Use of Hard-coded, Security-relevant Constants

Description

If the developer does not find all occurrences of the hard-coded constants, an incorrect policy decision may be made if one of the constants is not changed. Making changes to these values will require code changes that may be difficult or impossible once the system is released to the field. In addition, these hard-coded values may become available to attackers if the code is ever disclosed.

Demonstrations

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

The usage of symbolic names instead of hard-coded constants is preferred.

The following is an example of using a hard-coded constant instead of a symbolic name.

char buffer[1024];
...
fgets(buffer, 1024, stdin);

If the buffer value needs to be changed, then it has to be altered in more than one place. If the developer forgets or does not find all occurrences, in this example it could lead to a buffer overflow.

enum { MAX_BUFFER_SIZE = 1024 };
...
char buffer[MAX_BUFFER_SIZE];
...
fgets(buffer, MAX_BUFFER_SIZE, stdin);

In this example the developer will only need to change one value and all references to the buffer size are updated, as a symbolic name is used instead of a hard-coded constant.

See Also