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A good example is the null-terminated byte string type in C. If a string lacks the terminating null character, the program may be tricked into accessing storage after the string as legitimate data. A program may, as a result, process a string it should not process, which might be a security flaw in itself. It may also cause the program to abort, which might be a denial-of-service attack.

The emphasis of this rule recommendation is to avoid producing unterminated strings; it does not address processing of already existing unterminated strings. However, by preventing the creation of unterminated strings, the need to process them is greatly lessened.

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char *source;
char a[NTBS_SIZE];
/* ... */
if (source) {
  char* b = strncpy(a, source, 5); // b == a
}
else {
  /* Handle null string condition */
}

Compliant Solution (strncpy_s(), C11 Annex K)

The C11 Annex K strncpy_s() function copies up to n characters from the source array to a destination array [TR 24731]. If no null character was copied from the source array, the nth position in the destination array is set to a null character, guaranteeing that the resulting string is null-terminated.

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Failure to enforce type safety can result in type errors in the program.

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)

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Image Added Image Added API09-C. Compatible values should have the same typeImage Removed Image Removed Image Removed