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OS command injection vulnerabilities occur when an application does not sanitize externally obtained inputs input and allows the execution of arbitrary system commands (with carefully chosen arguments) or an external program.

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A weakness in a privileged program caused by relying on untrusted sources such as the environment (See ENV35-J. Provide a trusted environment and sanitize all inputs), can result in the execution of a command or a program which that has more privileges than those possessed by a typical user. This noncompliant code snippet example shows such a vulnerability and can be best described as ; it is a variant of an OS command injection vulnerability.

When the single argument version of the Runtime.exec() method is invoked, the arguments are parsed by a StringTokenizer into separate tokens. Consequently, any command separators maliciously inserted into the argument will do not delimit the original command and an adversary will be is unable to proceed with in executing arbitrary system commands. This code is however, equally vulnerable as an attacker can easily invoke an external (privileged) program, despite the presence of a security manager.

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A less likely, though more pernicious form of OS command injection is portrayed in this noncompliant code example. The program spawns a shell (*nix) or a command prompt (Windows) and allows passing arguments to external programs. Sometimes the shell or prompt is just used to set an environment variable to a user defined value from within the program. The programName string is expected to hold the program's name, as well as the arguments.

An adversary can terminate the command with a command separator (such as '&&' and '||') or cause the output of the program to be piped to a sensitive file for the purpose of causing a denial of service (privileged program), or even worse, redirect some sensitive output to a non sensitive location.

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Process proc;
int filename = Integer.parseInt(System.getproperty("program.name")); // only allow integer choices
Runtime runtime = Runtime.getRuntime();

switch(filename) {
  case 1: proc = runtime.exec("hardcoded\program1"); break; // option 1
  case 2: proc = runtime.exec("hardcoded\program2"); break; // option 2
  default: System.out.println("Invalid option!"); break; 
}

Compliant Solution

An alternative is to read the file names from a secure directory. The security policy file may grant permissions to the application to read files from a specific directory. The security manager must be used when running the application. (ENV30-J. Create a secure sandbox using a Security Manager)

Risk Assessment

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