Files should be created with appropriate access permissions. Creating a file with insufficient file access permissions may allow unintended access to program-critical files.

Non-compliant Code Example 1

Using the POSIX function open() to create a file but failing to provide access permissions for that file may cause that file to be created unintended access permissions. This omission has been known to lead to vulnerabilities; for instance, CVE-2006-1174.

...
int fd = open(file_name, O_CREAT | O_WRONLY); /* access permissions are missing */
if (fd == -1){
  /* Handle Error */
}
...

Compliant Code Solution 1

The third argument to open should be present to specify the access permissions for the newly created file.

...
int fd = open(file_name, O_CREAT | O_WRONLY, file_mode);
if (fd == -1){
  /* Handle Error */
}
...

Non-compliant Code Example 2

The fopen() function does not provide a mechanism to specify file access permissions. In the example below, if the call to fopen() creates a new file, the default access permissions will be implementation specific.

...
FILE * fptr = fopen(file_name, "w");
if (!fptr){
  /* Handle Error */
}
...

Compliant Code Solution 2

The fopen_s() function defined in ISO/IEC TR 24731-2006 provides some control over file access permissions. Specifically, the report states: "If the file is being created, and the first character of the mode string is not 'u', to the extent that the underlying system supports it, the file shall have a file permission that prevents other users on the system from accessing the file."

...
FILE * fptr = fopen_s(file_name, "w");
if (!fptr) {
  /* Handle Error */
}
...

References