the impact of code injection?​

A successful code injection attack can have a wide-ranging impact, depending on the system and the attacker's goals. Here are a few potential impacts:

  • Unauthorized access: An attacker may be able to gain unauthorized access to a system or application, giving them access to sensitive data or functionality.
  • Data theft: An attacker may be able to steal data from the system, including personally identifiable information, financial data, or other sensitive data.
  • Malware installation: An attacker may be able to install malware on the system, allowing them to further compromise the system or use it as a launching point for other attacks.
  • Denial of service: An attacker may be able to launch a denial-of-service attack by executing code that overwhelms the system's resources.
  • System compromise: In some cases, a successful code injection attack can lead to the complete compromise of the system.

How to prevent code injection?​

Some measures that can help prevent code injection attacks are:

  • Input validation and sanitization: Ensure that user input is validated and sanitized before it is used to generate code.
  • Perform regular security audits: Regularly audit your system and application for security vulnerabilities, including code injection vulnerabilities. Use automated tools and manual testing to identify potential issues and fix them before they can be exploited.
  • Educate your development team: Educate your development team about the risks of code injection attacks and the measures that can be taken to prevent them.

References​

Taxonomies​

Explanation & Prevention​

Training​

In Elixir, functions such as Code.eval_string, Code.eval_file, Code.eval_quoted, EEx.eval_string, and EEx.eval_file are used to evaluate code dynamically. Dynamic evaluation carries significant security risks, particularly if user input is ever passed into these functions without adequate sanitization.

A brief explanation of each function is shown below:

  1. Code.eval_string and Code.eval_file: These functions evaluate a string or file as Elixir code.
  2. Code.eval_quoted: This function evaluates Elixir quoted expressions.
  3. EEx.eval_string and EEx.eval_file: These functions evaluate a string or file as Elixir Embedded (EEx) templates. EEx templates allow Elixir code to be embedded within them.

As a general rule for safe practice, it's best to refrain from using these functions. However, if their usage is necessary, ensure that they never evaluate untrusted user input as code or as part of a template.

A step-by-step instruction for avoiding code injection is shown for Code.eval_string below.

Option A: Use dangerous APIs securely​

  1. Go through the issues that GuardRails identified in the PR/MR.

  2. Locate the following code pattern:

    def index(conn, %{"test" => test}) do
      Code.eval_string(test)
    end

  3. Depending on the specifics of your application, choose the most appropriate course of action:

  • Removal: If the functionality provided by the function is not necessary or can be achieved through safer means, consider removing it altogether.
  • User Input Sanitization: If the function processes user input, ensure that the input is properly sanitized before being processed.
  • Limit Function Access: If possible, restrict the scope of the functions accessible through user input. Limit these to only the ones absolutely necessary for your application to function as expected.
  1. Test it and ensure the functionality works as expected
  2. Ship it 🚢 and relax 🌴
Last updated on by Stefan Streichsbier