Insecure Default Variable Initialization

The software, by default, initializes an internal variable with an insecure or less secure value than is possible.


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

This code attempts to login a user using credentials from a POST request:

// $user and $pass automatically set from POST request
if (login_user($user,$pass)) {
  $authorized = true;

if ($authorized) {

Because the $authorized variable is never initialized, PHP will automatically set $authorized to any value included in the POST request if register_globals is enabled. An attacker can send a POST request with an unexpected third value 'authorized' set to 'true' and gain authorized status without supplying valid credentials.

Here is a fixed version:

$user = $_POST['user'];
$pass = $_POST['pass'];
$authorized = false;
if (login_user($user,$pass)) {
  $authorized = true;

This code avoids the issue by initializing the $authorized variable to false and explicitly retrieving the login credentials from the $_POST variable. Regardless, register_globals should never be enabled and is disabled by default in current versions of PHP.

See Also

SFP Secondary Cluster: Other Exposures

This category identifies Software Fault Patterns (SFPs) within the Other Exposures cluster.

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses without Software Fault Patterns

CWE identifiers in this view are weaknesses that do not have associated Software Fault Patterns (SFPs), as covered by the CWE-888 view. As such, they represent gaps in...

CWE Cross-section

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...

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