Missing Initialization of a Variable
The software does not initialize critical variables, which causes the execution environment to use unexpected values.
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.
This function attempts to extract a pair of numbers from a user-supplied string.
This code attempts to extract two integer values out of a formatted, user-supplied input. However, if an attacker were to provide an input of the form:
then only the m variable will be initialized. Subsequent use of n may result in the use of an uninitialized variable (CWE-457).
Here, an uninitialized field in a Java class is used in a seldom-called method, which would cause a NullPointerException to be thrown.
This code first authenticates a user, then allows a delete command if the user is an administrator.
The $isAdmin variable is set to true if the user is an admin, but is uninitialized otherwise. If PHP's register_globals feature is enabled, an attacker can set uninitialized variables like $isAdmin to arbitrary values, in this case gaining administrator privileges by setting $isAdmin to true.
In the following Java code the BankManager class uses the user variable of the class User to allow authorized users to perform bank manager tasks. The user variable is initialized within the method setUser that retrieves the User from the User database. The user is then authenticated as unauthorized user through the method authenticateUser.
However, if the method setUser is not called before authenticateUser then the user variable will not have been initialized and will result in a NullPointerException. The code should verify that the user variable has been initialized before it is used, as in the following code.
This example will leave test_string in an unknown 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 be random if it is stored on the heap or stack. If the variable is declared in static memory, it might be zero or NULL. Compiler optimization might contribute to the unpredictability of this address.
When the printf() is reached, test_string might be an unexpected address, so the printf might print junk strings (CWE-457).
To fix this code, there are a couple approaches to making sure that test_string has been properly set once it reaches the printf().
One solution would be to set test_string to an acceptable default before the conditional:
Another solution is to ensure that each branch of the conditional - including the default/else branch - could ensure that test_string is set:
Weaknesses in this category are related to the rules and recommendations in the Declarations and Initialization (DCL) section of the SEI CERT Perl Coding Standard.
Weaknesses in this category are related to the rules and recommendations in the Error Handling (ERR) section of the SEI CERT C Coding Standard.
Weaknesses in this category are related to the CISQ Quality Measures for Security, as documented in 2016 with the Automated Source Code Security Measure (ASCSM) Specif...
This view (slice) covers all the elements in CWE.
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...
This view (slice) lists weaknesses that can be introduced during implementation.