Example - 1

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).

Example - 2

The following C/C++ example demonstrates a buffer over-read due to a missing NULL terminator. The main method of a pattern matching utility that looks for a specific pattern within a specific file uses the string strncopy() method to copy the command line user input file name and pattern to the Filename and Pattern character arrays respectively.

// /* Validate number of parameters and ensure valid content */// 
// /* copy filename parameter to variable, may cause off-by-one overflow */// 
// /* copy pattern parameter to variable, may cause off-by-one overflow */// 
char Filename[256];char Pattern[32];...strncpy(Filename, argv[1], sizeof(Filename));strncpy(Pattern, argv[2], sizeof(Pattern));printf("Searching file: %s for the pattern: %s\n", Filename, Pattern);Scan_File(Filename, Pattern);int main(int argc, char **argv){}

However, the code do not take into account that strncpy() will not add a NULL terminator when the source buffer is equal in length of longer than that provide size attribute. Therefore if a user enters a filename or pattern that are the same size as (or larger than) their respective character arrays, a NULL terminator will not be added (CWE-170) which leads to the printf() read beyond the expected end of the Filename and Pattern buffers.

To fix this problem, be sure to subtract 1 from the sizeof() call to allow room for the null byte to be added.

// /* copy filename parameter to variable, no off-by-one overflow */// 
// /* copy pattern parameter to variable, no off-by-one overflow */// 
strncpy(Filename, argv[2], sizeof(Filename)-1);Filename[255]='\0';strncpy(Pattern, argv[3], sizeof(Pattern)-1);
Pattern[31]='\0';