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); /* mode is 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.
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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.
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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
- ISO/IEC 9899-1999 Section 7.19.5.3, The fopen function
- Open Group 04 The open function
- ISO/IEC TR 24731-2006 Section 6.5.2.1, The fopen_s function
- CVE-2006-1174