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External programs are commonly invoked to perform a function required by the overall system. This practice is a form of reuse and might even be considered a crude form of component-based software engineering. Command and argument injection vulnerabilities occur when an application fails to sanitize untrusted input and uses it in the execution of external programs.

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Because Runtime.exec() receives unsanitized data originating from the environment, this code is susceptible to a command injection attack.

An attacker can exploit this program using the following command:

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which first attempts to list a nonexistent dummy folder , and then prints bad to the console.

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Compliant Solution (Sanitization)

This compliant solution solution sanitizes the untrusted user input by permitting only a small group of whitelisted characters in the argument that will be passed to Runtime.exec(); all other characters are excluded.

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import java.io.File;

class DirList {
  public static void main(String[] args) throws Exception {
    File dir = new File(System.getProperty("dir"));
    if (!dir.isDirectory()) {
      System.out.println("Not a directory");
    } else {
      for (String file : dir.list()) {
        System.out.println(file);
      }
    }
  }
}

Risk Assessment

Passing untrusted, unsanitized data to the Runtime.exec() method can result in command and argument injection attacks.

Automated Detection

Related Vulnerabilities

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Android Implementation Details

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[Chess 2007]	Chapter 5, "Handling Input," section "Command Injection"
[OWASP 2005]	A Guide to Building Secure Web Applications and Web Services
[Permissions 2008]	Permissions in the Java™ SE 6 Development Kit (JDK)
[Seacord 2015]	IDS07-J. Do not pass untrusted, unsanitized data to the Runtime.exec() method LiveLesson

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