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CWE-457: Use of Uninitialized Variable
 DescriptionDescription Summary The code uses a variable that has not been initialized, leading to unpredictable or unintended results.
Extended Description In some languages such as C and C++, stack variables are not initialized by default. They generally contain junk data with the contents of stack memory before the function was invoked. An attacker can sometimes control or read these contents. In other languages or conditions, a variable that is not explicitly initialized can be given a default value that has security implications, depending on the logic of the program. The presence of an uninitialized variable can sometimes indicate a typographic error in the code. Time of Introduction
Applicable PlatformsLanguages C: (Sometimes) C++: (Sometimes) Perl: (Often) PHP: (Often) Language-independent Common Consequences
Likelihood of ExploitHigh Demonstrative ExamplesExample 1 This code prints a greeting using information stored in a POST request: (Bad Code) Example
Language: PHP if (isset($_POST['names'])) { $nameArray = $_POST['names'];
} echo "Hello " . $nameArray['first']; This code checks if the POST array 'names' is set before assigning it to the $nameArray variable. However, if the array is not in the POST request, $nameArray will remain uninitialized. This will cause an error when the array is accessed to print the greeting message, which could lead to further exploit. Example 2 The following switch statement is intended to set the values of the variables aN and bN before they are used: (Bad Code) Example
Language: C int aN, Bn; switch (ctl) { case -1:
aN = 0;
bN = 0;
break;
case 0:
aN = i;
bN = -i;
break;
case 1:
aN = i + NEXT_SZ;
bN = i - NEXT_SZ;
break;
default:
aN = -1;
aN = -1;
break;
} repaint(aN, bN); In the default case of the switch statement, the programmer has accidentally set the value of aN twice. As a result, bN will have an undefined value. Most uninitialized variable issues result in general software reliability problems, but if attackers can intentionally trigger the use of an uninitialized variable, they might be able to launch a denial of service attack by crashing the program. Under the right circumstances, an attacker may be able to control the value of an uninitialized variable by affecting the values on the stack prior to the invocation of the function. Observed Examples
Potential Mitigations
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Page Last Updated:
February 20, 2013
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