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Compliant Solution: fopen_s() (ISO/IEC TR 24731-1)

The {{fopen_s()}} function defined in ISO/IEC TR 24731-1 \[[ISO/IEC TR 24731-2006|AA. C References#ISO/IEC TR 24731-2006]\] can be used to create a file with restriced permissions.  Specifically, ISO/IEC TR 24731-1 says: 

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. If the file is being created and first character of the mode string is 'u', then by the time the file has been closed, it shall have the system default file access permissions.

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Non-Compliant Code Example: open() (POSIX)

Wiki MarkupUsing the POSIX function {{open()}} to create a file but failing to provide access permissions for that file may cause the file to be created with unintended access permissions. This omission has been known to lead to vulnerabilities; for instance, \[[CVE-2006-1174|http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-1174]\].

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