Example - 1

Here, a boolean initiailized field is consulted to ensure that initialization tasks are only completed once. However, the field is mistakenly set to true during static initialization, so the initialization code is never reached.

// // perform initialization tasks// 
...initialized = true;if (!initialized) {}private boolean initialized = true;public void someMethod() {

Example - 2

The following code intends to limit certain operations to the administrator only.

$uid = ExtractUserID($state);
// # do stuff// 
DoAdminThings();$username = GetCurrentUser();$state = GetStateData($username);if (defined($state)) {}if ($uid == 0) {}

If the application is unable to extract the state information - say, due to a database timeout - then the $uid variable will not be explicitly set by the programmer. This will cause $uid to be regarded as equivalent to "0" in the conditional, allowing the original user to perform administrator actions. Even if the attacker cannot directly influence the state data, unexpected errors could cause incorrect privileges to be assigned to a user just by accident.

Example - 3

The following code intends to concatenate a string to a variable and print the string.

char str[20];strcat(str, "hello world");printf("%s", str);

This might seem innocent enough, but str was not initialized, so it contains random memory. As a result, str[0] might not contain the null terminator, so the copy might start at an offset other than 0. The consequences can vary, depending on the underlying memory.

If a null terminator is found before str[8], then some bytes of random garbage will be printed before the "hello world" string. The memory might contain sensitive information from previous uses, such as a password (which might occur as a result of CWE-14 or CWE-244). In this example, it might not be a big deal, but consider what could happen if large amounts of memory are printed out before the null terminator is found.

If a null terminator isn't found before str[8], then a buffer overflow could occur, since strcat will first look for the null terminator, then copy 12 bytes starting with that location. Alternately, a buffer over-read might occur (CWE-126) if a null terminator isn't found before the end of the memory segment is reached, leading to a segmentation fault and crash.

Example - 4

This example will leave test_string in anunknown condition when i is the same value as err_val,because test_string is not initialized(CWE-456). Depending on where this code segment appears(e.g. within a function body), test_string might berandom if it is stored on the heap or stack. If thevariable is declared in static memory, it might be zeroor NULL. Compiler optimization might contribute to theunpredictability of this address.

test_string = "Hello World!";
char *test_string;if (i != err_val){}printf("%s", test_string);

When the printf() is reached,test_string might be an unexpected address, so theprintf might print junk strings (CWE-457).To fix this code, there are a couple approaches tomaking sure that test_string has been properly set onceit reaches the printf().One solution would be to set test_string to anacceptable default before the conditional:

test_string = "Hello World!";
char *test_string = "Done at the beginning";if (i != err_val){}printf("%s", test_string);

Another solution is to ensure that eachbranch of the conditional - including the default/elsebranch - could ensure that test_string is set:

test_string = "Hello World!";
test_string = "Done on the other side!";
char *test_string;if (i != err_val){}else {}printf("%s", test_string);