Incorrect Calculation of Multi-Byte String Length
The product does not correctly calculate the length of strings that can contain wide or multi-byte characters.
Demonstrations
The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.
Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.
Example One
The following example would be exploitable if any of the commented incorrect malloc calls were used.
#include <stdio.h>
#include <strings.h>
#include <wchar.h>
int main() {
wchar_t wideString[] = L"The spazzy orange tiger jumped " \
"over the tawny jaguar.";
wchar_t *newString;
printf("Strlen() output: %d\nWcslen() output: %d\n",
strlen(wideString), wcslen(wideString));
/* Wrong because the number of chars in a string isn't related to its length in bytes //
newString = (wchar_t *) malloc(strlen(wideString));
*/
/* Wrong because wide characters aren't 1 byte long! //
newString = (wchar_t *) malloc(wcslen(wideString));
*/
/* Wrong because wcslen does not include the terminating null */
newString = (wchar_t *) malloc(wcslen(wideString) * sizeof(wchar_t));
/* correct! */
newString = (wchar_t *) malloc((wcslen(wideString) + 1) * sizeof(wchar_t));
/* ... */
}The output from the printf() statement would be:
Strlen() output: 0
Wcslen() output: 53See Also
Weaknesses in this category are related to incorrect calculation.
This category identifies Software Fault Patterns (SFPs) within the Incorrect Buffer Length Computation cluster (SFP10).
Weaknesses in this category are related to the creation and modification of strings.
This view (slice) covers all the elements in CWE.
This view contains a selection of weaknesses that represent the variety of weaknesses that are captured in CWE, at a level of abstraction that is likely to be useful t...
This view (slice) lists weaknesses that can be introduced during implementation.
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