299
Example Language: C (Bad)
void host_lookup(char *user_supplied_addr){
struct hostent *hp;
in_addr_t *addr;
char hostname[64];
in_addr_t inet_addr(const char *cp);
/*routine that ensures user_supplied_addr is in the right format for conversion */
validate_addr_form(user_supplied_addr);
addr = inet_addr(user_supplied_addr);
hp = gethostbyaddr( addr, sizeof(struct in_addr), AF_INET);
strcpy(hostname, hp->h_name);
}
This function allocates a buffer of 64 bytes to store the hostname, however there is no guarantee
that the hostname will not be larger than 64 bytes. If an attacker specifies an address which
resolves to a very large hostname, then the function may overwrite sensitive data or even
relinquish control flow to the attacker.
Note that this example also contains an unchecked return value (CWE-252) that can lead to a
NULL pointer dereference (CWE-476).
Example 2:
This example applies an encoding procedure to an input string and stores it into a buffer.
Example Language: C (Bad)
char * copy_input(char *user_supplied_string){
int i, dst_index;
char *dst_buf = (char*)malloc(4*sizeof(char) * MAX_SIZE);
if ( MAX_SIZE <= strlen(user_supplied_string) ){
die("user string too long, die evil hacker!");
}
dst_index = 0;
for ( i = 0; i < strlen(user_supplied_string); i++ ){
if( '&' == user_supplied_string[i] ){
dst_buf[dst_index++] = '&';
dst_buf[dst_index++] = 'a';
dst_buf[dst_index++] = 'm';
dst_buf[dst_index++] = 'p';
dst_buf[dst_index++] = ';';
}
else if ('<' == user_supplied_string[i] ){
/* encode to &lt; */
}
else dst_buf[dst_index++] = user_supplied_string[i];
}
return dst_buf;
}
The programmer attempts to encode the ampersand character in the user-controlled string,
however the length of the string is validated before the encoding procedure is applied. Furthermore,
the programmer assumes encoding expansion will only expand a given character by a factor of
4, while the encoding of the ampersand expands by 5. As a result, when the encoding procedure
expands the string it is possible to overflow the destination buffer if the attacker provides a string of
many ampersands.
Example 3:
The following example asks a user for an offset into an array to select an item.
Example Language: C (Bad)
int main (int argc, char **argv) {
char *items[] = {"boat", "car", "truck", "train"};
CWE Version 4.14
CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer
CWE-119: Improper Restriction of Operations
within the Bounds of a Memory Buffer 300
int index = GetUntrustedOffset();
printf("You selected %s\n", items[index-1]);
}
The programmer allows the user to specify which element in the list to select, however an attacker
can provide an out-of-bounds offset, resulting in a buffer over-read (CWE-126).
Example 4:
In the following code, the method retrieves a value from an array at a specific array index location
that is given as an input parameter to the method
Example Language: C (Bad)
int getValueFromArray(int *array, int len, int index) {
int value;
// check that the array index is less than the maximum
// length of the array
if (index < len) {
// get the value at the specified index of the array
value = array[index];
}
// if array index is invalid then output error message
// and return value indicating error
else {
printf("Value is: %d\n", array[index]);
value = -1;
}
return value;
}
However, this method only verifies that the given array index is less than the maximum length of
the array but does not check for the minimum value (CWE-839). This will allow a negative value
to be accepted as the input array index, which will result in a out of bounds read (CWE-125) and
may allow access to sensitive memory. The input array index should be checked to verify that is
within the maximum and minimum range required for the array (CWE-129). In this example the if
statement should be modified to include a minimum range check, as shown below.
Example Language: C (Good)
...
// check that the array index is within the correct
// range of values for the array
if (index >= 0 && index < len) {
...
Example 5:
Windows provides the _mbs family of functions to perform various operations on multibyte strings.
When these functions are passed a malformed multibyte string, such as a string containing a
valid leading byte followed by a single null byte, they can read or write past the end of the string
buffer causing a buffer overflow. The following functions all pose a risk of buffer overflow: _mbsinc
_mbsdec _mbsncat _mbsncpy _mbsnextc _mbsnset _mbsrev _mbsset _mbsstr _mbstok _mbccpy
_mbslen
Observed Examples
Reference Description
CVE-2021-22991 Incorrect URI normalization in application traffic product leads to buffer
overflow, as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2021-22991
CVE-2020-29557 Buffer overflow in Wi-Fi router web interface, as exploited in the wild per CISA
KEV.
CWE Version 4.14
CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer
CWE-119: Improper Restriction of Operations
within the Bounds of a Memory Buffer