CWE Rule 427

This issue occurs when you call an external command with a relative path or without a path.

This defect also finds results that the Execution of externally controlled command defect checker finds.

By using a relative path or no path to call an external command, your program uses an unsafe search process to find the command. An attacker can control the search process and replace the intended command with a command of their own.

When you call an external command, specify the full path.

# define _GNU_SOURCE
# include <sys/types.h>
# include <sys/socket.h>
# include <unistd.h>
# include <stdio.h>
# include <stdlib.h>
# include <wchar.h>
# include <string.h>
# define MAX_BUFFER 100

void rel_path()
{
    char * data;
    char data_buf[MAX_BUFFER] = "";
    data = data_buf;

    strcpy(data, "ls -la");
    FILE *pipe;
    pipe = popen(data, "wb");  //Noncompliant
    if (pipe != NULL) pclose(pipe);
}

In this example, Bug Finder flags popen because it tries to call ls -la using a relative path to the ls command. An attacker can manipulate the command to use a malicious version.

One possible correction is to use the full path when calling the command.

# define _GNU_SOURCE
# include <sys/types.h>
# include <sys/socket.h>
# include <unistd.h>
# include <stdio.h>
# include <stdlib.h>
# include <wchar.h>
# include <string.h>
# define MAX_BUFFER 100

void rel_path()
{
    char * data;
    char data_buf[MAX_BUFFER] = "";
    data = data_buf;

    strcpy(data, "/usr/bin/ls -la");
    FILE *pipe;
    pipe = popen(data, "wb");  
    if (pipe != NULL) pclose(pipe);
}

This issue occurs when library loading routines that load an external library use a relative path or do not use a path at all.

By using a relative path or no path to load an external library, your program uses an unsafe search process to find the library. An attacker can control the search process and replace the intended library with a library of their own.

When you load an external library, specify the full path.

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

void relative_path()
{
    dlopen("liberty.dll",RTLD_LAZY); //Noncompliant
}

In this example, dlopen opens the liberty library by calling only the name of the library. However, this call to the library uses a relative path to find the library, which is unsafe.

One possible correction is to use the full path to the library when you load it into your program.

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

void relative_path()
{
    dlopen("/home/my_libs/library/liberty.dll",RTLD_LAZY);
}