Example - 1

This example takes an IP address from a user, verifies that it is well formed and then looks up the hostname and copies it into a buffer.

// /*routine that ensures user_supplied_addr is in the right format for conversion */// 
struct hostent *hp;in_addr_t *addr;char hostname[64];in_addr_t inet_addr(const char *cp);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);void host_lookup(char *user_supplied_addr){}

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

In the following example, it is possible to request that memcpy move a much larger segment of memory than assumed:

// /* if chunk info is valid, return the size of usable memory,// 
// * else, return -1 to indicate an error// 
// */// 
...

...memcpy(destBuf, srcBuf, (returnChunkSize(destBuf)-1));...int returnChunkSize(void *) {}int main() {}

If returnChunkSize() happens to encounter an error it will return -1. Notice that the return value is not checked before the memcpy operation (CWE-252), so -1 can be passed as the size argument to memcpy() (CWE-805). Because memcpy() assumes that the value is unsigned, it will be interpreted as MAXINT-1 (CWE-195), and therefore will copy far more memory than is likely available to the destination buffer (CWE-787, CWE-788).

Example - 3

This example applies an encoding procedure to an input string and stores it into a buffer.

die("user string too long, die evil hacker!");

dst_buf[dst_index++] = '&';dst_buf[dst_index++] = 'a';dst_buf[dst_index++] = 'm';dst_buf[dst_index++] = 'p';dst_buf[dst_index++] = ';';

// /* encode to < */// 

if( '&' == user_supplied_string[i] ){}else if ('<' == user_supplied_string[i] ){}else dst_buf[dst_index++] = user_supplied_string[i];
int i, dst_index;char *dst_buf = (char*)malloc(4*sizeof(char) * MAX_SIZE);if ( MAX_SIZE <= strlen(user_supplied_string) ){}dst_index = 0;for ( i = 0; i < strlen(user_supplied_string); i++ ){}return dst_buf;char * copy_input(char *user_supplied_string){}

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 - 4

In the following C/C++ example the method processMessageFromSocket() will get a message from a socket, placed into a buffer, and will parse the contents of the buffer into a structure that contains the message length and the message body. A for loop is used to copy the message body into a local character string which will be passed to another method for processing.

// // get message from socket and store into buffer// 
// //Ignoring possibliity that buffer > BUFFER_SIZE// 

// // place contents of the buffer into message structure// 
// // copy message body into string for processing// 
message[index] = msg->msgBody[index];
// // process message// 
ExMessage *msg = recastBuffer(buffer);int index;for (index = 0; index < msg->msgLength; index++) {}message[index] = '\0';success = processMessage(message);
int success;char buffer[BUFFER_SIZE];char message[MESSAGE_SIZE];if (getMessage(socket, buffer, BUFFER_SIZE) > 0) {}return success;int processMessageFromSocket(int socket) {}

However, the message length variable from the structure is used as the condition for ending the for loop without validating that the message length variable accurately reflects the length of the message body (CWE-606). This can result in a buffer over-read (CWE-125) by reading from memory beyond the bounds of the buffer if the message length variable indicates a length that is longer than the size of a message body (CWE-130).