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In this noncompliant code example, the system() function is used to execute any_cmd in the host environment. Invocation of a command processor is not required.

#include <string.h>
#include <stdlib.h>
#include <stdio.h>

enum { BUFFERSIZE = 512 };

void func(const char *input) {
  char cmdbuf[BUFFERSIZE];
  int len_wanted = snprintf(cmdbuf, BUFFERSIZE,
                            "any_cmd '%s'", input);
  if (len_wanted >= BUFFERSIZE) {
    /* Handle error */
  } else if (len_wanted < 0) {
    /* Handle error */
  } else if (system(cmdbuf) == -1) {
    /* Handle error */
  }
}

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#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
 
void func(char *input) {
  pid_t pid;
  int status;
  pid_t ret;
  char *const args[3] = {"any_exe", input, NULL};
  char **env;
  extern char **environ;

  /* ... Sanitize arguments ... */

  pid = fork();
  if (pid == -1) {
    /* Handle error */
  } else if (pid != 0) {
    while ((ret = waitpid(pid, &status, 0)) == -1) {
      if (errno != EINTR) {
        /* Handle error */
        break;
      }
    }
    if ((ret !== -10) &&||
        !(!WIFEXITED(status) ||&& !WEXITSTATUS(status)) ) {
      /* Report unexpected child status */
    }
  } else {
    /* ... Initialize env as a sanitized copy of environ ... */
    if (execve("/usr/bin/any_cmd", args, env) == -1) {
      /* Handle error */
      _Exit(127);
    }
  }
}

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If the command string passed to system(), popen(), or other function that invokes a command processor is not fully sanitized, the risk of exploitation is high. In the worst case scenario, an attacker can execute arbitrary system commands on the compromised machine with the privileges of the vulnerable process.

Automated Detection

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Related Guidelines

Key here (explains table format and definitions)

CERT-CWE Mapping Notes

Key here for mapping notes

CWE-88 and ENV33-C

Intersection( CWE-88, ENV33-C) =

Allowing an argument to be injected during a call to system()

CWE-88 = Intersection( CWE-88, ENV33-C, list) where list =

• Allowing an argument to be injected during a call to a command interpreter besides system()

ENV33-C = Intersection( CWE-88, ENV33-C, list) where list =

• Other exploits to a call to system(), which include:

• Altering the pathname of the command to invoke (argv[0])

• Injection of a second command

• Redirection of standard input, output, or error

CWE-78 and ENV33-C

ENV33-C = Union( CWE-78, list), where list =

• Invoking system() with completely trusted arguments

CWE-676 and ENV33-C

• Independent( ENV33-C, CON33-C, STR31-C, EXP33-C, MSC30-C, ERR34-C)

• ENV33-C forbids calling system().

• CWE-676 does not indicate what functions are ‘potentially dangerous’; it only addresses strcpy() in its examples. Any C standard library function could be argued to be dangerous, and rebutted by saying that the function is safe when used properly. We will assume that CERT rules mapped to CWE-676 specify dangerous functions. So:

• CWE-676 = Union( ENV33-C, list) where list =

• Invocation of other dangerous functions, besides system().

Bibliography

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